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This Journal of Environmental Horticulture article is reproduced with the consent of the Horticultural Research Institute (HRI www.hriresearch.

1 This Journal of Environmental Horticulture article is reproduced with the consent of the Horticultural Research Institute (HRI which was established in 1962 as the research and development affiliate of the American Nursery & Landscape Association (ANLA HRI s Mission: To direct, fund, promote and communicate horticultural research, which increases the quality and value of ornamental plants, improves the productivity and profitability of the nursery and landscape industry, and protects and enhances the environment. The use of any trade name in this article does not imply an endorsement of the equipment, product or process named, nor any criticism of any similar products that are not mentioned. Copyright, All Rights Reserved

2 Effect of Copper-Treated Containers on Transplant Survival and Regrowth of Four Tree Species 1 Daniel K. Struve 2 Department ofhorticulture, Ohio State University Columbus, OH Abstract Northern red oak (Quercus rubra L.), scarlet oak (Q. coccinea Muenchh.), sweetgum (Liquidambar styraciflura L.), and 'Autumn Flame' red maple (Acer rubrum L.) liners were produced in copper-treated (100 gm Cu(OH)211 white latex paint) or untreated black plastic 3.8 I containers (Lerio C-700) in In spring 1990, liners were transplanted into field plots. Half the liners produced in untreated containers were root pruned just before transplanting, half were not. Liners grown in copper-treated containers were not root pruned before transplanting. Survival percentage was high for ~ll species ranging from 92% for red maple to 65% for scarlet oak. Three years after transplanting, red and scarlet oak liners produced in copper-treated containers had higher survival rates (but not statistically significant) and greater regrowth (taller, greater trunk caliper and percent central leader formation) than liners produced in untreated containers, whether root pruned or not before transplanting. Regrowth of red maple and sweetgum were not affected by container type used during liner production. The study demonstrates species differences to transplanting; each species responds to transplant via a unique combination of growth characteristics. Transplant responses are expressed up to three years after transplanting. Index words: establishment, urban forestry Species used in this study: Northern red oak (Quercus rubra L.); scarlet oak (Q. coccinea, Muenchh.); sweetgum (Liquidamber styraciflura L.); 'Autumn Flame' red maple (Acer rubrum L.). Significance to the Nursery Industry High quality nursery stock can be produced in coppertreated containers. Red and scarlet oak grown in coppertreated containers have greater survival and regrowth potential than plants grown in untreated containers. Root pruning container grown red and scarlet oak at transplanting to correct possible root system defects, inhibits shoot growth the second growing season after transplanting. Red maple and sweetgum growth are unaffected by container type for the first three years following transplanting. Root pruning red maple and sweetgum at transplanting does not affect early growth and many not be necessary. However, possible long-term effects-are unknown. Plant survival was not positively correlated with regrowth after transplanting; red maple had the highest survival rate, but the least amount of shoot growth. If the definition for plant establishment is: shoot growth recovering to pre-transplant amount, then none of the plants in this study have become established during the three year study. Introduction Container-grown nursery stock offers several advantages over field-grown stock. However, there are some disadvantages to container produced nursery stock of which root system malformation is potentially the most serious. Root system malformation has many causes (12) and is expressed by multiple symptoms in various combinations (3, 13, 20). Root system malformation can be corrected at planting by several root pruning methods (4, 11). The most severe methlreceived for publication June 25, 1993; in revised fonn September 7, This research was supported in part by grants from the Ohio Nurserymen's Association; the Horticultural Research Institute, 1250 I Street, N.W., Suite 500, Washington, DC; and the Griffin Corporation. 2Associate Professor. 