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Contents
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Production
and Marketing of Field-Grown Trees in Georgia
 Prepared by Melvin P. Garber, Extension Horticulturist; John M. Ruter, Nursery Crops Research; and J.T. Midcap, Extension Horticulturist |
Shade trees are an important part of residential and commercial landscapes. Recent market research suggests that field-grown shade trees represent about 50 percent of the value of plant material installed in the landscape. Shade tree production in Georgia is a relatively new part of the nursery industry and has good growth potential as approximately 50 percent of the trees used in Georgia are purchased out-of-state. Currently most of the shade tree nurseries in Georgia use field production. The focus of this bulletin is the production and marketing of field-grown shade trees.
Process Flow for In-ground Deciduous Tree Production
The production of trees can be viewed as four discrete stages (see Figure 1).
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| Figure 1. In-ground Tree Production Schematic |
Tree production in Georgia has focused on the final stage (Figure 1) -- finished trees of greater than 2-inch caliper. This process includes purchasing whips or liners and planting in late fall or early spring. Normally one to four years of field production are required depending on final market size. Production of whips is not currently practiced in Georgia; most whips are purchased from Oregon or Tennessee. Further development of the shade tree industry in Georgia would benefit greatly from local production of high quality whips. As with whips, most liners (generally 1-year-old seedlings) are purchased out-of-state. There are no inherent factors that would prevent Georgia growers from producing good quality liners and whips.
Options for the initial planting stock include vegetatively or sexually propagated trees. Vegetatively propagated trees include cuttings, tissue culture, and grafted material. Sexually propagated material is synonymous with seed. Whether a grower or customer of liners, it is important to know the origin of the starter material. This will have an impact on subsequent growth and is important for you to pass on to your customer; i.e., was the seed from a northern or a southern source?
The term liner refers to the first stage of plant growth. If it is a seed-propagated plant, liner refers to the first year of growth in the seed bed. In forestry, this is referred to as a 1-0 seedling; i.e., one year in a seed bed without transplanting. Most liners of shade and ornamental trees are sold as 1-0 bareroot trees. Liners produced in the United States are generally grown in-ground, lifted during the winter, and transplanted or sold the next spring. The term liner also refers to container seedlings started either from seed, cuttings, or tissue culture plantlets and grown for one growing season. The 1-0 and container liners are used as starter material for whip production. Many catalogs refer to the liner stage as seedlings and in some cases will then have the notation of 1-0, 2-0, or 1-1. The 2-0 and 1-1 seedlings are more common for slower-growing conifer species. The 1-0 and 2-0 designations refer to seedlings grown in the planting bed for one or two years, respectively. The 1-1 designation refers to seedling grown for one year in the planting bed and then transplanted in the nursery, and grown for one year prior to harvesting.
The next stage of production is referred to as whip production. The starter material for whips is normally the 1-0 or container liner. The liner is planted in spring and is grown one season. With seedlings, plants are often cut back to the ground in the winter after the first growing season. Of the subsequent shoots that emerge, a superior shoot is selected and the remaining shoots removed. The shoot is allowed to grow for one year; i.e., the second growing season of whip production. This plant is referred to as a one-year whip, indicating one year of growth after cutback but two years of growth after transplant. If the whip is a budded plant variety, budding occurs in the fall of the first year. The plant is cut just above the bud the following spring. The shoot that emerges from the grafted bud is grown for one year. The term whip is derived from the fact that after the second year you have a tall straight stem with minimal branching.
The third stage of production is the finished tree production. The starter material can be a whip (½-inch to 1-inch caliper) or a liner. The bareroot whip is transplanted in the spring and grown for one to five years. The time will vary according to the variety and caliper of tree demanded by the market place. The material is typically harvested as a ball-and-burlap plant. An important point to remember, whether a grower or buyer, is the primary product attributes we are trying to develop at each stage of production -- liner, whip, and finished tree. The primary goal for each stage of production is:
Target Markets for In-ground Trees
Before a grower decides what to produce, it is important to know the target customer(s) for each product. In marketing terms, this requires that we have an understanding of the Market Channel Map (Figure 2). The Market Channel Map describes the products, distribution networks, and ultimate customers. With an understanding of the customer segments and their product requirements, we are better able to create a market pull. This implies that when the product is ready, a customer will be ready to purchase. The other side of the coin, production push, refers to the situation where we first decide what we want to produce and then look for a customer. Unfortunately, the production push situation usually leads to discarded plants, lower prices, and lower profit. Therefore, an important first step in product line expansion or business startup is to develop and understand the channel map for the product in question.
The channel map for in-ground shade trees shows the products and customer groups (see Figure 2). The Market Channel Map is a vital first step in development of a complete marketing plan. As a grower, you can decide which customer group and product best match your operation.
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| Figure 2. Market Channel Map for In-ground Shade Trees |
The heavy line at the center of the channel map indicates the movement of the largest volume of trees. The liners are produced in-ground as bareroot trees or as containers and sold to the whip producer. The whips are sold as bareroot plants to in-ground finishers. The in-ground finishers grow the trees for several years and sell primarily as ball and burlap (see below).
Finished trees are typically sold to landscape contractors, landscape developers, or municipalities. The finishers have typically sold directly to these customers; however, in recent years, the rewholesaler has emerged as a significant force. Rewholesalers are wholesale specialists that buy plants from the finishers and hold them in a display yard. The trees are picked up by landscape contractors, developers, and municipalities, or the rewholesaler delivers. Rewholesalers can also carry a full line of hard goods for completing landscape projects. Some finishers have set up a rewholesale yard near their growing operation. The rewholesale unit is typically open during peak spring planting.
Whips are sold to a variety of customers. Municipalities have become increasingly important customers for whips, which are purchased for street tree plantings. In the past, cities have purchased primarily large balled and burlapped (B&B) trees; however, as budgets have been reduced, they have bought smaller, less expensive trees. This should be a growing market for bareroot whips in the future.
Whips are also sold to container growers. Container growers pot the bareroot whip in early spring and normally sell these trees within 12 to 18 months. The container nurseries sell primarily to garden centers, mass merchants and landscape contractors. Although garden centers generally buy container trees, many will buy bareroot whips and produce their own container trees. The decision to buy container trees or bareroot whips is based primarily on facilities available at the garden centers and the proximity of container tree growers to the garden centers.
