Source: MICHIGAN STATE UNIV submitted to
IMPROVING TRANSPLANT SUCCESS OF CONTAINER-GROWN LANDSCAPE TREES: A COMPREHENSIVE APPROACH
Sponsoring Institution
National Institute of Food and Agriculture
Project Status
COMPLETE
Funding Source
HATCH
Reporting Frequency
Annual
Accession No.
1007897
Grant No.
(N/A)
Cumulative Award Amt.
(N/A)
Proposal No.
(N/A)
Multistate No.
(N/A)
Project Start Date
Dec 1, 2015
Project End Date
Nov 30, 2020
Grant Year
(N/A)
Program Code
[(N/A)]- (N/A)
Recipient Organization
MICHIGAN STATE UNIV
(N/A)
EAST LANSING,MI 48824
Performing Department
Horticulture
Non Technical Summary
Long-term survival of trees following transplanting in street tree or landscape plantings can be highly variable and is often an impediment to urban and community forestry programs. Failure of trees following transplanting may be related to an array of factors but often the underlying cause of transplant failures is transplant shock due to drought stress or poor root development. Losses of urban and suburban trees are highest among newly planted trees. Reducing the impacts of transplant stress on trees is often related to three key steps in the tree establishment process; nursery culture, planting, and maintenance after planting. Each step in the process may interact with the others to influence survival or growth. However, research in this field often focuses on a single step in the process at a time. For example, nursery studies typically determine the growth or other response of trees to a particular practice in the nursery but relatively few studies follow the trees through the planting and post-planting process to determine the ultimate long-term outcome of the practice.In this project we will examine long-term responses of trees to nursery culture, planting and maintenance in order to better understand the role of each step in tree survival and growth. We will examine innovative practices, such as root-shaving at planting and application of plant growth regulators in the nursery, on long-term performance of trees in landscapes. The results of this research will provide nursery managers, landscape contractors, and urban foresters with additional tools to improve the long-term success of landscape and street tree plantings.
Animal Health Component
75%
Research Effort Categories
Basic
15%
Applied
75%
Developmental
10%
Classification

Knowledge Area (KA)Subject of Investigation (SOI)Field of Science (FOS)Percent
1022110102025%
1242110102025%
1022110310025%
1242110310025%
Knowledge Area
102 - Soil, Plant, Water, Nutrient Relationships; 124 - Urban Forestry;

Subject Of Investigation
2110 - Ornamental trees and shrubs;