196 ods remove a significant proportion of the root system (1). Most root pruning methods result in short term growth reduction (2, 7, 8, 10). Copper-treated containers can control root malformation and increase transplant survival and regrowth (1, 5). Several studies have shown the benefit of producing plants in copper-treated containers compared to plants produced in untreated containers which were root pruned at planting to correct root malformation. However, no study has compared post-transplant growth of liners produced in untreated containers which were either root pruned or not before transplanting with growth of liners produced in copper-treated containers. This study compares growth during liner production and after transplanting of three coarse-rooted species, (red and scarlet oak, and sweetgum) with growth of a fibrous rooted species (red maple) grown in copper-treated and untreated containers. Liners grown in untreated containers were either root pruned or not before transplanting to determine the effects of root pruning or regrowth. Materials and Methods In fall 1988, red and scarlet oak seeds were collected from trees on The Ohio State University campus, placed in plastic bags and stored at 4 C (40 F) until germinated in March Sweetgum microcuttings were produced in the Horticulture tissue culture lab, rooted and grown to 15 cm (6 in) height by fall The sweetgum plants were stored overwinter in a polyhouse. 'Red Sunset' red maple rooted microcuttings purchased from Microplant Nurseries, Inc., Gervais, Oregon in February In March, 1989, seeds were sown or microcuttings potted in copper-treated (100 gm CuC0 3 /1 white latex paint applied to interior container surfaces) or in untreated 3.8 I (Lerio C-700) round black plastic containers. In May, the plants were moved outdoors and up canned. Plants grown in treated containers during the greenhouse phase were up canned into J. Environ. Hort. 11(4): December 1993

3 Table l. Percent (%) survival three years after field planting for red and scarlet oak, sweetgum and'autumn Flame' red maple. Root Container pruning Number Percent Species treatment Z treatmenty planted survival Red oak Untreated Untreated Copper-treated Scarlet oak Untreated Untreated Copper-treated Sweetgum Untreated Untreated Copper-treated Autumn Flame' Untreated Red maple Untreated Copper-treated ZPlants were grown in either untreated or copper-treated containers, 100 gm CuC03/l white latex paint. YPlants grown in untreated containers were either root pruned (+) by making three vertical slashes equally spaced around the I:oot ball or not (-) before transplanting. Plants grown in copper-treated containers were not root pruned. similarly treated 114 I (Lerio C-1050) black plastic coppertreated containers; plants grown in #1 untreated containers were up canned to untreated #3 containers. All plants were grown under Ohio Production System conditions (16) during Plants were over wintered in an unheated double layer inflated poly house. In April 1990, the plants were transplanted to a former agriculture field on the OSU campus. The plants were planted in two soil types: Crosby silt loam or Kokomo silty clay loam. Half of the plants grown in untreated containers were root pruned (three vertical slashes equally spaced around the root ball 2.5 cm (1 in deep) the other half were not. Plants grown in copper-treated containers were not root pruned before planting. Thus, there were three treatments for each species. The plants were planted in a completely random design. The numbers ofplants per species and treatment are given in Table 1. After planting, all plants were mulched with 5 cm (2 in) of hardwood bark in 1 m (ca. 3 ft) diameter circle. The plants were not irrigated after planting and received minimal after care; the site was mown three times per year with no additional weed control. Plant height was measured at planting and annually each fall until 1992 for red and scarlet oak and sweetgum. For the red maples, shoot extension on three lateral branches was measured and averaged. In September 1990 and 1992, trunk caliper was measured on all plants. The data for each species were subjected to analysis of variance using SPSS/PC+ (15). Means were separated using the Student-Newman-Keuls test at an alpha level of Results and Discussion Plants grown in untreated containers had roots concentrated at the growing medium/container wall interface and were considered pot bound. Plants grown in copper-treated containers showed limited signs of circling root development and little root development near the medium/container wall interface. In the nursery, growth for all species was rapid. For