REDUCING TREE LOSS IN THE LANDSCAPE REQUIRES THE COOPERATION OF NURSERY PRODUCERS, LANDSCAPE INSTALLERS, AND MAINTENANCE PERSONNEL

Transcription

1 REDUCING TREE LOSS IN THE LANDSCAPE REQUIRES THE COOPERATION OF NURSERY PRODUCERS, LANDSCAPE INSTALLERS, AND MAINTENANCE PERSONNEL By T. Davis Sydnor School of Natural Resources The Ohio State University Nursery production practices can and do influence the performance of plants once they are in the landscape. A problem that has been causing problems for years but has been more recently identified, as being of particular concern is the landscape problems and losses resulting from plants being harvested too deep in the rootball. It is difficult for the green industries to understand the problem or their role due to the segmentation in the green industry. I was fortunate when I was employed in the nursery industry to work for a full service nursery. We took the cuttings, raised the cuttings to liners, lined them out in the field, grew them to saleable size, designed and sold clients landscape, installed the landscape, and then frequently maintained the plants in the landscape after planting. A failure anywhere along the line could more easily be spotted and corrected. Today a different company completes each production function and they are often in different states. While segmentation results in more efficient production it also makes it especially difficult to identify problems that happen early in the production cycle since information does not readily flow back up the supply chain. The owner of a dead or dying plant may well be faced with a group of green industry professionals each pointing at someone else and claiming that the other person or the property owner is responsible for the loss. The norm is to blame the last guy in the door. When I mentioned this problem to a nurseryman a few years ago he joked, I don t care about that. If the plant dies, I sell a replacement plant. The implication was that it was good for business to sell nonviable plants. This cavalier attitude ignores the fact that the owner has choices. He/she can buy a replacement plant or a bass boat or a trip to Cancun or whatever else they desire. The green industry s competition is 1

2 really any industry that competes for disposable income, not other nurseries. I will now get down from the soapbox that I have been on. Let s consider the problem of plants being too deep in the rootball. I will define the problem, discuss how it may occur, consider if it is common enough to be a concern, consider the landscape implications, discuss ways to address the problem, and consider the potential benefits. I. THE PROBLEM The problem begins with planting specifications. The following diagram (Figure 1) is taken from a text that I use in teaching landscape management (Sydnor, T. D. 2003). I will use this illustration to make the point without pointing fingers. This diagram is consistent with the ONLA standards adopted in 2000 except that this illustration only requires 6 inches between the ball and the side of the hole rather than the 9 inches required by ONLA standards. I do not intend to discuss the controversy regarding the shape or size of the hole. Figure 1. Planting of a balled and burlapped tree. Drawing was done by Jay Duecaster. The problem arises in the fact that the specifications were prepared with the assumption that the plant is being dug with the first order lateral roots at the top of the rootball and that the excess soil has been removed. The first order lateral roots are the primary support roots for the tree. Tap roots abort quickly in many species but function as secondary support in others. Figure 2 shows two maple seedlings. The first order lateral roots are already forming in these month-old seedlings. The soil line is at the base of the crook formed as the seedling began to grow upright from a seed that is lying on the soil surface. Note that the first order lateral roots are formed about an inch below the soil line as is typical of Ohio trees including silver maple. The lateral roots are the primary means of nutrient and water uptake. Figure 2. Two seedling silver maples (lots this year) showing first order lateral roots. The taproot is seen in the right plant but has already been lost in the left seedling. 2

3 pervasive. All plants that I reviewed were between 1 and 12 inches too deep with an average of four inches of excess soil on the first order roots (Figure 3). When the first order roots are several inches too deep the plant responds as if it were buried too deeply as you would imagine. Stem girdling roots can form in the excess soil, which is devoid of first order lateral roots. Some floodplain species such as such as green ash can root and establish another root system above the older root system. Figure 3. A surveyors chaining pin rests on the first order lateral root 9-10 inches below the top of the rootball. The landscape installer does not realize that the plant is being planted too deep. II. HOW IT MAY OCCUR Several factors or practices in the nursery can result in the plant being dug too deep in the rootball. 1. The plant can be planted too deep when it is lined out either inadvertently or to reduce the need for staking. 2. Rototilling or cultivating during the first few years can throw additional soil against the stem. 3. The plant can be purposely planted too deep to hide the bud crook. Digging crews can forget or be pressured into neglecting to remove the excess soil from the top of the ball when they are harvesting with a tree spade. Also remember that a 32inch tree spade does not dig a 32-inch rootball unless the frame of the tree spade is set below grade. Collected trees and conifers are less likely to suffer from this concern. Collected trees are generated from seed in place. Conifers are known to require shallow planting and excess soil thrown against the main stem will damage and destroy the lower foliage and make the plant less valuable. Figure 4. A group of 3.5-inch Callery pears in a holding area purchased from an Ohio grower. Ball size ranged from 31 down to 24 inches in diameter when ANSI Z60.1 standards called for a 38-inch rootball. The net result from any of the above is that the first order roots are too deep in the rootball. The impact of adding soil over the root system is well known. As little as 4 inches of soil over the root zone can kill some trees (Sydnor and Heiligmann 1999). III. FREQUENCY Nursery producers, when talking with me, indicate that they always instruct crews to remove the excess soil before digging. In contrast, Robin Hunt (2003) estimates that all trees that they purchased were too deep in the rootball when received. As I inspected trees at four sites from a variety of growers, I found that the problem was 3