The liners, in addition to being sold to the whip growers, are also a good product for highway departments. They represent a small tree that is handled efficiently in large volumes, readily established, and low cost per unit. They are well suited for situations where there is plenty of time for development of the finished look and up-front money is limited.
The distribution and shipping requirements are another important element of product line evaluation. Finished trees are typically grown close to the customer because shipping cost per unit can be high. However, items such as liners and whips, which are sold as bareroot plant material, can be shipped inexpensively via package delivery companies (UPS or refrigerated trucking firms) on a national basis. For instance, a large percentage of whip production occurs in Oregon, yet whips are distributed throughout the United States. This is possible because whips are a relatively small tree, generally unbranched or lightly branched, and shipped bareroot, which allows high density packing in the truck. Although national distribution potential is appealing from a sales perspective, it requires knowledge of the national market.
Most growers in Georgia produce finished trees and sell to landscape contractors, landscape developers, or municipalities. Based on the Market Channel Map, Georgia growers have several opportunities to expand their product line. Whips are a product with numerous avenues of distribution and one of increasing demand. However, most of the whips utilized or planted in Georgia are purchased from Tennessee or Oregon. Local growers could improve whip quality supplied from the Southeast and sell on a local, regional, or national basis. The market opportunity for top quality whips is significant.
Opportunity also exists within the state to produce high quality liners. The quality of a finished tree is significantly influenced by the liner quality. Most liners in the state are either produced by the finisher or bought from Florida or Tennessee. Application of state-of-the-art forestry and ornamental nursery practices can result in better quality liners than are currently available.
From the Market Channel Map, we see there are several opportunities to expand the product line for tree growers in Georgia. Once the target product and customer group is selected, the next step is to interview individual potential customers. The objective should be to conduct a preferred supplier survey. In this survey, you can determine specific varieties, specifications, and service requirements. You should also visit your customer's customer to determine trends and needs that your customer will be addressing. The presence of quality liner and whip producers in Georgia would greatly enhance the finished tree industry in this state. It would give finishers a local, ready supply of good quality material. The opportunity also exists to grow liners and whips of those products that are native or perform well in the southeastern United States. In some cases, these products are not produced as easily or as well in the Pacific Northwest.
Deciding which plants you should grow can be a difficult decision. Information can be gained by talking with landscape architects, university personnel, landscapers, garden center managers, plant brokers, and other nurserymen. Attending trade shows and looking through trade publications and nursery catalogs is also a good idea. Some of the more common shade trees being produced in Georgia nurseries include ash, river birch, maple, oak, sweet gum, sycamore, tulip poplar, and willow. Popular flowering trees include cherries, crape myrtles, crabapples, dogwoods, flowering pears, and redbuds. According to a recent survey by the National Landscape Association, the following shade and flowering trees were ranked as the most popular in the Southeast (Alabama, Delaware, Florida, Georgia, Kentucky, Maryland, Mississippi, North Carolina, South Carolina, Tennessee, Virginia and West Virginia):
| Shade Trees | Flowering Trees |
| Red maple | Callery pear |
| Willow oak | Flowering dogwood |
| Pin oak | Crabapple |
| Sugar maple | Crape myrtle |
| Honey locust | Oriental cherry |
| Red oak | Yoshino cherry |
| Japanese zelkova | Kousa dogwood |
| River birch | Eastern redbud |
| Live oak | Southern magnolia |
| Norway maple | Flowering plum |
Other trees that should be considered in Georgia would include shumard oak, scarlet oak, sawtooth oak, nuttall oak, fringe tree, saucer magnolia, sweet bay magnolia, upright hollies, ginkgo, Japanese pagoda tree, sourwood, and black gum. Remember that a grower should produce plants that are adaptable to their climate and production system while considering the suitability of a given plant to the target market area.
Seed source is an important factor to consider if choosing tree seedlings. Select seed from sources that are adapted to the area in which the seedlings will be grown. For example, redbud from southern seed sources is not winter hardy in the northern part of its range, whereas seedlings from the northern part of the plant's range will not perform well in the southeastern United States. The forest products industry has done much selecting and dividing of species by provenance, ecotype, seed lot, clones, and families to assure that trees are adapted to their intended growing sites. This has not been done on a large scale for most of our ornamental tree species.
Another problem associated with using seedling material is seedling variation. The genus Quercus is notorious for hybridizing naturally. Because oaks are wind pollinated, seedlings grown from a given tree vary. More than 100 different oak hybrids have been documented in the United States and Canada. A visit to the sand ridges in the coastal plain of Georgia will convince one of the great degree of variability found within different species of oaks. Recent work at the University of Georgia has shown that some species of oak (willow, English, and overcup) can be successfully rooted. Vegetative propagation procedures are needed in order to make clonal selections of outstanding specimen plants for production and introduction into the landscape trade.
Tree liners can also be purchased as vegetatively propagated plants. Examples would be plants grown from cuttings, grafted plants or plants that have been tissue cultured. There is a great deal of interest in plants grown on their own roots from vegetative cuttings. Southern magnolia is an excellent example of a plant in which production has been improved through the use of vegetative cuttings. Walk into any nursery and you can immediately pick out a block of seedling-grown magnolia plants due to variations in size, stem straightness, leaf color, etc. Several new vegetatively propagated southern magnolia selections are available that offer many desirable characteristics compared with seedling-grown plants. Certain cultivars of red maple have been found to have a bud union incompatibility problem, which results in tree loss due to stem breakage at the bud union. This problem can be overcome by growing red maples on their own roots.
Another problem associated with rooted cuttings is overwinter survival. This problem has been documented in the following genera: Acer, Betula, Cornus, Corylopsis, Hamamelis, Magnolia, Rhododendron, Stewartia, and Viburnum. Research has shown that budbreak prior to overwintering, stored carbohydrate levels, and photoperiod may all affect survival of rooted cuttings during the first winter after rooting.