instance, red maple averaged 2.5 m (10 ft) in height (Table 3). Height growth of scarlet oak was greater in copper-treated containers than in untreated containers in 1989 (Table 2). For the other species, there were no significant differences in growth attributed to container type. Transplant survival was high for all species, no less than 65%, despite minimal after care and two years with below normal rainfall during the growing season (1990 and 1991) (Table 1). For red maple, red oak and sweetgum, there were no differences in survival percentages among the treatments (Chi Square tests were not significant at alpha = 0.05 level). For scarlet oak, survival percentage among liners of the three treatments was significantly different (alpha level 0.05); liners grown in copper-treated containers had the highest survival percentage. In 1990, the first season after transplanting, red oaks grown in copper-treated containers were taller than those grown in untreated containers and root pruned at transplanting (Table 2). By 1992, plants grown in untreated containers and not root pruned at planting were significantly shorter than plants grown in copper-treated containers. Three years after transplanting (1992), red oaks grown in copper-treated containers had greater trunk caliper than plants grown in untreated containers, whether root pruned or not. Table 2. Three year field growth for red and scarlet oak, sweetgum and'autumn Flame' red maple. Height (em) Caliper (em) Container Root pruning Species treatment Z treatmenty Red oak Untreated 112a w 166ab 175a 188b 1.2a 2.0b Untreated + l04a 154b 178a 192ab 1.2a 2.1b Copper-treated 120a 180a 195a 212a 1.2a 2.5a Scarlet oak Untreated 92b 138b 164a 188b 1.1a 1.7b Untreated + 93b 130b 159b 176b 1.2a 1.6b Copper-treated 118a 179a 200a 219a 1.2a 2.4a Sweetgum Untreated l09a 155a 177a 219a 1.2a 2.8a Untreated + 127a 171a 190a 220a 1.2a 2.8a Cooper-treated lila 147a 173a 215a 1.2a 2.7a ZPlants were grown in either untreated or copper-treated containers, 100 gm CuC03l1 white latex paint. YPlants grown in untreated containers were either root pruned (+) by making three vertical slashes equally spaced around the root ball or not (-) before transplanting. Plants grown in copper-treated containers were not root pruned. WMeans within a species and column followed by different letters are significantly different from each other at a alpha =0.05 level using Student-Newman Keuls test. J. Environ. Hort. 11(4): December

At all measurement times, scarlet oak grown in coppertreated containers were significantly taller than plants grown in untreated containers (Table 2).

4 At all measurement times, scarlet oak grown in coppertreated containers were significantly taller than plants grown in untreated containers (Table 2). For liners grown in untreated containers, root pruning had no effect on growth after transplanting. By 1992 trunk caliper was greater for plants grown in copper-treated containers than for plants grown in untreated containers. Neither container type, nor root pruning treatment had any effect on sweetgum growth before or after transplanting (Table 2). In 1990, red maple average lateral shoot length was significantly greater for non-root pruned liners grown in untreated containers than for plants grown in copper-treated containers or for plants grown in untreated containers and root pruned before transplanting (Table 3). There were no differences among the treatments in lateral shoot growth in 1991 and Overall, 1992 red maple lateral shoot length was four times greater than in Shoots measured in 1992 were vigorous trunk sprouts formed after extensive die back of the central leader; one half to two thirds of total plant height was lost during the winter. The greatest frequency of die back, 83%, occurred for plants grown in untreated containers and not root pruned (Table 3). There were no differences in caliper size. Red oak and scarlet oak liners produced in copper-treated containers were twice as likely to maintain a central leader after transplanting, as liners produced in untreated containers, whether root pruned or not (Table 4). All red maple and sweetgum liners n1aintained a central leader after transplanting (data not presented). In this study growth was characterized by measuring survival percentage, amount of shoot growth, percent of trees with a central leader and stem die back. The combination of post-transplant growth characteristics differed for each species. For instance, red maple had a high survival rate, 920/0, but the poorest regrowth after transplanting. Lateral