Field Of Science
1020 - Physiology; 3100 - Management;
Goals / Objectives
1) Evaluate the impact of nursery cultural techniques on physiology and morphology of nursery stock and subsequent transplant success2) Evaluate the impact of transplant techniques on transplant success of container grown trees3) Determine the impact of mulching after planting on long-term success of container-grown landscape trees
Project Methods
Over the next five years I will conduct a series of trials to address the objectives outlined above. Some of the trials will build on on-going studies; others will require the initiation of new experiments.Objective 1. Evaluate the impact of nursery cultural techniques on physiology and morphology of nursery stock and subsequent transplant success and Objective 3. Determine the impact of mulching after planting on long-term success of container-grown landscape treesIrrigation managementThis trial will utilize 48 Skyline honeylocust trees grown in 95 L (25 gal.) containers at the Pot-in-Pot research nursery at the MSU Horticulture Teaching and Research Center (HTRC). In summer 2016 half of the trees will be assigned at random to one of two irrigation treatments: Drought pre-conditioning and Control. Control trees will be irrigated daily with a sufficient volume to provide 10 to 20% leaching fraction, which is a common industry standard for irrigation of container nursery stock (Owen 2007; Fulcher and Fernandez 2013). We will withhold water from trees in the Drought pre-conditioning treatment for three drought cycles by capping the emitters in each tree container. We will measure pre-dawn water potential of the trees every other day during each drought cycle until the mean water potential reaches a target of -1.5 MPa (-15 bars). Once the water potential of trees in the drought pre-conditioned treatment has reached the target level, trees will be re-watered for two days and then the next drought cycle will commence. Following the final dry-down cycle trees from both treatments will be planted in a field block at the HTRC. All trees will be thoroughly watered immediately after planting. Half of the trees will be top-dressed with 8 cm (3") of ground pine bark mulch in a 60 cm (2') radius around the base of the tree to form a 2 x 2 factorial of drought preconditioning x mulching treatments. We will monitor trees for three years after planting. Assessments will include; tree survival, height and stem caliper growth, leaf water potential, and photosynthetic gas exchange.PGR treatmentIn spring 2014 we applied Paclobutrazol as a drench treatment to container grown conifers at Dutchman Tree Farm, Manton, MI. Treatments were applied to Norway spruce, eastern white pine and Serbian spruce in 11 L (3 gal.) and 19 L (5 gal.) containers. For each species and container size combination, 75 trees were assigned at random to one of three treatments; high rate of Paclobutrazol (200 ml), low rate of Paclobutrazol (100 ml) or untreated control (25 trees per treatment). The trees were grown in an operational block of container-grown trees in the pot-in-pot production area of the nursery.Growth assessments conducted in fall 2014 indicated that TGR applications significantly reduced growth for spruce but not for white pine. In spring 2016 we will plant 20 trees from each species x treatment combination in a field block at the MSU HTRC. A subsample of 5 trees per species x treatment combination will be harvested to assess root and shoot biomass and root:shoot ratio. Trees planted in the field block will be assessed for three years. Measurements will include survival, height and caliper growth, and photosynthetic gas exchange. At the end of the three years, five trees from each species x treatment combination will be harvested to determine root and shoot biomass and root:shoot ratio.Nutrient loadingIn spring 2006 we will initiate a new trial to determine the effect on nutrient loading of shade trees and subsequent out-planting performance. Bare-root liners (1.5 m (5') whips or lightly branched liners) will be obtained from a cooperating liner nursery. Species selection will depend on availability from the nursery but will include species commonly planted in Michigan. During the first year trees will be fertilized with a low rate of controlled release fertilizer (150 g Osmocote Plus 15-9-12 5 month release). Our previous experience indicates that this rate of fertilizer will provide adequate nutrition for tree establishment in the containers but will have little carry-over to the second year when we initiate the nutrient loading treatments (Klooster et al 2012). Prior to the start of the second year, three trees per species will be harvested to determine initial plant biomass and nutrient content. The remaining trees will be assigned to one of three treatments: Control (no additional fertilization), Conventional fertilization (High rate (400 g) of Osmocote plus) and Nutrient loaded. Nutrient loaded trees will be fertilized weekly using an exponential fertilization protocol as described by Salifu and Jacobs (2006). Nutrient loaded trees will be fertilized with a blend of water-soluble fertilizers (Peters Professional Products) to provide approximately the same balance of N-P-K as the controlled release product. We will measure height and caliper and SPAD chlorophyll index monthly during the growing season. We will collect leaf, fine root, and stem tissues for nutrient analyses in early August and prior to the leaf-fall. In the spring of 2018 we will plant the trees in the field block at the HTRC. Trees will be mulched after planting and watered once weekly for the first month after planting. Additional irrigation will be provided during the summer whenever the previous week's rainfall totals less than 2.54 cm (1"). Trees planted in the field block will be assessed for three years. Measurements will include survival, height and caliper growth, SPAD chlorophyll index, photosynthetic gas exchange, and foliar nutrient analyses.Objective 2. Evaluate the impact of transplant techniques on transplant success of container grown trees and Objective 3. Determine the impact of mulching after planting on long-term success of container-grown landscape treesRoot-ball shaving - Shade treesIn the spring of 2016 bare-root liners (1.5 m (5') whips or lightly branched liners) will be obtained from a cooperating liner nursery. Species selection will depend on availability from the nursery but will include species commonly planted in Michigan. Trees will be planted in 95 L (25 gal.) containers in an 80:20 v:v mix of pine bark and peat moss. The trees will be grown in the Pot-in-Pot nursery at the MSU HTRC for two years. Irrigation will be provided daily during the growing season and fertilization will follow the Conventional protocol described for the Nutrient Loading experiment above. In the spring of 2018, trees will be out-planted into a field block at the MSU HTRC. Prior to planting, trees will be assigned at random to one of two treatments: root shaving or control. For trees in the root shaving treatments we will remove the outer 4 cm (1.5") of the root-ball including the bottom using a pruning saw. Root-balls will not be disturbed for the control trees. All trees will be thoroughly watered immediately after planting and half of the trees will be top-dressed with 8 cm (3") of ground pine bark mulch in a 60 cm (2') radius around the base of the tree to form a 2 x 2 factorial of drought preconditioning x mulching treatments. We will monitor trees for three years after planting. Assessments will include; tree survival, height and stem caliper growth, leaf water potential, and photosynthetic gas exchange.