Crabapples are another example of plants that may benefit from growing on their own roots as compared with grafting. When crabapples are grown on their own roots, they have been reported to produce fewer suckers (this is variety dependent). However, the use of clonal apple rootstocks has been shown to decrease suckering, decrease problems associated with poor anchorage and have root hardiness similar to own-root plants.
Several species of trees are now available as tissue-cultured liners. Examples include Amelanchier, several species of betula, Chinese or lacebark elm, Cladrastis or yellow wood, flowering crabapples, flowering cherries, Franklinia, Tilia or linden, and several selections of red maple. Advantages of tissue culture plants include increased vigor and uniformity and the ability to propagate otherwise difficult-to-root species. As a result of tissue culture procedures, numerous selections of Kalmia or mountain laurel, a previously difficult-to-propagate plant, are now readily available. Tissue culture plants are generally available as rooted microcuttings and liners. There has been very little research on the growth and performance of tissue cultured plants compared to traditional methods of propagation. Research from Tennessee has shown that container-grown tissue culture liners of red maple and river birch can be transplanted into the field seven to 10 weeks after sticking microcuttings in a greenhouse.
Production Procedures and Purchase Criteria for Quality Liners
The production of quality liners is the critical first step in the ultimate goal of quality in-ground finished shade trees. The term liner refers to the 1-0 bareroot seedling as described in the first section of this document. Unfortunately, sufficient attention is generally not provided to the quality of liners produced or purchased. This section details production steps that can produce quality liners. The information will also enable liner customers to assess the quality of liners and quiz suppliers on production techniques.
The first step in liner production is selection of the production site. The soil should be loose and well aerated at all times during production. Well-aerated soil is critical to good root development, the primary objective of liner production. Therefore, high sand content is desirable, although the extreme of pure sand should be avoided. It is sometimes suggested that it is okay to use heavy soils for hardwood production because hardwoods grow in poorly drained soils with high clay content. However, it is important to distinguish between what a plant will tolerate versus what is necessary to produce a quality root system. Typical bottom land soils will not produce the root system associated with quality liners. Aerated soils are just as critical for hardwood seedlings as for conifer seedlings such as loblolly and slash pine. The ideal site allows surface water runoff, percolation of rainwater and irrigation, and does not have a shallow hard pan that can hinder development of the root system.
Seed bed preparation affects the germination percentage and the uniformity of seedling emergence. The seed bed is generally fumigated prior to planting. Methyl bromide, under a plastic covering, is an effective way to eliminate weed seed and pathogens. When using methyl bromide, exercise caution and carefully follow label procedures. Methyl bromide application can decrease the level of mycorrhizae, which, in turn, can affect the performance of seedlings. The higher the moisture content during fumigation, the more complete the kill of mycorrhizae. There is a tradeoff between elimination of all weed seed and pathogens and the need to have some mycorrhizae present for hardwood seedlings. The soil should be thoroughly rototilled and elevated. The equipment to form seed beds is readily available. It is virtually impossible to do a good job of root pruning or wrenching if the seed bed is not elevated. Also, the elevated bed provides a well aerated medium for root system development.
To get uniform seedling emergence and spacing, it is important that all seeds germinate, and germinate at essentially the same time. State-of-the-art seed sorting and grading procedures should be used prior to sowing. The more commonly used grading techniques include flotation sorting, which removes empty seeds. Newer techniques developed for bedding plant production include seed priming. Seed priming is the process whereby seeds start germination and proceed to essentially the same stage of germination prior to sowing. Primed seeds emerge sooner and with less variation between seedlings. Uniform seedlings also require uniform spacing and depth of sowing. Sowing machines are available for coniferous seed but not for hardwood seedlings. Each nursery will have to adapt existing sowers to get reasonable spacing and depth of sowing of the seed. Seed can be sown in 4- or 6-foot-wide beds with several rows of trees. The advantage of individual rows is the ability to prune the root system laterally during production.
Time of sowing is another factor that affects uniformity. With oak seed, many people sow the acorns in the fall as soon as harvested. The alternative is to hold the seed until the next spring. The problem with fall sowing is that the seed is subjected to more variation in weather conditions resulting in greater variation in seedling emergence. The primary reason for fall sowing is for convenience. However, even with storage-sensitive oak seed, if the proper moisture level is maintained during storage, excellent germination can be achieved. Seed production and handling is a vast and complex subject. For additional information on the topic, nurserymen should consider the valuable reference by the USDA: Seeds of Woody Plants in the United States, Agriculture Handbook No. 450.
Once the seedlings have emerged, several cultural practices are necessary to control growth and produce uniform seedlings. Generally within weeks after seedling emergence, it is important to undercut the root system. Undercutting is achieved by use of a narrow, sharp blade to cut the tap root. If this process is initiated soon after seedling emergence, the number of laterals that develop will be enhanced. Because the primary objective of the liner stage is root system development, it is critical to undercut early. This is especially true for tap root plants such as oaks. In fact, some people have resorted to cutting of the radicle prior to sowing. This is not necessary and is more costly than early undercutting. Done properly, the undercutting process will not disturb the seedlings or severely hinder early growth. With many seedlings, the undercutting process should be repeated two or three times during the growing season, increasing the depth of cutting by about 2 inches for each successive cut. In this way, you are continually pruning the tips of new roots.
Water management during the growing season is another tool to control height and caliper. It is also essential due to selection of a well-drained site. The withholding of water in late summer and early fall will slow top growth and favor caliper and root development. However, be careful to avoid severe water stress, which can cause extensive leaf damage or defoliation. This is an area that will require more research to quantify the relationship between plant water status and subsequent growth.
The fertilization of hardwood seedlings in the nursery bed is an area that requires further study. In general, we can start with the incorporation of a well-balanced preplant fertilizer. This is complemented with liquid feed or dry fertilizer broadcast during the growing process. It has been reported that the addition of micronutrients during the growing cycle enhances plant color and growth.
Wrenching during the growing cycle is an effective method to control height growth. Wrenching is accomplished by use of a thick bar that is run underneath the root system at a slight angle. The objective is to raise and loosen the soil around the roots. In doing this, you break the contact of the soil and root tips resulting in a complete root pruning. The aeration and root pruning causes increased water stress and will slow down the top growth. This process will increase the number of lateral roots and increase caliper. This is a useful, seldom utilized, technique for controlling height growth that should be practiced by more growers. There is no set frequency of wrenching. Use wrenching to control height growth, root system, and caliper as you monitor the crop.
