The Effects of Tree Harvest Season and Storage Method on Plant Growth in a Pine Tree Substrate

Recent interest in pine tree substrates (PTS) in horticultural crop production has generated many possibilities as well as unanswered questions about its use. While much research has been conducted on plant growth in PTS, wood manufacturing, wood toxicity, etc., there remains limited information available on plant growth during production as it relates to: 1) pine tree harvest date; 2) changes to manufactured PTS during storage; or 3) changes to harvested pine tree logs (before being manufactured into PTS) during storage. Therefore, this research was conducted to determine the influence of harvest season and the effects of storage time of PTS following manufacturing and the effect of log storage following harvest on plant growth in PTS.  In April 2007 and every three months through Oct. 2008, coarse pine chips produced from freshly harvested 15-year old loblolly pine trees (Pinus taeda L.) were ground in a hammer mill fitted with a 2.38-mm screen. At each harvest date some of the manufactured PTS was stored in 1.5 m^-3 perforated plastic bags and some of the whole unchipped logs were stored outdoors with bark intact.  Also at each harvest date, some of the PTS from a freshly harvested tree and a peat lite substrate (80:20 peat:perlite; PL) was used to grow ‘Inca Gold’ marigold (Tagetes erecta) in 1-L plastic pots to determine if harvest date affected growth in comparison to plant growth in PL.  In July 2008 and Oct. 2008, PTS manufactured from freshly harvested pine trees and PTS that had been stored since each of the four previous harvest dates (July 2007, Oct. 2007, Jan. 2008, April 2008; 12, 9, 6, 3 months, respectively) and PTS prepared by grinding logs that had been stored since the four previous harvest dates were filled in to individual containers.  Seedling marigolds were grown in these substrates to determine the effect of tree harvest season and storage time on plant growth. Results showed that PTS quality in terms of affecting plant growth is not affected by the season of year in which trees are harvested.  Storage of manufactured PTS in bags and stored whole pine logs (before grinding) resulted in a drop in pH (6.1 to 3.5) after 12 months. A reduction in plant growth was observed in the 12 mo aged PTS when lime was not incorporated to increase substrate pH compared to PTS manufactured from freshly harvested trees which had an acceptable pH for marigolds.