Use of Fiber Containers in Pot-in-Pot System for a Two-year Nursery Production of Birch

Birch (Betula nigra) bare root liners were planted into two types of fiber containers (seven gallon, Kord^® Fiber Grow, Western Pulp) and one plastic container (seven gallon, GL 2800, Nursery Supplies^® Inc), which were used as the production pots in a pot-in-pot production system (PIP). Production pots were inserted into a GL 6900 (15 gallon) socket pot. The study was initiated in mid-June 2011 at four locations, KY, MI, MS and TX, and lasted through October 2012. Plant height, widths (Plant growth index (PGI) = (height+ width + perpendicular width)/3), and plant caliper (20 cm above ground) were measured at all locations at monthly intervals. Substrate moisture was determined with a calibrated theta probe (ML2, Dynamax Inc.) in KY with daily irrigation applied to replace 100% of daily water use (DWU). At the end of each growing season, a visual and tactile evaluation of the fiber containers was conducted to assess container strength. Birch plants were destructively harvested in October 2012. Above ground dry weight, root dry weight, and total dry weight were determined. There was no significant difference in plant height, plant dry weight, plant caliper or PGI among plants grown in different container types in MS, KY, or TX. Data from KY showed that there was no significant difference of DWU of plants grown in all three container types. At the end of the 2011 growing season fiber containers were still intact but by the end of the experiment roots had penetrated the bottom of the containers. In MS, bottom of fiber containers were severely penetrated by birch roots by October 2012 due to vigorous root growth; whereas, in KY, plant growth was less vigorous with only a few roots found penetrating the bottom of the pots.