shoot elongation averaged near 50 cm in 1992, but the vigorous shoot growth occurred after a majority of the plants suffered significant central leader die back. Prior to the winter, red maples maintained a central leader, despite limited shoot growth. In contrast, transplanted scarlet oaks expressed a different combination of regrowth characteristics. Scarlet oaks had the lowest average survival percentage (76%), moderate shoot growth, (annual three year average of 31 cm (12 in)), suffered no die back, but had high rates of central leader loss. Finally, red maple growth was little affected by container type or pruning treatment, while scarlet oak grew better if produced in copper-treated containers. The shoot growth data in this study and in Watson, et al. (18) illustrate the limitations of making recommendations based on the first year's growth in a transplant study and the danger of extrapolating results from one species to other species. Shoot growth for red and scarlet oak was greater in 1990 than in 1991 and Sweetgum shoot growth was less in 1991 than in 1990, but recovered in 1992 to 1990 an10unt. Red maple lateral shoot growth was limited until the, central leader was lost during the winter. Typically, the first season's growth after transplanting is more a reflection of the previous year's growing conditions than an indication of long term regrowth potential. A good definition of when a plant becomes established after transplanting is when shoot elongation resumes to pretransplant an10unt (18). By this definition, none of the plants have become established during this three year study. Plants may never become "established" because vigorous growth produced under new cultural systems (16) cannot be duplicated in nursery or landscape sites. Perhaps, "established," with reference to recovery from transplanting needs to be modified. The four species also differed in the ability to maintain a central leader after transplanting. For red and scarlet oak, the ability to maintain a central leader was affected by cultural conditions; liners produced in copper-treated containers were twice as likely to maintain a central leader as liners produced in untreated containers. In contrast, all red maples and sweetgums, regardless of production conditions and shoot growth vigor, maintained a central leader after transplanting. Sweetgum, even when shoot pruned, will reestablish a central leader (14). Transplanting field grown (14) and container stock (1) can result in significant root loss. Ifshoot growth vigor is related to degree of root loss at transplanting and rate of root system developn1ent after transplanting (2, 17), then it is clear that red and scarlet oak produced in copper-treated containers have higher root growth potential than plants grown in untreated containers, whether root pruned or not at transplanting. One aspect of a malformed root system is reduced shoot vigor as expressed by low foliage density, twig and branch die back and death (3, 13, 20). This study shows that high quality nursery stock may not perform well when transplanted, not because of too vigorous growth during production, but rather because of malformed root systems left uncorrected at planting. Root system malformation is n10st readily induced and most easily corrected in the early production stages (12). Copper-treated containers would be valuable in early stages of production. Table 3. Average laterial shoot growth and percentage of individual 'Autumn Flame' red maple plahts suffering die back in Container treatment Z Root pruning treatmenty Average laterial shoot length (cm) Caliper (cm) % individuals with die back in 1992 Untreated Untreated Copper-treated a w 17.8b 18.5b II.4a II.4a 9.9a 46.5a 51.5a 52.8a 3.0a 3.0a 2.8b 4.0a 4.0a 3.9a ZPlants were grown in either untreated or copper-treated containers, 100 gm CuC03l'1 white latex paint. YPlants grown in untreated containers were either root pruned (+) by making three vertical slashes equally spaced around the root ball or not (-) before transplanting. Plants grown in copper-treated containers were not root pruned. wmeans within a species and column followed by different letters are significantly different from each other a alpha =0.05 level using Student-Newman-Keuls test. 198 J. Environ. Hort. 11(4): December 1993