Progress 12/01/15 to 11/30/20

Outputs
Target Audience:Landscapers, arborists, urban foresters, homeowners. Changes/Problems: Nothing Reported What opportunities for training and professional development has the project provided?The project provided training andprofessional development opportunities for one M.S. graduate student (Riley Rouse) and size undergraduate students (Becky Pobst, Alex Love, Austin Wujkowski, Amber Feldpausch, and Elle Brandt. How have the results been disseminated to communities of interest?Results of the research have been disseminated to professional landscapers, arborists, and urban foresters through a series of presentations at state, national, and international meetings: Cregg, B. (2016) MSU Nursery Research Update. MSU Extension West Michigan Nursery Program, July 28, 2016. West Olive, MI. Cregg, B. and Stoven-O'Connor, A. (2016). Getting to the Root of the matter: Improving transplant success of container trees. International Society of Arboriculture Annual Conference. Aug.13-17, 2016. Fort Worth, TX. Cregg, B. (2016) The case for mulch. Michigan Nursery and Landscape Association Great Lakes Trade EXPO. Jan. 25-27, 2016.Lansing, MI. Cregg, B. (2016) What can tree growth regulators do for you? Arboriculture Society of Michigan Annual Conference. Feb. 9-10, 2016. Lansing, MI. Cregg, B. (2018). Improving transplant success of container-grown trees. Michigan Nursery and Landscape Association Great Lakes Trade EXPO. Jan. 22-24, 2018.Lansing, MI. Cregg, B. (2018). MSU Research update. Michigan Seedling Growers Association. Lake City, MI, Sept. 11, 2018. Rouse, R.P. Improving transplant success of container-grown trees: root shaving and bare-rooting. ISA Michigan Chapter. Oral presentation delivered at ArborCon 2020, Lansing, MI, February 2020. Cregg, B.M. & Rouse, R.P. Improving transplant success of container-grown trees: root shaving and bare-rooting. Michigan Nursery & Landscape Association. Oral presentation delivered at the 2020 Great Lakes Trade Exposition, Lansing, MI, January 2020. Cregg, B.M. & Rouse, R.P. Improving root systems of container-grown trees through pre-plant root modification: shaving and bare-rooting. Bartlett Tree Research Laboratories. Oral presentation delivered to the research staff at Bartlett Tree Research Laboratories, Charlotte, NC, August 2019. Rouse, R.P. Improving root systems of container-grown trees through pre-plant root modification: shaving and bare-rooting. International Society of Arboriculture. Oral presentation delivered at the 2019 International Society of Arboriculture Annual International Conference and Trade Show, Knoxville, TN, August 2019. Rouse, R.P. Improving root systems of container-grown trees through pre-plant root modification: shaving and bare-rooting. Arboriculture Society of Michigan. Oral presentation delivered at ArborCon 2019, Lansing, MI, February 2019. What do you plan to do during the next reporting period to accomplish the goals? Nothing Reported

Impacts
What was accomplished under these goals? We conducted two experiments to evaluate the impact of cultural treatments on growth and establishment of container-grown London planetrees (Platanus×acerifolia' Bloodgood'). In both experiments, 48 trees grown in 100 l (#25) black plastic containers were assigned at random to one of three root-ball treatments prior to planting; no treatment (Control), outer 3 cm of roots removed around entire root-ball (Shave), or outer circling roots disentangled from the root-ball (Tease). In Experiment 1, half of the trees were fertilized with 400 g of controlled release fertilizer (15-9-12; N-P2O5-K2O) at planting and the remainder of the trees were not fertilized. In Experiment 2, half of the trees were mulched with an 8 cm deep × 2 m diameter ring of coarse ground pine bark at planting and the remainder of the trees were not mulched. In Experiment 1, fertilization at planting increased SPAD chlorophyll content on two of four measurement dates but did not affect cumulative height or caliper growth after two years. After two growing seasons, root-ball treatments (shaving or teasing) increased root growth outside the original root-ball compared to control trees. Both root-ball treatments also reduced circling roots. In Experiment 2, mulching at planting increased soil moisture and cumulative tree height and diameter growth. Shaving increased new root growth and both root-ball treatments improved root architecture and reduced circling roots. Overall, the study demonstrates that root-ball manipulations can stimulate new root growth and reduce circling roots. Mulch is a valuable aid to conserve soil moisture and increase tree growth. Fertilization at planting provided little benefit in this experiment, which may have been related to a high level of soil fertility at the site or nutrient loading of the trees from nursery culture prior to transplanting. We conducted a second study to determine the effect of root modifications (shaving or bare-rooting) at planting on establishment, survival, and growth of container-grown Acer rubrum 'October Glory', Liriodendron tulipifera 'Fastigiatum', and Platanus x acerifolia 'Bloodgood'. Trees were planted on two dates (May and July) in 2018 and evaluated for two growing seasons. Modifying roots before planting increased subsequent leaf scorch for L. tulipifera and A. rubrum trees. Nearly all trees bare-rooted before planting in July had severe die-back. Survival was excellent (>87%) for all A. rubrum and P. x acerifolia trees planted in May regardless of treatment. Survival for L. tulipifera trees that were bare-rooted in May was 50%; all L. tulipifera trees that were bare-rooted in July died. Bare-rooting increased tree stress immediately after planting. However, leaf water potentials did not differ among root treatments for the rest of 2018 and throughout 2019. This suggests that trees with modified root systems achieved a functional equilibrium by adjusting leaf area to reduce whole-tree water loss. Root biomass outside the original root-ball did not differ among root modification treatments two years post-transplant. However, bare-rooting reduced the proportion of circling roots compared to control trees for all species. Shaving reduced circling roots compared to control trees for L. tulipifera and P. x acerifolia. For practitioners interested in trialing these techniques, we advise performing root modifications in the dormant season and avoiding species known to be difficult to transplant bareroot.