Production and research results indicate that top pruning can increase the uniformity and caliper of conifers and hardwood seedlings. However, risks are associated with top pruning. In many of the pines, the plant will readily develop one dominant shoot, and you will not see the effect of top pruning. Top-pruning hardwoods can result in two or three shoots. This is undesirable for seedling production. If the seedlings are used as understock, then it is not as critical because you will sever the top after one year of growth. Another risk is that top pruning will delay bud set in the fall, which can delay the optimum time for lifting. Another concern with top pruning is that you allow weak, low-vigor seedlings to catch up to the high-vigor seedlings. These low-vigor seedlings may show up as smaller plants in the next stage. Growers should try to achieve uniform seedlings by means other than top pruning. This includes seed bed preparation, uniform seedling emergence, undercutting, water management, and fertilizer practices.
Performance of liners can be evaluated in terms of survival and early growth. Although the target liner has not been described for deciduous seedlings, there are several important characteristics. Whip growers can use these characteristics as purchasing criteria. The target seedling characteristics include:
In summary, the most important factor for a top quality liner is a well-developed lateral root system. The trunk and branches can be modified in subsequent cultural practices more readily and to a greater degree than can the basic root system. Corrective action at the next stage of production also requires more time and expense.
Liner Quality and Impact on Subsequent Practices
The quality of the starter material has a significant impact on subsequent plant quality, performance, and cost. If you start with the premise that as a tree grower you can rarely improve on the quality of plants purchased, then it is important to start with the best available liner.
Quality as applied to liners can be divided into two aspects: physical and physiological. Typically, the target liner is described in terms of physical attributes. These attributes include caliper (stem diameter at ground level), height, root system, and stem morphology.
The most desired caliper is ¼ inch or larger. Uniformity across seedling liners is very important to achieve a uniform crop of whips. The caliper of the liner will affect the vigor of the grafted bud after cutback. Even in the case of seedlings, caliper will influence subsequent growth and can result in height variations. Therefore, the target caliper and consistency of caliper across seedlings is important to a uniform crop.
Height is a widely used physical attribute but difficult to assign a single quantitative value. The appropriate height will vary by variety -- oaks being different than redbuds. Generally, a ¼ inch caliper seedling will be in the range of 12 to 24 inches. As long as the height is in proportion to the caliper and root system, the seedling will perform well.
A well-developed root system is another important attribute and the major objective in growing of liners. A good root system will have four or five major laterals and numerous small feeder roots that are still viable and not dried out. Avoid the large single "carrot" tap-root system because a large portion of the root system will be left in the seedling nursery during lifting, resulting in lower survival and early growth.
Another important physical attribute is the existence of a dormant terminal bud at the time of lifting. If the plant is starting to flush or has not set bud, survival will decline rapidly with storage. Even with unstored trees, survival will be lower than trees with a dormant bud. The absence of a terminal bud could also be an indicator that it has been removed. The result will be multiple terminal shoots, an undesirable feature when the goal is a single straight stem.
Physiological attributes are important to liner performance but are not as well defined as the physical attributes, particularly for hardwood seedlings.
Water status of the seedling can be quantified and is important to transplant performance. Generally, the greater the water stress at time of lift, or after storage, the lower will be survival and early growth. However, there is a need for specific guidelines that relate levels of water stress during handling and subsequent performance. This will allow the liner customer to use water status as a quantitative measure of seedling quality.
Another important physiological attribute is the seedling root regeneration potential. The root regeneration potential is a predictor of the quantity and rate of root development after transplanting. It is possible to have two seedlings, similar in appearance, with very different quantities of roots after the first year. Factors that affect root regeneration potential including fertilization prior to lifting, stage of dormancy at lifting, and duration of storage.
The third physiological attribute important to seedling performance is the stage of dormancy at time of lifting. The stage of dormancy can be described as the hours of chilling temperatures (32° to 54°F) the seedling is exposed to prior to lifting. Research with loblolly pine demonstrated a relationship between hours of chilling temperature prior to lift, duration of storage, and the out-plant performance. Quantitative guidelines do not exist at this time for hardwood seedlings. Based on loblolly pine research, hardwood seedlings should have 200 to 400 hours of chilling temperatures before lifting and storage. These seedlings will generally have better survival and early growth. The seedlings can be stored for at least 12 weeks at about 40°F in Kraft-polyethelene bags.
After purchase of the liner, the buyer has several responsibilities to ensure that the quality of the liner is maintained such as:
The purchase of high quality liners requires that you understand the physical and physiological status of the plant. Proper handling techniques must then be employed to maintain seedling vigor during post harvest handling.
It is important for the liner customer to work closely with the liner producer. Orders should be placed one year in advance so the producer can develop a seedling with the appropriate physical and physiological attributes.
It is often tempting to save a few pennies on liners by purchasing lower quality seedlings. Investment in a top quality liner, particularly a good root system, will be paid back several fold in terms of lower cost and improved quality. The impact of a poor root system on subsequent cultural practices includes:
In summary, the few additional pennies required to buy the best quality liner will easily be paid back several fold in reduced growing cost. In addition, performance in the consumer's operation will be enhanced.
The second stage product for in-ground tree production is referred to as whips (Figure 3). The emphasis for this stage of production is the development of uniform, straight, branch-free trunks of 3 to 5 feet prior to branching.
The production process starts in the spring of year one. At that time, bareroot liners are planted in-ground at an approximate spacing of 15 inches within the row and 48 inches between rows (Figure 3). The apparent high density is possible because the objective is a tree with straight stem and minimal branching.
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| Figure 3. One-Year Whip Production |
The liner (cuttings or seedlings) is allowed to grow during the first year. Toward the end of the first growing season, grafted varieties are budded. For instance, with red maple varieties the liner would be a seedling of Acer rubrum. In the summer of the first year, it is budded with the desirable variety (Red Sunset, October Glory, Autumn Blaze, etc.). If the plant is to be grown as a seedling, (dogwood, redbud, etc.) grafting is not required. Typically, during the first year, there is minimum root pruning. This is due in part to the larger plant material making it more difficult and expensive to root prune. However, plants could certainly benefit from lateral pruning and early undercutting of liners placed in the whip beds to enhance further development of the root system.
