The 2011 ASHS Annual Conference

Currently caliper tree production in Ohio relies on tree whips grown in the Pacific Northwest, which impedes the Ohio nursery industry due to damaged nursery stock and limited selection.  One of the obstacles to growing tree liners in Ohio is the shorter growing season.  Use of retractable roof greenhouses has been shown to produce larger trees than outside production (Stoven, 2006).  Pots that air prune root systems, which are useful for improving root architecture through fewer girdling roots, have been shown to increase plant size as well (Maguire, 2007; Mathers, unpublished data).  Three different species, Quercus shumardii, Platanus occidentalis, and Gleditsia triacanthos were started from seed in February 2010 from germplasm collected in Columbus, OH.  Trees were planted into four different air pruning pots – a Jiffy® peat pot, a Rootmaker®, Root Accelerator® and Elle® paper pot or a control 3-gallon pot.  After one month, all plants in the root pruning pots were up-shifted into three gallon pots, which they grew in for the remainder of the growing season.  Plants were split between a retractable roof greenhouse environment and outside on a black geofabric.  After entering dormancy, plants were measured for caliper, height, shoot and root weights.  Q. shumardii average growth in height, dry root weight, and dry shoot weight, and caliper was higher in the Rootmaker® or planted directly into the 3-gallon pot.  G. triacanthos height was higher in any air pruning pot compared to the control 3-gallon pot, but dry shoot weight, dry root weight, and caliper were affected only by the Rootmaker ®.   G. triacanthos grown in the retractable roof greenhouse had an average caliper larger than trees grown outside.  Q. shumardii was larger in height, dry root weight, dry shoot weight, and caliper when grown in the retractable roof greenhouse than outside.  This data suggests that a combination of a retractable roof greenhouse and air pruning pots can speed the growth of specific tree species to the same rate as ones grown in the Pacific Northwest.