Publications

  • Type: Journal Articles Status: Published Year Published: 2018 Citation: Cregg, B., & Ellison, D. (2018). Growth and establishment of container-grown London planetrees in response to mulch, root-ball treatment and fertilization. Urban Forestry & Urban Greening, 35, 139-147.
  • Type: Journal Articles Status: Published Year Published: 2020 Citation: Poudyal, S., Owen Jr, J. S., Sharkey, T. D., Fernandez, R. T., & Cregg, B. (2020). Phosphorus requirement for biomass accumulation is higher compared to photosynthetic biochemistry for three ornamental shrubs. Scientia Horticulturae, 275, 109719.
  • Type: Journal Articles Status: Published Year Published: 2019 Citation: Poudyal, S., Fernandez, R. T., Owen, J., & Cregg, B. (2019). Dose-dependent phytotoxicity of pesticides in simulated nursery runoff on landscape nursery plants. Water, 11(11), 2354.
  • Type: Journal Articles Status: Published Year Published: 2020 Citation: Poudyal, S., Owen, J. S., Fernandez, R. T., & Cregg, B. (2020). Sensitivity of Hydrangea paniculata Plants to Residual Herbicides in Recycled Irrigation Varies with Plant Growth Stage. Water, 12(5), 1402.
  • Type: Journal Articles Status: Published Year Published: 2019 Citation: Poudyal, S., & Cregg, B. M. (2019). Workshop: Irrigating Nursery Crops with Recycled Run-off: A Review of the Potential Impact of Pesticides on Plant Growth and Physiology. HortTechnology, 1(aop), 1-14.
  • Type: Theses/Dissertations Status: Published Year Published: 2020 Citation: Rouse, R.P. 2020. Improving establishment of container-grown deciduous shade trees. M.S. Thesis Michigan State University 95 pp.
  • Type: Journal Articles Status: Published Year Published: 2020 Citation: Cregg, B., & Ellison-Smith, D. (2020). Application of Paclobutrazol to Mitigate Environmental Stress of Urban Street Trees. Forests, 11(3), 355.


Progress 10/01/18 to 09/30/19

Outputs
Target Audience:The target audience of this research is professional landscapers, arborists, and urban foresters. Results of the project of relevant to homeowners and amateur horticulturists as well. Changes/Problems: Nothing Reported What opportunities for training and professional development has the project provided?This project provides the basis for a M.S. thesis for one graduate student, Riley Rouse. Ms. Rouse completed training to become a certified pesticide applicator in Michigan. She has also received training on use of plant physiology instrumentation (Li-Cor portable photosynthesis system, pressure chamber, SPAD chlorophyll meter, and TDR soil moisture measurements). She has also had training in data analysis and presentation. Two undergraduate students on the project have also received training with Li-Cor portable photosynthesis system, pressure chamber, SPAD chlorophyll meter, and TDR soil moisture measurements. How have the results been disseminated to communities of interest?Results of the proejct have been disseminated at regional and international conferences: Rouse, R. 2019. Improving root systems of container-grown trees through pre-plant root modification: shaving and bare-rooting. Arboriculture Society of Michigan ArborCon. February 13, 2019. Rouse, R. 2019. Improving root systems of container-grown trees through pre-plant root modification: shaving and bare-rooting. International Society of Arboriculture Annual Conference. August 14, 2019. What do you plan to do during the next reporting period to accomplish the goals?Work remaining: We are currently continuing the destructive harvest and root evaluation. We collected trunk disks and two-year-old shoots from each tree during the destructive harvest. The trunk disks will be separated into 2018 and 2019 annual rings. The annual ring samples and the shoot samples will be analyzed for carbon-13 composition at the Center for Stable Isotope Biogeochemistry at the University of California, Berkeley. Analysis of carbon-13 in plant tissue provides an integrated measure of plant moisture stress. This analysis will provide additional insights on theimpacts of the root treatments on tree moisture stress. Results and conclusions from the project will be written as a peer-reviewed publication (target journal: Urban Forestry and Urban Greening) as part of the Master's thesis for Riley Rouse, graduate research assistant on the project. We will also develop a summary article for professionals for the Michigan Nursery and Landscape Association's Michigan Landscape magazine.