In the early spring of the following year, year two, the plant is cut back. Generally it is best to cut back prior to bud expansion. If it is a budded variety, the top is cut to just above the bud. The new shoot develops as temperatures warm in the spring. If the plant is not grafted, it is cut back to about ground level. Several shoots will emerge in early spring. The most vigorous shoot is retained and all others removed. Immediately after emergence of the shoot, support is supplied to the emerging shoot. Items such as Tree Straights™, which resemble spatulas, are placed in the ground next to the new shoot. The support prevents breakage of the succulent shoot by wind and development of a crook in the stem. Selection of shoots on the windward side also minimizes wind breakage in early spring.
Plants can be staked after emergence of the new shoot in the spring of year two. A metal stake is placed in the ground adjacent to the new shoot, and the shoot is tied to the stake with plastic straps every 2 to 3 inches. This requires frequent tying of trees during the growing season and is important to achieve a straight trunk.
During the second year after transplanting, first year growth of the scion material, major branches that emerge on the lower part of the trunk, are either removed or cut back to three or four leaves. The objective is to remove branches that might compete with the terminal or form a narrow crotch angle. At the same time, we want as many leaves as possible on the plant to enhance stem caliper. Premature removal of leaves will reduce stem caliper.
In the fall of year two, the stakes are removed. During that following winter, the whips are harvested as bareroot plants. Commercial harvesters are available that undercut the root system and lift the trees so they can be handled as bareroot trees. The trees are placed in large open-end boxes and placed in cold storage. In the Pacific Northwest, some growers heel-in the bareroot whips in the outdoors. However, in the South, cold storage capacity units are required. The whips are then graded and packed during the winter and prepared for shipment the next spring.
A review of the one-year whip production scheme shows that a one-year whip requires two years from the liner stage. The "one-year" in one-year whip refers to the production time required after the shoot is cut back. The finished product has a 3-year-old root system (including the liner production stage) and a one-year top, hence the term one-year whip. "Whip" refers to the straight stem with minimal branches, an instrument synonymous with discipline in previous generations.
A frequently asked question about whip production is, "Why wait until the second year to cut back the plants?" The first year of growth at the whip stage is to allow extensive root development prior to cutting back. The root system and carbohydrate reserves are necessary to force extensive shoot growth in one year. In this way, you can achieve 5 to 8 feet of straight stem growth in one year. The smaller liner trying to overcome transplant shock is not likely to achieve such growth. This is important since the objective is to achieve sufficient stem growth for the branch-free trunk of the new tree. The other reason for maximizing height growth is that whips are sold by height as well as caliper; i. e., the taller the tree the higher the price. While most trees will produce 4 to 6 feet of straight, branch-free stem in one-year, oaks usually require two years after cutback. However, the uniformity of stem straightness across the crop is greatly enhanced over trees not cutback. Also, there are plastic devices that attach to the first and second year shoot and enhance stem straightness.
In addition to the training described above, another important cultural practice is maintaining a weed-free environment. Rototilling between the rows controls weeds, keeps soil well aerated, and provides some degree of root pruning. Herbicides can be applied in a 6- to 12-inch band at the base of the trees to control weeds close to the plant material. Irrigation is applied overhead or, in most cases, as trickle irrigation. With the high plant density, most of the water and fertilizer is intercepted by the root system.
In-ground tree producers in the Southeast, except for Tennessee, have overlooked the possibility of producing whips. The overall quality of finished trees in the Southeast could be improved with the production of quality whips. This would allow production of straighter, more uniform plants, and give the growers additional marketing opportunities. Another reason for increased production in the Southeast is to provide a source of whips of native plants that cannot be produced in the Northwest. Weather and soil conditions make it difficult to produce the same quality whip as is produced in the Northwest. However, Georgia growers could produce a better quality whip than is currently available from the Southeast and focus on plants native to our region. The good news is that demand in the Southeast will be for plants that are native or adapted to this area. Additionally, the whip-size trees are increasingly popular with container nurseries and municipalities. The whip fits the needs of municipalities since it is an inexpensive tree (compared with specimen trees) yet of sufficient size to impact the landscape immediately.
Finished Trees: Production Systems
In Georgia, there are more than 5,000 acres of field-grown nursery stock in production. For a finished tree, the goal is to develop a straight-trunked tree with a well-developed canopy. Depending on the final size of the tree produced, this can take anywhere from two to seven years.
Traditionally, field-grown nursery stock has been dug by hand with a spade. The root balls were covered with burlap and sold B&B trees. There are several advantages to digging trees B&B compared with other methods. Because B&B trees can be dug and held for limited periods of time, the digging and transplanting season is extended. When compared with trees dug bare-root, difficult-to-transplant species often transplant better when dug B&B. Because the tree has an intact root ball with native soil, transplanting shock due to poor soil water movement, as is often seen with container-grown material, is minimized.
Most conventionally grown nursery stock in the Southeast is now harvested with a mechanized tree spade. Generally, trees greater than 1¼ inch in caliper, which require an 18-inch root ball, are mechanically harvested. Tree spades are available in a variety of sizes that will dig root balls from 15 inches to greater than 40 inches. The American Association of Nurserymen (AAN) provides standards for root ball diameter in relation to trunk caliper. This book is available from the AAN for a nominal fee. Mechanically dug trees are placed into burlap-lined wire baskets for transport to holding areas before the trees are sold.
Trees harvested B&B or with a tree spade have some potential disadvantages. Often a large portion of the root system is removed when the tree is dug, which is thought to decrease the rate of establishment in the landscape. This can be minimized by root pruning during field production. The availability of trees can be limited by weather conditions and growth patterns. The winter or during the plant's dormancy is the easiest time for digging trees. However, with proper precautions, trees can be dug essentially all year with the exception of spring flush. Time of digging can be limited by soil moisture conditions. The root balls of trees dug B&B or with mechanical diggers are awkward and very heavy. Trees dug B&B require a considerable labor force that is skilled in this harvest method.
