OFA Bulletin Sept/Oct 2010 : Page 2

OFA Mission Statement To support and advance professional horticulture. OFA – an Association of Horticulture Professionals 2130 Stella Court Columbus, Ohio 43215-1033 USA 614-487-1117 Fax: 614-487-1216 ofa@ofa.org www.ofa.org OFA Bulletin September/October 2010 NUMBER 923 Editorial Staff Stephen A. Carver, Ph.D. Laura Kunkle Editor Contributors Bridget K. Behe Stephanie Burnett Raymond A. Cloyd Richard S. Cowles Michael Evans Katherine Garland Lynn P. Griffith Jr Brian Krug Jeff Kuehny Amanda Long Kyle Miller Debra Ringler Matt Taylor Ask the Doctor Brian Krug bkrug@ceunh.unh.edu Controlling Plant Height Without PGRs Question: I often need to control the height of my plants. I know that I can use PGRs, but due to the small size of my operation, I can’t justify buying them. How can I control the height of my plants without using PGRs? Answer: Choose the Appropriate Plant Material Controlling plant height begins long before your plants arrive in your greenhouse by selecting plant material that is best suited for your needs. Pay attention to the listed height and spread in the catalogs when you are placing orders. Scheduling Have a target market date for the crop and work backwards from that date, giving the appropriate time for flower development and vegetative growth after transplanting. Overestimating the time needed will result in overgrown crops and the need to take other measures to control plant height. The schedule is an important part of production, so once you make a plan stick to it! Too often, we make a plan during the off-season, and it falls apart once spring hits. Write down your schedule and use it. Published Bimonthly Copyright© OFA 2010. Permission is hereby given to reprint articles appearing in this OFA Bulletin provided the following reference statement appears with the reprinted article: “Reprinted from the OFA Bulletin, (phone: 614-487-1117) September/October 2010, Number 923.” No endorsement is intended for products mentioned in this OFA Bulletin, nor is criticism meant for products not mentioned. The authors and OFA assume no liability resulting from the use of practices printed in this OFA Bulletin. 2 Spacing Once your plants are transplanted and growing in the greenhouse be sure to give your crop adequate spacing. Space is always at a premium in the spring, but keeping your crop pot tight too long will result in tall, leggy plants. The plants in Figure 1 are an all too common sight in the spring; the plants look good on the bench but customers are disappointed when they pick up an individual plant. Light Just as space is at a premium in the spring, so too is light, except for maybe in the South. Take the off-season to clean the glazing on your greenhouse. Algae and dirt buildup can substantially reduce the light getting to your crop. Don’t create a low-light situation in your greenhouse by over-utilizing the “free” space above the benches for hanging baskets (Figure 2). Using this space comes at the expense of the plants on the benches; hanging baskets intercept light coming into the greenhouse before it gets to the benches and shades the crops below. Of course, you are going to grow hanging baskets and you are going to use the space above the benches; however, use the space within reason. Temperature Sometimes we can lower the growing temperature in which we produce our crops. The petunias shown in Figure 3 were potted on the same day and grown in an identical fashion with the exception of night temperature. The plant on the left was grown at a night temperature of 55°F whereas the plant on the right was grown at a night temperature of 65°F. The plant grown at a night temperature of 55°F is considerably more compact. Using a negative DIF (warmer night temperature than day temperature) is also effective to control plant height with some crops. Utilizing temperature to control plant height can be a difficult task. We find our greenhouses full of dozens of different crops at the same time during the bedding plant season; not all plants respond similarly, and separating crops is not always an option. O F A B u l l e t i n

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