Impacts
What was accomplished under these goals? We planted 96 shade trees at the Michigan State University Horticulture Teaching and Research Center (HTRC) in May 2018. The trees had been grown for two years in #25 (100 L) containers at the MSU Pot-in-Pot research nursery. The three cultivars were October Glory red maple, columnar tulip poplar, and Bloodgood London Planetree. During the container production phase, the trees were grown according to standard nursery practices in a substrate mix of pine bark and peat moss (85:15, v:v), irrigated daily, and fertilized with controlled release fertilizer (Osmocote Plus 5-6 month release 15-9-12) @ 60 g of nitrogen per tree each year. For the field planting in spring 2018, planting holes were augured using a 36" auger mounted on a skid-steer tractor. Twelve trees of each cultivar were assigned at random to one of four treatments: - Control - plastic container removed and trees planted without any root modification - Shave - outer 1" of roots removed on all sides and bottom of root-ball using a pruning saw - Bare-root wash - Root-ball soaked in large tubs and then all substrate remove with a stream of water from a garden hose. - Bare-root air-spade - All container substrate removed from root-ball using a pneumatic air-spade The study was installed in a complete block design with eight blocks (3 cultivars x 4 treatments x 8 blocks = 96 trees total). Planting depth was adjusted for all treatments so that the root flare of each tree was visible after planting. Holes were back-filled using unamended backfill. All trees were mulched with 3" of pine wood chips and thoroughly watered immediately after planting. Trees were watered periodically whenever less than 1" of rain was recorded at the MSU Hort farm Enviro-Weather site and no rainfall was predicted in the immediate forecast. Evaluation We assessed height and caliper at the beginning and end of each growing season. Soil moisture was assessed every two weeks during the first two growing seasons using a portable TDR soil moisture system (Trase II, Soil Moisture Equipment Inc., Santa Barbara, CA). Soil moisture was measured at 0-6" depth in the back-fill soil (approx. 12" from base of the tree) in a subsample of four blocks (even blocks only). We assessed predawn and mid-day leaf water potential every 2 to 3 weeks during the 2018 and 2019 growing seasons using a portable pressure chamber (Plant Moisture Stress, Inc., Corvallis, OR). Photosynthetic gas exchange was measured using a portable photosynthesis system (LI-6400XT, Li-Cor, Inc., Lincoln, NE). Water potential and gas exchange we monitored on a subset of four of the eight blocks. Initial results and current status: The response of trees to pre-plant root manipulation was species dependent. Bare-rooting, either by root washing or air-spading, resulted in significant mortality of tulip poplar trees. Ten out of 16 (62.5%) tulip poplar trees that were bare-rooted before planting died within the first growing season after planting. Mortality was especially high (87.5%) for tulip poplar trees that were bare-rooted with an air-spade. For the red maple trees, one tree died in each of three treatments; control, bareroot wash, and bareroot air-spade. There was no mortality among the planetrees in any treatment. In September 2019 (two growing seasons after field-planting) we conducted a destructive harvest on a subset of four reps of trees. The above-ground portion of each tree was divided into leaves, branches, and trunk, and all portions were dried and weighed. Root systems were excavated with a tree spade. All soil was removed from the root systems using an air-spadeand root systems were evaluated to determine the percent of the root system with circling roots and the amount of roots extending beyond the original rootball.

Publications

  • Type: Journal Articles Status: Published Year Published: 2019 Citation: Vandegrift, D. A., Rowe, D. B., Cregg, B. M., & Liang, D. (2019). Effect of substrate depth on plant community development on a Michigan green roof. Ecological Engineering, 138, 264-273.


Progress 10/01/17 to 09/30/18

Outputs
Target Audience:The primary intended audiences for the results generated by this research are nursery managers, landscape contractors, arborists, and urban foresters. The results will also be applicable to homeowners and non-profit groups that plant street trees or landscape trees. Changes/Problems: Nothing Reported What opportunities for training and professional development has the project provided?This project has provided training opportunities for two undergraduate students, two graduate students, and two technicians. The lead graduate student (Riley Rouse, Horticulture) has received training on measuring leaf water potential using a pressure chamber, soil moisture measurements with TDR, photosynthetic gas exchange and using a SPAD chlorophyll meter. She has also received training on field plot installation and experimental design. Undergraduate students have also participated in theuse of the pressure chamber, soil moisture measurements and leaf area measurements. All personnel on the project have gained experience in using an air-spade for root excavation. How have the results been disseminated to communities of interest?Results of the project have been disseminated through presentations at professional meetings, e.g., Michigan Nursery and Landscape Association and Arboriculture Society of Michigan. Progress on the project has also been discussed on the Garden Professors' blog and Garden Professors Facebook page. What do you plan to do during the next reporting period to accomplish the goals?Activities for the next reporting period will focus on three experiments which are at various stages of completion. Effects of root-ball shaving and plant growth regulation of establishment of container-grown shade trees. We recently completed a destructive harvest of trees from this trial to determine biomass allocation to leaves, shoots and roots. Once dry weights are determined for the various components, data collection will be complete. In the next period we will analyze the data and prepare a manuscript for HortScience or Arboriculture and Urban Forestry. ?Effects of root-shaving and bare-rooting on establishment of container-grown shade trees. We will continue data collection (survival, shoot and caliper growth, leaf water potential, photosynthetic gas exchange, etc.) through the 2019 growing season. In fall 2019 we will conduct a destructive harvest on a subset of trees to evaluate new root growth and root system quality. Species variation in response to pre-plant root manipulation. We will initiate a new experiment in spring 2019. We will receive 160 bare-root tree liners from a commercial nursery (J. Frank Schmidt and Sons, Co., Boring, OR) in April. 2019. We will include trees from four species in the trial; one of which has been resilient to pre-plant root treatments in our earlier trials ('Bloodgood' London planetree) and three species that are reported to be sensitive to root disruption before planting [bur oak (Quercus macrocarpa), tupelo (Nyssa sylvatica), and baldcypress (Taxodium distichum)]. We will grow the trees for two years under standard nursery culture in our pot-in-pot nursery at the MSU HTRC and use them for a field planting experiment to examine species variation in response to pre-plant root manipulation.