Smaller trees can be harvested bare-root. Advantages to producing bare-root trees for harvest are that the plants are lightweight, which makes shipping more economical. The initial cost per plant is low, and this low cost can be passed on to the consumer. A major disadvantage to digging trees bare-root is handling problems and field survival. Short periods of exposure to environmental extremes during the digging process can damage fine roots, which are important for transplant survival.
Root-control bags or Gro-bags were developed in the early 1980s and offer an alternative method for the production of field-grown trees. A Gro-bag is a cylinder made of porous fabric with a plastic bottom that prevents the formation of difficult-to-harvest tap roots. The porous fabric sides serve two purposes: first, to allow for the movement of moisture in and out of the bag; second, to confine the roots within the bag. Using conventional methods of harvesting, up to 80 percent of the root ball may be removed from a tree at the time of digging. The idea behind the root-control bag is that 80 percent or more of the roots will be harvested.
Gro-bags offer some advantages at harvest. Because more of the root system is present at the time of digging, there should be less transplant shock and increased survival. The possibility of digging field-grown trees in Gro-bags during the summer also exists because of the greater proportion of intact roots. If trees are harvested during the growing season, this should be done between flushes of growth when the tree has had a chance to set new buds and harden off. For those species that grow continuously throughout the season, a hardening-off period will be required. Special attention should be given to decreasing evaporative demand and regeneration of the root system during the hardening period.
Another advantage of Gro-bags is that two men can dig a 2-inch caliper tree in approximately one-fourth the amount of time required to dig a B&B plant. Also, no expensive tree-digging equipment is required. A recent report from Missouri indicated that harvesting of Gro-bags could be increased 1,000 fold by utilizing a backhoe for harvesting compared with conventional hand digging.
To date, there have only been a few studies looking at the growth of nursery trees in Gro-bags. All indications are that responses to Gro-bags are very species dependent. While Gro-bags offer an alternative to traditional production practices, all the potential problems of this production system are not known. Some of the known problems include:
A relatively new innovation in the area of field production is the pot-in-pot concept. With the pot-in-pot system, a holder pot is placed in the ground with the lip of the pot remaining above grade. A planted container of similar size is then placed inside the holder pot, thus a pot in a pot. Some benefits of this system are protection of the root system from extreme temperatures, less plant blowover, and other advantages associated with harvesting and marketing a container-grown tree. Plants with vigorous root systems such as crape myrtles root out through drainage holes into the surrounding soil, which makes harvesting difficult. Other problems with the pot-in-pot production system have been poor drainage in heavy soils, lack of support for the planted container, holder pot settling, breakage of staked plant,s and plant damage when trees are harvested during the heat of the summer. Further research is required before the pot-in-pot production system can be recommended on a large scale.
Field-grown trees are normally dug during the dormant season when there is less potential transplant stress. However, the summer digging of trees has become a common practice. Caution must be taken when handling summer-dug trees. Trees full of leaves will rapidly lose water through transpiration when most of the roots that provide water will have been severed. In general, trees that are not flushing should be dug during the early morning hours when plants are turgid and moved to a shaded area with overhead irrigation for seven to 10 days to cut down on moisture loss while new roots regenerate. Water loss can also be reduced by stripping leaves from trees.
Variability in climatic conditions and reoccurring dry summers during the 1980s has shown the need for supplemental irrigation of field-grown trees in Georgia and the Southeast. Supplemental irrigation is very important during the transplanting and establishment phase and has been shown to affect the survival and growth rate of trees. Properly irrigated nursery stock will be more vigorous and larger in a shorter period of time, thereby reducing the time required for nursery tree production cycles.
Three methods, in addition to experience, which can be used to schedule irrigation of field-grown trees are:
Tensiometers are used to measure the soil water tension and reflect the relative moisture content of a soil. Most tensiometers are calibrated to read from 0 to 100 centibars and can be used effectively in the 0 to 80 centibar range. Tensiometer readings of 0 to 10 centibars indicate that the soil is nearly saturated, while readings in the range of 10 to 20 centibars indicate that the soil is at field capacity. Irrigation should begin when tensiometer readings are between 20 to 50 centibars, depending upon the sensitivity and age of the trees being grown. In sandier soils, which have a lower water holding capacity, it may be necessary to begin irrigating when tensiometer readings are between 15 and 20 centibars. Readings of 70 centibars and greater will begin to result in tensiometer failure and indicate that available water is below the threshold required for optimal plant growth.
Electrical resistance blocks work by measuring the electrical resistance or flow of electricity between wires imbedded in gypsum or nylon. The blocks are placed in the soil, and, as the soil dries, the resistance block loses moisture and resistance increases. The change in resistance is related to the moisture content of the soil. The electrodes in the blocks are connected to wires that can be attached to a portable meter for readings. All resistance blocks require calibration to different soil types. Because blocks are manufactured by different companies, each manufacturer should supply calibration curves for their own meters and blocks.
Generally, a shallow block and a deep block are used to schedule irrigation applications. For example, if trees have an active root zone depth of 18 inches, then a shallow block should be placed at 8 inches with the deep block at 12 inches. On sandy soils, irrigation should begin at 25 centibars; irrigation may not need to be started in a clay loam soil until a reading of 40 centibars is reached. Stop irrigation when the deep resistance block indicates a wet condition (10 to 20 centibars). Readings should be taken three times weekly to prevent drastic changes in soil moisture content.
Various researchers have attempted to base irrigation requirements for nursery stock on daily evaporative demands. This methodology may be suitable if accurate correction factors for plant size can be utilized. The following generalized table is useful for determining drip irrigation rates (gallons/acre/day) in the Southeast:
| Pan Evaporation (inches) | Percent Canopy Coverage of Ground | ||||||
| 10 | 20 | 30 | 40 | 50 | 60 | 70 | |
| 0.33 | 343 | 686 | 1029 | 1370 | 1713 | 2057 | 2400 |
| 0.22 | 228 | 458 | 686 | 914 | 1142 | 1371 | 1600 |
| 0.11 | 114 | 228 | 343 | 457 | 571 | 686 | 800 |
Daily pan evaporation rates are usually determined at weather stations in your area. The county Extension office should be helpful in finding where this information can be obtained. If pan evaporation rates are not available, then use the 0.33 scale during very hot, dry weather, the 0.22 scale during warm weather and the 0.11 scale during mild weather.
