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Luke Case, Hannah Mathers and Elizabeth Grosskurth

Many Ohio growers import liners from the West Coast due to the increased growing season on the West Coast. Lengthening the season in Ohio may provide a way for Ohio growers to produce liners of their own. Retractable roof greenhouses (RRG) are one possible way to extend the growing season in Ohio. Research done previously at The Ohio State University suggests that retractable roof greenhouses do in fact lengthen the growing season, and tree liners can be produced using RRG. The objectives of this study were: 1) to determine the optimal growing environment from three different environments; and 2) to determine the optimal species for tree liner production in Ohio. In Oct. 2004, 180 liners each of Cladrastis kentuckea, Quercus rubra, Stewartia pseudocamellia, Syringa reticulata, and Tilia cordata were upshifted to 3-gallon pots. In Mar. 2005, 90 of each species were transferred to either a flat roof retractable house (FRRG), peak roof retractable house (PRRG), or polyhouse. Growth was measured in Mar. (initial), June, Aug., and Oct. 2005 by taking leaf area, shoot and root dry weights, height, and caliper. There were no differences across species and dates between the environments for any of the parameters measured. Tilia showed the greatest increase in growth from June to October in all the parameters measured except leaf area. Cladrastis showed the greatest increase in leaf area from June to October. There were species by date interactions. Quercus had the greatest root weight in October. Syringa and Quercus were not significantly different from each other and had the highest shoot weights and leaf areas in October. Tilia, Quercus, and Syringa had the highest calipers in October.

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Alison A. Stoven*, Hannah M. Mathers and Daniel K. Struve

A study was conducted to determine if similar quality shade tree liners could be produced using a retractable-roof greenhouse structure versus an outdoor environment. All plants were started in a heated greenhouse on campus in 250 XL-sized containers. The species included Eastern redbud, red oak (both grown from seed) and Autumn Blaze maple and Prairifire crabapple (both grown from rooted cuttings). On 15 Mar. 2003, half the plants remained in the heated greenhouse and the other half were moved to a Cravo retractable-roof structure and placed on heating mats set at 22 °C. In May, all of the plants (retractable and greenhouse) were upshifted into 3-gallon Spin-out® treated containers. Trees in each environment were fertilized with either Osmocote® (20 N, 2.2 P, 6.6 K), nine month release, applied broadcast at 45 g/pot, or with a 100 ppm-N water-soluable fertilizer (21 N, 3.1P, 5.9 K), applied at 0.1 g N/day. All trees received the same irrigation volume (1 L/day). All trees were grown according to nursery standards including bamboo staking, taping and regular pruning. Plants were arranged in a completely randomized design in each environment. The Cravo structure provided a more uniform environment with reduced air and soil temperature fluctuations versus the outdoor environment. Liners produced in the Cravo structure were taller, had greater caliper and root and shoot mass. Slow release fertilizer produced larger plants. Root dry weight for trees inside the Cravo environment increased nearly five times over the harvest dates of July to October with the maples having the largest root weight.

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Jennifer Nelkin and Ursula Schuch

Fresh weight production of basil (Ocimum basilicum`Genovese') growing in a retractable roof greenhouse (RRGH) or outdoors was evaluated under different shade environments, cultural production systems, and roof control strategies in a semi-arid climate. Cultural production systems included raised beds and towers consisting of six pots arranged vertically and stacked on edge. The growing substrate in both systems was perlite. The three shade environments included a RRGH with either a clear woven roof (35% shade) or a white woven roof (50% shade), or outdoors in full sun (0% shade). Within the RRGH, three strategies of roof control were tested based on air temperature thresholds, quantum thresholds, and globe thermometer temperature thresholds. After establishment, plants were grown for 4 weeks, each under the three roof control strategies in each environment and in both cultural systems. New shoots were harvested weekly and fresh weights were determined. Overall, fresh weight per plant was significantly affected by cultural production system, and basil grown in raised beds produced twice the biomass compared to plants grown in vertical towers. Productivity of basil grown in raised beds was not affected by the three shade environments, but plants in vertical towers produced about 20% more when grown in full sun or under 35% shade compared to under 50% shade. Within the RRGH, roof control strategy significantly affected basil fresh weight per plant. Roof control, based on either a quantum sensor or globe thermometer, increased production by 31% compared to air temperature control. Greater productivity was related to higher cumulative light exposure of plants. Quality of basil grown in the RRGH was superior to that grown in full sun.