Impacts
What was accomplished under these goals? We reported on two experiments to evaluate the impact of cultural treatments on growth and establishment of container-grown London planetrees (Platanus × acerifolia 'Bloodgood'). In Experiment 1, fertilization at planting increased SPAD chlorophyll content on two of four measurement dates but did not affect cumulative height or caliper growth after two years. After two growing seasons, root-ball treatments (shaving or teasing) increased root growth outside the original root-ball compared to control trees. Both root-ball treatments also reduced circling roots. In Experiment 2, mulching at planting increased soil moisture and cumulative tree height and diameter growth. Shaving increased new root growth and both root-ball treatments improved root architecture and reduced circling roots. Overall, the study demonstrates that root-ball manipulations can stimulate new root growth and reduce circling roots. Mulch is a valuable aid to conserve soil moisture and increase tree growth. Fertilization at planting provided little benefit in this experiment, which may have been related to a high level of soil fertility at the site or nutrient loading of the trees from nursery culture prior to transplanting (Cregg and Ellison, 2018). Members of my lab completed data collection on a trial to determine the impact of root-ball shaving and application of paclobutrazol (PBZ) at planting on survival and growth of container-grown honey locust trees (Gleditsia triacanthos). Trees had been grown in #25 (100L) containers for two years and were planted in a field at the MSU Horticulture Teaching and Research Center (HTRC) in spring 2016. Trees were assigned at random to one of six combinations of root treatment x PBZ treatment; with or without root-shaving x 0, 75, or 150 ml of PBZ applied as a root drench at planting. Each treatment combination was replicated five times (30 trees total), and trees were planted in a randomized complete block design. Data collection included survival, shoot and caliper growth, pre-dawn and midday water potential, photosynthetic gas exchange, and SPAD chlorophyll index. In fall 2018, we destructively harvested 18 trees (three replications) to determine leaf, stem, trunk, and root biomass. In spring 2018 we initiated an experiment to compare the effects of root-ball shaving and bare-rooting container-grown trees at planting (spring plant). The study was installed as a 4 x 3 factorial of root-ball treatment (control, root shaving, bare-root/wash, or bare-root/air-spade) and cultivar [October glory red maple (Acer rubrum 'October glory', Bloodgood London planetree, or columnar tulip tree (Liriodendron tulipifera 'Fastigiatum')]. We removed all container substrate on trees in the bare-root treatment and corrected any obvious root defects (e.g., circling or stem girdling roots). Substrate was removed either by soaking and washing with water from a spray nozzle (bare-root/wash) or by soaking and removing substrate with a high velocity stream of air from an air-spade (bare-root/air-spade). All cultivar x root treatment combinations were replicated eight times and planted in a randomized complete block design in a field at the MSU HTRC. A second experiment (summer plant) was installed in July 2018. This experiment was similar to the spring plant experiment except that we did not include the bare-root/air-spade treatment, and treatments were replicated three times. Data collection for both trial included monitoring tree survival, shoot and caliper growth, pre-dawn and midday water potential, photosynthetic gas exchange, and SPAD chlorophyll index.

Publications

  • Type: Journal Articles Status: Published Year Published: 2018 Citation: Cregg, B. & Ellison, D. (2018). Growth and establishment of container-grown London planetrees in response to mulch, root-ball treatment and fertilization. Urban Forestry & Urban Greening, 35: 139147.


Progress 10/01/16 to 09/30/17

Outputs
Target Audience:Nursery managers, landscape professionals, arborists Changes/Problems: Nothing Reported What opportunities for training and professional development has the project provided?Two undergraduate research assistants collected most of the data during the season, providing them with hands-on training using TDR moisture system, SPAD chlorophyll meter, pressure chamber, and chlorophyll fluorescence measurements. Assistants also participated in plot and plant maintenance, weed control, irrigation management, and summarizing data. How have the results been disseminated to communities of interest?Results of this project have been disseminated at several professional meetings including Michigan Nursery Landscape Association Great Lakes Trade Expo, Minnesota Shade Tree Conference, and Arboriculture Society of Michigan. What do you plan to do during the next reporting period to accomplish the goals?We will destructively harvest a sub-sample of honeylocust trees from trial 1. We will use an excavator or tree spade to harvest the entire root system of sample trees. Total root biomass will be quantified and we will estimate the amount of new root egress into backfill soil from the original rootball. We will plant trees from study 2 into field plots at the HTRC in spring 2018. Trees will be subjected to one of three root treatments at planting including: 1) Control (no root-ball manipulation), 2) Shave (outer 1-2" of root-ball removed with a pruning saw to eliminate outer, circling roots) or 3) Root-washing (elimination of container substrate and correction of any circling roots or root defects). Periodic measurements will be collected during the growing season including tree survival, growth and shoot water potential.