Determining when to water is an acquired skill that can be aided by using some of the methods described above. The primary goal of irrigating trees is to provide supplemental water so as to prevent soil moisture stresses that lead to suppressed tree growth.
While overhead irrigation has been the traditional method of irrigating container nursery stock, advances in drip irrigation technology in recent years makes drip irrigation a viable alternative. Overhead or sprinkler irrigation is wasteful in that aisles and roads also get watered. It has been estimated that drip irrigation can reduce water consumption by 75 percent and water runoff by as much as 90 percent. A reduction of 75 percent in water consumption and energy costs would greatly benefit a grower's operation.
Drip irrigation has a number of advantages and disadvantages. The main advantages are decreased labor and operating costs; increased application efficiency; fertilizer application through the system; limited surface wetting of the ground, which reduces weed populations; fewer foliar diseases due to decreased wetting of leaves; no wind effect on water application, allowing it to occur 24 hours a day if needed; and use of smaller pipe sizes and pumps. Other advantages of drip irrigation systems include easy adaptation to automatic control, reduced pollution and runoff potential, and increased infiltration rates in difficult-to-wet soils. Research has shown that plants grown under drip irrigation have a greater number of roots concentrated in the rootball zone. This could be an important consideration for difficult-to-transplant species.
Some of the disadvantages of drip irrigation systems are as follows: the water supply needs to be clean or expensive filtering systems are required; drip emitter clogging can occur due to algae, poor water filtration or various chemicals in the water; rodents and other animals may chew on irrigation pipes; inadequate water distribution may occur on sandy soils due to lack of lateral water movement; and drip line shifting may occur due to wind and cold or hot weather contraction/expansion. This next to last problem can be compensated for by using multiple emitters or by using low volume, specific area spray emitters.
The most common types of drip systems used are:
Disposable drip lines are generally useful for one year. Where long drip irrigation lines are required or when lines are placed on uneven terrain, pressure-compensating drip emitters should be used to prevent variation in irrigation application.
Fertilization of field-grown nursery stock in Georgia is one area where very little research information is available for making recommendations. Currently, many fertilization recommendations are based on research conducted in other states with different soil types and climatic conditions. Steps that should be taken in order to implement a nursery fertilization program are to determine your soil type(s), have soil tests performed, interpret soil test recommendations, and make corrective applications of fertilizers before planting nursery stock.
In Georgia, there are eight major soil associations that can be divided into three major categories:
Coastal Plain soils occur roughly in the southern half of the state and include the Atlantic Coast flatwood soils and the Sand Hill regions in the middle of the state. These soils are characterized by sandy surface layers with relatively low nutrient holding capacities. Piedmont soils are generally acidic, well-drained red soils that are naturally low in phosphorus but which have a greater nutrient-holding capacity because of their increased clay content. The Mountain and Valley soils occur in the northern part of Georgia and are generally low in inherent fertility and vary in textural qualities.
The key to successful soil sampling is to get a representative sample from a given field of nursery stock. This can often be complicated by the fact that different parts of a field may have different soil types, slope, drainage and other management considerations. A composite of 15 to 20 soil cores (4 to 8 inches deep) should be taken for each field. Areas to avoid when taking soil samples include field borders, areas next to roads, old fertilizer bands, eroded areas and places where materials such as mulch or brush have been stockpiled.
Once a soil test has been made, nutrients such as phosphorus, potassium, calcium, and magnesium are incorporated before nursery stock is planted. The desirable pH for most Georgia soils is 5.5 to 6.0. The amount of lime required to raise the pH of nursery soils is calculated on the basis of a lime requirement (L.R.). The L.R. is a comparison of the soil water pH to the soil buffer pH. Recommendations for liming rates can be found in the Soil Test Handbook for Georgia (Georgia Cooperative Extension Service). Guidelines for soil test interpretations of phosphorus, potassium, calcium, and magnesium are shown in Table 1.
Tissue analysis of nursery stock can also be used to monitor nutrient accumulation and plant nutritional status. Late summer or early fall sampling is particularly useful because the spring flush of growth will be dependent upon nutrient accumulation during the previous year. Uniform sampling of recently matured leaves is very important for meaningful tissue analysis. Approximately 20 to 30 leaves per acre of plants should be collected for a representative sample. All leaf samples should be healthy, free of disease and insects and should be taken from plants that are not under stress. Residue on leaves should be removed with distilled water before drying samples. After sending samples to a commercial testing laboratory, the following guidelines can be used to interpret elemental tissue analysis (percent of leaf dry weight) for the uppermost leaves of woody ornamental plants:
| Nitrogen | 2.0 - 2.5 percent |
| Phosphorus | 0.2 - 0.4 percent |
| Potassium | 1.5 - 2.0 percent |
| Calcium | 0.5 - 1.0 percent |
| Magnesium | 0.3 - 0.8 percent |
Current recommendations for nitrogen fertilization of field-grown nursery crops in the state of Georgia range from approximately 100 to 300 pounds of nitrogen per acre per year. For all nursery crops, a preplant application of 50 pounds. N/acre is recommended. Nitrogen should be applied at planting if not incorporated at the preplant stage. For established trees in the production phase, the following rates are applicable. Deciduous trees generally require the highest rate of nitrogen (220 to 270 pounds N/year/acre) followed by narrowleaf evergreens (175 to 220 pounds N/year/acre). Broadleaf evergreen plants are often fertilized at the rate of 90 to 140 pounds N/year/acre.
Rate and timing of nitrogen application will depend on soil type and location in the state. For example, many growers in Florida are applying 300 pounds N/year/acre in six applications plus liquid feeding once per week while growers in Tennessee are applying 200 pounds N/year/acre in two applications with no supplemental liquid feed. Clay soils have a greater capacity for nutrient retention compared with the sandy loam soils in the southern part of the state and therefore may require less frequent applications and less total fertilizer.
