Evaluating red pine tree substrates for phytotoxicity and growth effects on seedlings and bedding plants

Authors: OWEN, W - Michigan State University; Altland, James

Submitted to: Acta Horticulturae
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/1/2019
Publication Date: 8/1/2021
Citation: Owen, W.G., Altland, J.E. 2021. Evaluating red pine tree substrates for phytotoxicity and growth effects on seedlings and bedding plants. Acta Horticulturae. 1305:31-38. https://doi.org/10.17660/ActaHortic.2021.1305.5.
DOI: https://doi.org/10.17660/ActaHortic.2021.1305.5

Interpretive Summary: Nursery growers tend to use the bark of softwood tree species forested or harvested from their region of the country. Loblolly pine (Pinus taeda L.), a species prevalent in the southern and southeastern U.S., has been used by industry and studied for decades by academia. However, little attention has been given to tree species that are more prevalent in the mid-western and northeastern U.S. and eastern Canada such as red pine (P. resinosa). To date, no such investigation using red pine as the main substrate constituent or amended to peat-based substrates for greenhouse bedding plant production exists. Therefore, our objectives were to evaluate red pine tree (RPT) substrates for phytotoxicity by conducting a seedling bioassay and to determine effects on annual bedding and vegetable plant growth. Substrates amended with 60 or 80% RPT resulted in similar or slightly reduced plant growth to those amended with 80% peat moss (PM). Reduced plant growth in these substrates was likely the result of the substrate pH, which was determined to be high (6.2-6.5) for most greenhouse crops. Growers may formulate or amend greenhouse substrates to contain 60% RPT in combination of PM and perlite (PL), but must be aware of potential changes to substrate pH.

Technical Abstract: Red pine (Pinus resinosa) has potential to be a greenhouse substrate component for growers in the mid-western and northeastern United States and eastern Canada. However, to date, no literature exists regarding the use of red pine as a greenhouse substrate component. Therefore, our objectives were to evaluate and determine the effects of red pine tree (RPT) substrates on seedling and bedding plant growth. Processed and screened RPT (avg. particle dimension: 0.8× 0.3 × 0.2 cm) was received from a commercial mulch manufacturer and amended with peat moss (PM) and/or perlite (PL) to formulate (by vol.) 0:4:1, 4:0:1, 3:1:1, and 1:0:0 RPT:PM:PL substrates. Germination bioassays were used to determine potential adverse and phytotoxic effects in RPT-amended substrates. Five seeds of Chinese cabbage (Brassica rapa var. pekinensis), cucumber (Cucumis sativus), French marigold (Tagetes patula), radish (Raphanus sativus), and tomato (Solanum lycopersicum) were sown 1-cm deep in five containers of each substrate. Seedling germination count, phytotoxicity ratings, and seedling dry mass were similar among all substrates, indicating no detrimental effects. A plant growth trial with calibrachoa (Calibrachoa hybrida), French marigold (T. patula), geranium (Pelargonium × hortorum), pepper (Capsicum annuum), petunia (Petunia × hybrida), tomato (S. lycopersicum), and vinca (Catharanthus roseus) was conducted. Substrate pH and electrical conductivity (EC) were similar among all substrates, however plant dry mass were smaller for most plants grown in substrates formulated with =80% RPT. For example, dry mass of calibrachoa, geranium, petunia, and tomato were 26, 26, 56, and 14% less, respectively, when plants were grown in the 4:0:1 than the 0:4:1 RPT:PM:PL substrate. Results from the plant growth trial indicate less plant growth and thus lower plant quality when a greenhouse substrate is formulated with =80% RPT.