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

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.