Establishment of greenhouse-grown Tagetes patula and Petunia x hybrida in 'WholeTree' substrates

Rising transportation cost of peat moss from Canada or Europe is negatively affecting the profitability of many greenhouse operators. The industry has recognized a need to explore alternatives to peat for greenhouse substrates. The objective of this research was to evaluate processed whole pine (Pinus taeda) trees (WT) as an alternative growth substrate for greenhouse crops. Studies were conducted at the Southern Horticultural Laboratory (SHL) in Poplarville, MS, USA and Young's Plant Farm (YPF) in Auburn, AL, USA. Loblolly pine (Pinus taeda L.) was harvested from a 10 year old planted pine plantation in south Mississippi. The entire shoot portion of including needles was processed in several stages to pass a 0.48, 0.64, or 0.95 cm screen. The resulting three WT substrates were used alone or mixed with 20% or 50% (by volume) Canadian sphagnum peat moss (peat) and compared to an industry standard mix of 8:1:1 (by volume) peat:vermiculite:perlite (peat-lite). On 14 April 2006 (20 April 2006 for YPF) 15.2 cm containers were filled and four plugs (288 cell) of either marigold (Tagetes patula 'Little Hero Yellow') or petunia (Petunia xhybrida 'Dreams Pink') were planted into each container. At 34 days after potting (DAP) there were no differences in flower number for marigold. Petunias grown in peat-lite substrate had over twice the number of flowers than observed on plants grown in other substrates. Leaf chlorophyll content was similar for petunia and marigold among all substrates. Regardless of substrate treatment all marigolds were considered marketable at 34 DAP. At 28 DAP, petunias grown in any 100% WT or 4:1 WT:peat substrate were smaller than plants in any 4:1 WT:peat or the peat-lite substrate. At 28 DAP petunia grown in peat-lite substrate were also larger than those grown in any 4:1 WT:peat substrate however all plants were considered marketable. The results of this experiment indicate that whole tree substrates are a potential alternative to conventional greenhouse substrates especially when combined with peat moss.