4 IV. LANDSCAPE IMPLICATIONS Rootball width at various depths - Rootball width has been shown to be the critical measure in a study of rootball size when rootball volume was held constant (Struve et al 1989). The rootball may also be below ANSI standard width at the first order root depth if excess soil is above the first order roots even if the rootball is dug with an ANSI standard rootball. Table 1 shows the relationship between depth to first order roots and rootball width at that depth. Table 1. The relationship between depth to the first order roots in the first column and rootball width for ANSI standard rootballs for trees between 2 and 3.5-inch caliper. Depth to 2" caliper 2.5" caliper 3" caliper 3.5" caliper Roots Tree Tree Tree Tree Table 1 makes the reasonable assumption that the cross-section of the rootball is an isosceles triangle before the excess soil is removed from the bottom. As can be seen, the greater the depth to the first order roots the smaller the width and/or diameter of the rootball. Since the rootball width is the cr4ritical dimension, it would be expected that the tree would have a reduced survival rate when compared with a tree with an ANSI standard rootball width. Functional rootball volume at various depths Rootball volume is another consideration although related to rootball width of course. Volume is probably the best way to understand the impact since volume is a function of the radius cubed. The rootball can be described as a hemispheroid. Volume is described as 2 / 3 πr_ * d where r = rootball radius and d = rootball depth. Table 2. Unshaded rootball volumes are related to a 38-inch standard rootball for a 3.5-inch tree. Shaded areas below are related to the standard rootball size for a 2- inch tree. Standard ANSI rootball diameters are in bold for reference. ANSI Ball Ball % Volume % Larger Standard Width Volume Reduction Required % 0% % 118% % 140% % 167% % 203% % 250% % 312% % 397% % 0% % 130% % 173% % 237% % 338% An example from Table 2 is that a 34-inch ball diameter is 28% smaller than the volume of a standard 38-inch rootball and would have to be 140% larger to be standard sized. From Table 1 one can see that a 34- inch rootball would result from a 38-inch rootball dug a little less than 4 inches too deep in the ball. Note that impacts are more severe on smaller 24-inch rootballs than for larger 38-inch rootballs. 4

5 Increased planting costs The City of Cincinnati has requested that excess soil be removed from the rootball for the last two years (Hunt 2003). This will be formalized into the bidding specifications beginning this fall. This requirement is also being incorporated into the specifications for all trees planted as a result of urban forestry grants beginning this fall (Todd 2003). I estimate after talking with several landscape contractors, that the cost of removing excess soil will require ten minutes per tree or 20 man minutes for a crew of two. At a common rate of $60 per hour this results in an added cost of $20 per tree for planting. Increased costs can be absorbed by a combination of increasing costs for consumers, reducing profit for landscape contractors and reducing the numbers of trees being planted. Figure 5. A tree planted on Cincinnati, OH streets with excess soil removed. Stem girdling roots Stem girdling roots cause a slow decline of trees in the landscape. Death from stem girdling roots is often delayed for years or decades with death coming as the tree was beginning to have the desired effect in the landscape. Figure 7. A stem-girdling root exposed in excess soil above the first order root in an unplanted rootball. Figure 6. A close up of the above tree showing the excess soil removed. Six inches of soil was removed to the line. Figure 8. An 8 to 10-inch tree that failed in the Wooster shade tree evaluation plot. 5