Because root growth begins before shoot growth in the spring, nitrogen fertilizer application should occur approximately four to six weeks before spring budbreak for established plants. In North Georgia, this may be in the latter part of February. Nitrogen fertilizer should be put out in split applications which can range from two (North Georgia) to six (South Georgia) applications. Slow-release forms of nitrogen can be used to increase uniformity of feeding and decrease nitrogen losses although this form of fertilizer is much more expensive than regular release formulations. Fertilization timing will again depend on your operation and your location in the state.
Various methods exist for applying fertilizer to field-grown nursery stock. Two common methods are banding and broadcast. While most fertilizers traditionally have been applied using a rotary broadcast spreader, banding has been shown to decrease the amount of fertilizer applied and is very practical during the first two years of tree growth. Injection of fertilizer or fertigation has gained in popularity in recent years. Fertigation has several advantages in that nutrients are concentrated in the root zone, which helps to localize the root mass and cut down on weed problems associated with overhead irrigation. Fertigation also allows for the regular application of nutrients, which provides a more steady rate of feeding, thereby resulting in accelerated growth. In South Georgia, fertigation should begin in late February and should end in September. For North Georgia, the process should begin in March and stop in August. Total pounds of nitrogen applied may actually be reduced using fertigation practices because timing can be scheduled and the fertilizer is applied directly to the root zone. Growers can check with other growers in their area in order to find out what works and to determine the most cost efficient way to fertilize field-grown nursery crops.
Table 1. Georgia soil test interpretations for phosphorus, potassium, calcium and magnesium on ornamental crops.1
| Soil Group | Phosphorus Test Level Pounds/Acre | ||
| Low | Medium | High | |
| All Soils | 0 - 50 | 51 - 100 | 100 - 200 |
| Soil Group | Potassium Test Level Pounds/Acre | ||
| Low | Medium | High | |
| All Soils | 0 - 150 | 151 - 250 | 251 - 450 |
|
|
Calcium Test Level Pounds/Acre | ||
| Low | Adequate | ||
| Coastal Plain | 0 - 200 | 201 + | |
| Piedmont, Mountain and Valley | 0 - 400 | 401 + | |
| Soil Group | Magnesium Test Level Pounds/Acre | ||
| Low | Medium | High | |
| Coastal Plains | 0 - 60 | 61 - 120 | 121 + |
| Piedmont, Mountain and Valley | 0 - 120 | 121 - 240 | 241 + |
1 See the Soil Test Handbook for Georgia (Georgia Cooperative Extension Service) for more information.
Production Systems: Weed Control
Weed control is a major concern for producers of field-grown nursery stock. While the control of weeds has traditionally been handled with physical or cultural means, increased labor costs and advances in herbicide technology now make the use of herbicides a viable alternative. All nurseries should have a weed control program that combines the benefits of both herbicides and traditional weed control methods.
A variety of cultural and physical weed control methods are available for control of weeds in field-grown nursery stock. To begin, always use weed-free seed sources and planting stock. Weed infested transplant material can only add to your weed control problem and may actually introduce new weed species to your nursery. Crop rotation and use of cover crops may also benefit your weed control program. Good stands of clover in the summer and ryegrass in the winter effectively choke out competing weed species.
Methods of physical weed control include pulling, hoeing, mowing, and mechanical cultivation of weeds. Mowing is used primarily to prevent weeds from going to seed and for maintenance purposes. Repeated mowing is one way to discourage the growth of tall weeds. Mechanical cultivation is a good method for controlling the growth of annual weeds. In general, cultivation does not provide good control of perennial weeds unless the perennial weed seedlings are very small or repeated cultivations deplete the stored carbohydrate pool in established weeds.
Chemical control of weeds involves the use of weed killing chemicals known as herbicides. Herbicides are available in a variety of formulations and are abbreviated as follows: E or EC, emulsifiable concentrate; G, granular; L, flowable; AS, aqueous suspension; and W or WP, wettable powder. The formulation that one uses will depend on the target weed, equipment to be used (e.g., WP products need to be agitated), and economics as well as other factors.
Herbicides fall into three different classifications based on their intended use:
Few post-emergent herbicides are labeled for field-grown nursery stock. Labeled herbicides and their recommended uses can be found in the Georgia Pest Control Handbook. Contact your county Extension agent for assistance. It is imperative that nurserymen obtain the label for each of the herbicides (or any pesticide) and follow label instructions. This information is developed to ensure safe and effective use of pesticides.
Chemicals that are applied to the soil in order to eliminate pathogens, insects, nematodes, and weed seeds are known as soil fumigants. Soil fumigants are generally used when no other alternatives are available for difficult-to-control weeds. Due to the high value of certain ornamental crops, use of soil fumigants is often economically feasible. However, fumigants such as methyl bromide are being regulated out of use.
Most soil fumigants are most effective as gases and therefore are influenced by a variety of factors, most notably soil temperature, soil moisture content, and the physical condition of the soil. For effective control, the soil should be friable, well aerated, and free of clods. Adequate soil moisture should be available for weed seed or propagule germination. As a general rule, soil temperatures should be between 55° and 85°F at a depth of 5 to 6 inches. A successful weed control program will consist of a well-defined plan along with the appropriate use of physical, cultural, and chemical controls. Proper sanitation and control of existing weeds are necessary for an effective weed control program.
This bulletin covers many of the key areas that are important to the production and marketing of field-grown shade trees. If you are considering the startup of a tree production operation, it would be beneficial to spend time understanding your market and potential customers prior to a major commitment of capital. While there are many aspects to startup and operation of a tree nursery, it is important to maintain a balance between production and marketing activities. Many people enter the business because they like to grow trees! You only make money when you successfully grow and market trees. Shade tree production requires a substantial upfront investment. The production time can be lengthy. With this scenario it is imperative to target the right cultivar, size and form of tree to enhance market acceptance. Other considerations as a business owner or manager would include federal and state labor regulations, pesticide use regulations, and development of a business plan to secure financing. Your county Extension agent can be a resource to provide necessary information.
An Equal Opportunity Employer/Affirmative Action Organization Committed to a Diverse Work Force
Bulletin 1115, July 1999
Issued in furtherance of Cooperative Extension work, Acts of May 8 and June 30, 1914, The University of Georgia College of Agricultural and Environmental Sciences and the U.S. Department of Agriculture cooperating.
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