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Hannah M. Mathers

Container nurseries are generally more productive than field nurseries because plants can be produced faster and at higher densities. Increasingly, nursery stock is being propagated, grown, and marketed in containers. The prime biological advantage of container stock over bareroot and field-grown balled and burlapped (B&B) stock is that the root system is packaged and protected from transplant or mechanical stress; however, temperature stress limits container production. Plants overwintered in containers suffer greater winter injury than those in the ground because the roots are surrounded by cold, circulating air rather than the insulating environment of the soil. There are several methods for providing protection from cold winter temperatures that are used in the nursery industry; however, all are labor intensive, expensive and vary in effectiveness. Container stock also suffers from elevated summer root zone temperatures. Cultivar differences in the degree of summer injury have been reported. With increasing human population pressures and decreasing availability of fresh water supplies, the need for more water-efficient nursery cultural practices becomes increasingly important. Water and nutrient use efficiency are predominant factors restricting nursery container production. Cultural factors that improve root function and reduce root injury and container heat load are considered key to improving these efficiencies. This paper examines temperature stress issues and the effects of different nursery cultural environments such as conventional overwintering systems, conventional gravel production surfaces, pot-in-pot production, and retractable roof greenhouses.

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Hannah M. Mathers, Elizabeth Grosskurth, Michele Bigger, Luke Case and Jenny Pope

Currently, the majority of tree liners used in the Ohio nursery industry are imported, mainly from the West Coast. The Ohio growing season is 156 days, whereas the Oregon season is 225 days. We are developing an Ohio liner production system, utilizing a retractable roof greenhouse (RRG) that extends the growing season. Liners grown in a RRG have shown greater caliper, height, and root and shoot dry weight than those grown outside of a RRG (Stoven, 2004). The objective of this research was to compare the growth of RRG-grown liners, outdoor-grown liners, and West Coast-grown liners when planted in the field. Four tree species [Quercus rubra, Malus `Prairifire', Acer ×freemannii `Jeffersred' (Autumn Blaze®), and Cercis canadensis] were started from either seed or rooted cuttings in early 2003. They were grown in a glass greenhouse and then moved to their respective environments in March (RRG) and May (outside). In Oct. 2003, the Ohio-grown liners were planted in the field at the Waterman Farm of The Ohio State University, Columbus. In Spring 2004, liners from the West Coast were purchased and planted in the same field setting. Caliper and height were measured in June and Sept. 2004. After one season in the field, trees grown from the RRG and outdoor environments resulted in greater height and caliper than the West Coast liners in Malus, Acer, and Cercis. Acer liners from Oregon had a greater increase in height from June to September than those grown outdoors or in the RRG. Quercus liners from the RRG and outdoor environments displayed greater caliper growth and growth in height than those from the West Coast. Across all species, liners grown from the RRG had the greatest increase in caliper growth.

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Ursula K. Schuch, Jack J. Kelly and Trent Teegerstrom

and water application. For the first experiment, plants ready for retail sales were obtained from local nurseries and on 4 Aug. 2005 were placed in a simulated retail environment in a retractable roof greenhouse at the University of Arizona in Tucson

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Neil Bell, Heather Stoven, James S. Owen Jr. and James E. Altland

grown in an unheated retractable roof greenhouse (Cravo, Brantford, ON) until planting in the field site for evaluation. Despite the difference in the collection time of royal grevillea (variegated), the long period of growth during Summer 2011 resulted

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M. Gabriela Buamscha, James E. Altland, Dan M. Sullivan, Donald A. Horneck and John P.G. McQueen

leach the container and reduce salt build-up. The experiment was conducted in a retractable roof greenhouse (Cravo Equipment, Brantford, ON, Canada) in Aurora, OR (lat. 45°14′N, long. 122°45′W). The greenhouse roof was opened throughout the day, but was

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James E. Altland, James S. Owen Jr. and Magdalena Z. Gabriel

exceptions. In Expt. 2, ‘Blue Prince’ holly were potted into the aluminum cores on 8 Mar. 2007 and grown until 25 Mar. 2008. All cores were located in a retractable-roof greenhouse in which the roof remained open throughout the spring and summer months, but

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James E. Altland and M. Gabriela Buamscha

for ≈6 months (Marr Bros. Co., Monmouth, OR). Eight No. 1 containers (2.8 L) were filled with each bark batch and maintained in a retractable roof greenhouse (Cravo Equip. Ltd., Brantford, Ontario, Canada) in Aurora, OR. Containers were overhead