6 The problem was severe enough in Norway maple that many cities eliminated Norway maples from their planting lists. Failure of graft union The reasons for graft union failures are not well understood. Genetics and contaminated graft unions are among the reasons given when explaining the situation. Some plants are less likely to develop this problem such as hawthorn while budding is rarely used to produce red maple because of graft incompatibility. Further graft unions buried in excess soil are exposed to contamination under conditions that favor disease development. Figure 9. Failure of a graft union that was hidden in the soil Instability during establishment Staking trees has become less popular during my thirty years in Ohio. The stability of a recently transplanted tree is dependent on the friction between the rootball and the adjoining soil. Thus anything that reduces the size of the rootball will reduce the stability of the tree. Rootball width is of particular concern. Of course guying and staking can be used to compensate for the reduced rootball size. Years ago I surveyed landscape contractors in Ohio to determine costs of guying and staking. Estimates for guying and staking ranged from percent of the planting costs. If a plant were displaced following planting the landscape contractor or property owner would be expected to stabilize the plant. Similarly, if a contractor consistently had trouble with displacement of plants that had not been staked, he/she would guy or stake. As before, costs could be covered by the property owner, landscape contractor, or by reducing the extent of the contract. Watering frequency- The frequency with which a plant must be watered is a function of the plant available water found in the rootball. It follows that if the rootball is too small either from being dug too small or from being dug too deep in the rootball, that the amount of water storage in the rootball would be reduced. From Table 1 we see that a 38-inch rootball that is dug 4 inches too deep would result in a 34-inch rootball and a 24-inch rootball 4 inches too deep would be a 20-inch functional rootball. From Table 2 we see that the 34-inch rootball would require watering 40% and a 20-inch rootball would require watering 73% more frequently that the ANSI standard 38 and 24-inch rootball required for a 3.5 and 2- inch tree respectively. Increased cost for additional watering would be borne primarily by the landowner and landscape maintenance contractor. Some additional costs would be incurred by the nursery industry as a result of additional costs incurred during holding and by the landscape contractors in the form of increased replacements. Increased stress related concerns Reduced rootball size results in greater transplant shock and increased losses due to secondary or stress related problems such as 6

7 borers. These problems often require time to kill the recently transplanted trees or increased maintenance in the form of pest control programs. Most commonly these hidden costs are born by the property owner and may include increased plant losses. These types of losses are most likely to result in a homeowner s frustration with gardening and a desire to spend money on a more enjoyable pastime. The green industry may not even know that they have lost a customer. failure. Urban foresters and urban landowners are charged with inspecting their trees to insure public safety. While the failure of these two trees did not cause personal injury, an 18-inch tree is certainly capable of doing so. Figure 11. Growth rings are marked in white and show no decrease in growth from the stem girdling roots prior to failure. Hidden defects When I was talking with a nurseryman earlier this year, he told me that he had to do that to hide the bud crook. Let us assume that the following example that is still emerging is the result of such a decision. Nine Urban elms were planted on the streets of Cincinnati (Hunt 2003) and have produced the scene seen in Figure 10. Figure 10. A 17-year old Urban elm planting on the streets of Cincinnati, OH. Figure 12. The swelling above the damage and stem girdling roots below the soil surface made the plant appear normal prior to failure. The extent of the defect and how well it was hidden is seen. Two of the nine plants failed this summer. These trees are now approximately 18-inch caliper. Failure of the trees caused only property damage. The growth rate of these trees certainly gave no clue that the trees were flawed (Figure 11). Growth rates were approximately an inch a year and are considered very fast. Such a hidden defect makes it difficult for the city forester to detect the flaw prior to 7

8 If personal injury were involved, it is likely that the city prosecutor would be looking for someone to share the blame. A city prosecutor would welcome a hidden defect (Figure 12). More likely the urban forestry program will have to incur costs associated with the inspection of the remaining 7 trees and the removal of trees with similar defects. Additional funds are unlikely to be provided by the city administration so the nursery and landscape construction industries will share in the cost through reduced tree planting budgets in Cincinnati. V. SOME WAYS TO ADDRESS THE PROBLEM A. Plant trees at the proper height during nursery production. B. Remove excess soil during harvesting. C. Landscape contractors should not accept or plant improperly dug plants. D. Landscape maintenance contractors could add excess soil removal as a customer service. VI. SOME BENEFITS OF ADRESSING THE PROBLEM A. Plants would grow more rapidly in the nursery. B. Nurseries would retain more topsoil. C. Planting costs would be reduced for the landscape contractor. D. Planting losses would be reduced. E. Watering costs would be reduced. F. Tree growth in the landscape would be accelerated. G. Landscape maintenance costs would be reduced. H. The service life of urban trees would be increased. I. The green industry would be viewed as being concerned about their customers J. The potential danger from flawed trees would be reduced in urban situations. K. Nursery consumers would enjoy more success and thus might be encouraged to plant additional material. VII. LITERATURE CITED Hunt, Robin Personal communication. Urban Forester, City of Cincinnati, OH. Johnson, Gary R. and R. J. Hauer A Practitioner s Guide to Stem Girdling Roots of Trees. U. of Minnesota Extension Service Bulletin BU 7501-S. 20pp. Struve, D. K., T. D. Sydnor and R. Rideout. l989. Ball size and shape affects transplanting of honeylocust and English oak. Journal of Arboriculture l5:l29-l34. Sydnor, T. D Natural Resources Landscape Maintenance, revised edition Grade A Notes, Columbus, OH, 235 pp. Sydnor, T. Davis and Randall Heiligmann Trees and Home Construction. Ohio State University Extension Bulletin #870. Columbus OH. 39 pp. Todd, Andrew Personal communication. Urban Forestry Coordinator, Ohio Department of Natural Resources, Division of Forestry. 8