Impacts
What was accomplished under these goals? We are currently conducting two trials. In trial 1, 60 honeylocust trees grown #25 gallon containers were planted in a field site at the Michigan State University Horticulture Teaching and Research Center (HTRC) in July 2016. Each tree was assigned at random to one of six treatments. The treatments were a 2 x 3 factorial of root-ball shaving (2 levels: shaved vs. control) and paclobutrazol application at planting (3 levels: 0, 150 ml or 300 ml per tree). Tree height and stem caliper were measured at the beginning and end of the 2017growing season. During the 2017 growing season we measured plant water potential, SPAD chlorophyll index and dark-adapted chlorophyll fluorescence. In the second trial we planted shade trees and conifers in containers of various sizes in spring 2016. All trees were planted in a standard substrate of pine bark and peat moss (80:20, v:v). Containers were top-dressed with fertilizers with varying proportions of phosphorous. In the shade tree block we planted bare-root liners of London planetree, tulip poplar and red maple in #25 gallon containers. The trees were fertilized with controlled release fertilizers (5-6 mo. release) containing 36, 17, or 10.5 g of P2O5 per tree. The rate of nitrogen was kept constant at 60 g N per tree. SPAD chlorophyll index was higher for tulip polar than for planetree but SPAD index decreased for both species with decreased P addition. In the conifer block we planted 400 2-0 white pine transplants in #3 containers in spring 2016. Eighty trees were assigned at random to one of 5 controlled release fertilizer treatments: -Control - no fertilizer -Osmocote blend 15-5-8 (5-6 mo release) -Osmocote blend 15-5-8 (8-9 mo release) -Nursery mix 23-4-8 (5-6 mo release) -Osmocote plus 15-8-12 (5-6 mo release) All fertilizers were top-dressed at a rate of 7 g of N per container In the spring of 2017, 40 trees from the 2016 Control group were assigned to receive one of two rates of a controlled release fertilizer (2-3 month). -Osmocote blend 12-6-8 (2-3 mo release) @ 7 g N per container (2017 only) -Osmocote blend 12-6-8 (2-3 mo release) @ 3.5 g N per container (2017 only) -All other treatments were re-applied as in 2016 Early in the 2017 growing season (May 31), mean chlorophyll fluorescence (Fv/Fm) of trees in the Control group was lower (P<0.001) than trees that had been fertilized in 2016. There was no difference in mean Fv/Fm among fertilizer products. By the middle of the 2017 growing season (August 1) mean Fv/Fm of trees that receive either the high or low rate of the 2-3 month product was significantly higher than the control trees and wasequal to trees that had been fertilizer for both season, indicating the rapid recover was of needle photosynthetic capacity was possible.

Publications

  • Type: Journal Articles Status: Published Year Published: 2016 Citation: Ellison, D. S., Schutzki, R., Nzokou, P., & Cregg, B. 2016. Root growth potential, water relations and carbohydrate status of ash alternative species following pre-plant storage. Urban Forestry & Urban Greening, 18, 59-64
  • Type: Conference Papers and Presentations Status: Submitted Year Published: 2017 Citation: Cregg, B. 2017. Impact of recycled water on plant growth. California Nursery Conference. July 27, 2017, Irvine, CA.
  • Type: Conference Papers and Presentations Status: Submitted Year Published: 2017 Citation: Cregg, B. 2017. Improving transplant success of container-grown trees. Minnesota Shade Tree Shortcourse. March 14-15, 2017, Arden Hills, MN.
  • Type: Conference Papers and Presentations Status: Submitted Year Published: 2017 Citation: Cregg, B. 2017. The case for mulch. Indiana Arborists Association. January 25, 2017, Indianapolis, IN.
  • Type: Conference Papers and Presentations Status: Submitted Year Published: 2017 Citation: Cregg, B. 2017. Nutrition management in container production. MNLA Great Lakes Trade EXPO, January 23, 2007, Lansing, MI.


Progress 12/01/15 to 09/30/16

Outputs
Target Audience:Nursery professionals, landscape contractors, tree service workers, homeowners. Changes/Problems: Nothing Reported What opportunities for training and professional development has the project provided?Results from this project formed the basis of an in-service training program for Michigan State University Extension field staff. (June 2, 2016). The project has also provided training for two undergradaute research assistants. How have the results been disseminated to communities of interest?The results of this research have been disseminated through refereed publications, professional publications, presentations at scientific conferecnes and professional meetings. What do you plan to do during the next reporting period to accomplish the goals?We will continue evaluations on several studies thatwere installed in 2016. We planted 60 container-grown honeylocust trees into a field plot at the Michigan State University Horticulture Teaching and Research Center. At planting half of the trees were assigned to a root-shaving treatment (outer 8 cm of roots removed) and half were not treated. Within each root treatment group trees were assigned to one of three plant growth regulator treatments (0, 75, or 150 ml paclobutrazol). In the next reporting period we will measure growth, plant water relations, photosynthetic gas exchange and SPAD chlorophyll index for all trees in the study. We are currently growing 180 shade trees of 3 species (60 each of Acer rubrum, Liriodendron tulipifera, and Platanus xacerifolia) in #25 containersat our research nursery. These trees will be used for transplant studies that will be installed in spring 2018. In collaboration with a cooperating nursery (Dutchman tree farms, Manton, MI) we are growing conifers (Pinus strobus and Picea abies) #5 and #7 containers. The trees have been treated with a range of concentrations of paclobutrazol (0 to 150 ml). We will measure shoot growth of the trees in 2017 in order to develop growth-response curves. The trees will be transplanted in spring 2018.

