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Evaluation of WholeTree as an Alternative Substrate Component in Production of Greenhouse Grown Annuals




Griffin, Whitney

Type of Degree





The physical properties and growth of greenhouse annuals in chipped pine log (CPL) and WholeTree (WT) alternative substrate components were evaluated. Both wood-fiber alternatives have been reported as suitable for the greenhouse production of annuals; however, the two had not yet been compared. CPL is composed of a pine log while WT is composed of all aboveground portions of a pine tree, including wood, bark, needles, and branches. Plants grown in WT and CPL perform similarly - while minor differences in physical properties were present, these had no apparent affect on plant growth as plant response data were generally similar. Interestingly, we did find differences between experiment 1 and experiment 2 – the plants in both substrates were larger in experiment 2, even though there were no treatment differences. This led to the hypothesis that aging a wood fiber substrate may be beneficial to plant growth, leading to the second experiment In a second experiment, physical properties and growth of greenhouse annuals in aged and fresh WholeTree substrate were evaluated. In both experiments aged material was aged a minimum of 90 days while fresh material was used no more than 2 days past processing. Plants grown in aged WT had higher growth indices, more blooms, greater dry weights, and greener leaves than those grown in fresh WT. In physical properties, aged WT had less air space and a greater container capacity than fresh WT. While the overwhelming differences in plant response may be attributed to physical properties, we felt that there may be some chemical present in the needles in fresh WT that had a phytotoxic effect on plant growth. The potential phytotoxicity of aged and fresh WT was evaluated in a third experiment. Lettuce seeds were germinated in increasing concentrations of aged or fresh pine needle leachate. There were no differences in germination percentage; however, radicle length was longer in seeds germinated in aged needle leachate compared to those germinated in fresh needle leachate. This indicates that the differences in aged and fresh WT may be attributed to a phytotoxic chemical response.