5 Table 4. Percent of red and scarlet oaks that have a well defined central leader three years after transplanting. Root Container Pruning Presence of Species Treatment Z Treatmenty central leader (%) Red oak Untreated 38b w Untreated + 30b Copper treated 60a Scarlet oak Untreated 40b Untreated + 35b Copper treated + 62a ZPlants were grown in either untreated or copper-treated containers, 100 gm CuC03/1 white latex paint. YPlants grown in untreated containers were either root pruned (+) by making three venical slashes equally spaced around the root ball or not (-) before transplanting. Plants grown in copper-treated containers were not root pruned. wmeans within a species and column followed by different letters are significantly different from each other a alpha = 0.05 level using the Chi Square test. Some species may 'not need to be root pruned to correct putative root malformation as species differ in the rate of development and effects of root malformation (3, 6, 13,20). Further, transplanted red maple can form a new root system via adventitious root formation at the root collar after transplanting (19). Other species likely to possess this characteristic, and thus may not need root pruning at transplanting, are flood plain species such as sweetgum. However, this study reports short term results; possible long term effects are unknown. Therefore it is not prudent at this time to recommend that container-grown plants of flood plain species not be root pruned at planting. Growing plants in copper-treated containers may inhibit girdling root development in ways other than preventing circling root development during production. Watson, et al. (18) hypothesized that root pruning field grown nursery stock during the course of production and harvest may stimulate girdling root development by releasing lateral roots that are growing at right angles to the main root axis (a common condition). Plants grown in copper-treated containers usually do not require root pruning to correct root malformation; therefore, girdling root development resulting from lateral roots is less likely to occur. Literature Cited I. Arnold, M.A. and D.K. Struve, 1989a. Growing green ash and red oak in CuC03-treated containers increases root regeneration and shoot growth following transplant. J. Amer. Soc. Hon. Sci. 114: Arnold, M.A. and D.K. Struve, 1989b. Green ash establishment following transplant. J. Amer. Soc. Hon. Sci. 114: d'ambrosio, R.P Crown density and its correlation to girdling root syndrome. J. Arboriculture 16: Blessington, S.c. and M.N. Dana Post-transplant root system expansion in Juniperus chinesis L. as influenced by production method, mechanical root disruption and soil type. J. Environ. Hon. 5: Burdett, A.N Control of root morphogenesis for improved mechanical stability of container grown lodgepole pine. Can. J. For. Res. 8: Ellyard, R.K Effect of root pruning at time of planting on subsequent root development of two species of eucalyptus. J. Arboriculture 10: Geisler, D. and D.C. Ferree Response of plants to root pruning. Hon. Rev. 6: Gilman, E.F. and M.E. Kane. 1990a. Growth and transplantability of Magnolia grandijlora following root pruning at several growth stages. HonScience 25: Gilman, E.F. and M.E. Kane. 1990b. Root growth ofred maple following planting from containers. HonScience. 25: Gilman, E.F Effect of root pruning prior to transplanting on establishment of southern magnolia in the landscape. J. Arboriculture 18: I I. Gouin, F.R Girdling by roots and ropes. J. Environ. Hon. 1: Harris, R.W., W.B. Davis, N.W. Stice and D. Long Influence of transplanting time in nursery production. J. Amer. Soc. Hon. Sci. 96: Holmes, F.W Effects on maples of prolonged exposure by anificial girdling roots. J. Arboriculture. 10: Hummel, R.L. and C.R. Johnson Influence of pruning at transplant time on growth and establishment of Liquidambar sytracijlua L., Sweet Gum. J. Arboriculture. 4: Norusis, MJ SPSSPC+ V2.0 base manual. SPSS Inc., Chicago, Ill. 16. Struve, D.K. and T. Rhodus Turning copper into gold. American Nurseryman 172(4): Watson, G. W Root regeneration of transplanted trees. J. Arboriculture 8: Watson, GW., E.B. Himelick, and E.T. Smiley Twig growth of eight species of shade trees following transplanting. 1. Arboriculture 12: Watson, G.W. and T.D. Sydnor The effect of root pruning on the root system of nursery trees. J. Arboriculture 13: Watson, G.W., S. Clark and K. Johnson Formation of girdling roots. 1. Arboriculture 16: Environ. Hort. 11(4): December

ROOT SYSTEM CONFIGURATION AFFECTS TRANSPLANTING OF HONEYLOCUST AND ENGLISH OAK

129 JOURNAL OF ARBORICULTURE June 1989 Vol. 15, No. 6 ROOT SYSTEM CONFIGURATION AFFECTS TRANSPLANTING OF HONEYLOCUST AND ENGLISH OAK by D.K. Struve, T.D. Sydnor 1 and R. Rideout 2 Abstract. Eight cm (approximately