Impacts
What was accomplished under these goals? We conducted two trials to examine growth and physiological responses of bare-root treeliners to pre-plant storage and handling. In both trials, bare-root liners were given one of four treatmentsfor three weeks prior to planting: 1) control, 2) cold storage (4 deg. C), 3) sweating (warm, moist storage), or 4) heeled-in (outdoor storage). Subjecting trees to a warm, moist environment before planting (sweating)increased shoot dieback of Celtic occidentalis trees. Root growth potential was very low for Quercus spp. trees and varied by treatment for Celtis occidentalis trees. Taxodium distichum trees had a relatively highroot growth potential in all treatments. Stem water potential measured immediately before and after pre-plant treatments indicated that Quercus spp. trees and T. distichum trees were able to rehydrate duringsweating while water stress in C. occidentalis trees remained high (stem water potential <−2.0 MPa). The results suggest that poor transplanting success reported for Quercus spp. trees may be related to low root growth potential, whereas poor establishment of Celtis occidentalis trees is related to a combination offactors including desiccation, poor root regeneration and poor carbohydrate status. None of the pre-plant treatments reduced shoot dieback compared to control trees that were not stored prior to planting. We conducted two experiments to examine growth and physiological responses of London planetrees (Platanus × acerifolia 'Bloodgood') following transplanting. In the first experiment we planted 48 planetrees, from #25 containers, in 3×2 factorial combination of root-ball manipulation ('control' - no treatment; 'shaved' - outer 3 cm of roots removed; or 'teased' - outer circling roots teased apart) and fertilization (no fertilizer or 400 g of controlled release fertilizer (15-9-12:N-P2O5-K2O, 5-6 mo. release)). In the second experiment 48 planetrees from #25 containers were planted in a 3×2 factorial of root-ball manipulation and mulch (no mulch or 8 cm of ground pine park mulch). Fertilization did not increase height or caliper growth after two years (p>0.05) but increased (p<0.05) leaf SPAD chlorophyll index. Both root-ball treatments increased new root growth relative to the control. Shaving the root-ball increased new root growth by 67% compared to the control trees; whereas teasing apart the root-ball increased new root growth by 49% relative to control. Mulching consistently increased soil moisture at 0-15 cm and 0-45 cm depth and increased tree caliper and height growth. The results indicate that root-ball manipulation at planting can enhance new root growth. Mulching greatly improved soil moisture availability and growth after transplanting, whereas fertilization had only a modest impact on post-transplanting tree performance.

Publications

  • Type: Journal Articles Status: Published Year Published: 2016 Citation: Ellison, D. S., Schutzki, R., Nzokou, P., & Cregg, B. (2016). Root growth potential, water relations and carbohydrate status of ash alternative species following pre-plant storage. Urban Forestry & Urban Greening, 18, 59-64.
  • Type: Conference Papers and Presentations Status: Published Year Published: 2016 Citation: Cregg, B. & O'Connor, A. (2016). Improving transplant success in container trees. International Society of Arboriculture Annual Meeting. Ft. Worth, TX. Aug. 13-17, 2016.
  • Type: Conference Papers and Presentations Status: Published Year Published: 2016 Citation: Cregg, B. & Ellison, D. (2016). Mulch and root-ball manipulation affect establishment of container-grown London planetrees. American Society for Horticultural Science Annual Meeting. Atlanta, GA. Aug. 8-11, 2016.
  • Type: Conference Papers and Presentations Status: Published Year Published: 2016 Citation: Cregg, B. & Crain. B. (2016). Soil-applied paclobutrazol controls shoot growth of field- and container-grown conifers. American Society for Horticultural Science Annual Meeting. Atlanta, GA. Aug. 8-11, 2016.
  • Type: Conference Papers and Presentations Status: Published Year Published: 2016 Citation: Cregg, B. (2016). What can tree growth regulators do for you? Arboriculture Society of Michigan Annual Meeting. Lansing, MI. Feb. 8-10, 2016.
  • Type: Conference Papers and Presentations Status: Published Year Published: 2016 Citation: Cregg, B. (2016) The case for mulch. Michigan Nursery and Landscape Association EXPO. Lansing, MI. Jan. 25-27, 2016.
  • Type: Other Status: Published Year Published: 2016 Citation: Cregg, B. 2016. Dealing with drought. The Michigan Landscape 58(4)34-37.
  • Type: Other Status: Published Year Published: 2016 Citation: Ellison, D. & Cregg, B. (2016) Improving transplant success of container-grown trees. Michigan State University Extension In-service Training. East Lansing, MI. June 22, 2016.