Evaluation of Sustainable Alternative Substrate Components for Container Plant Production

Abstract

Pine bark, peat, and perlite have served as the standard substrate components of container-grown plants for over 50 years. Due to a number of factors, including increased transportation costs, a shift to in-field harvesting of pine, and proposed federal programming, the future availability of pine bark is widely unknown. The future availability of peat for horticultural use is also unknown due to increased regulations and restrictions on the harvesting of peat. These restrictions, paralleled with constantly fluctuating fuel and shipping prices of peat from Canada, have caused growers to seek alternative greenhouse substrates with equivalent physical characteristics. Additionally, growers are becoming increasingly concerned about amending their container substrates with perlite. Up until now, perlite has simply been considered a general nuisance due to its dusty nature, but increasing concerns related to health issues have caused growers to seek alternative greenhouse substrate amendments with equivalent characteristics to perlite. The main objective of this work is to identify and evaluate possible substrate alternatives or amendments to pine bark, peat and perlite. First, clean chip residual (CCR) and WholeTree (WT) were evaluated in order to observe how far existing bark-based substrates could be amended without negative effects on the growth of woody ornamentals. This study was developed to evaluate substrate treatments comprised of PB with 25%, 50%, and 75% CCR or WT, as well as 100% substrates of each high wood fiber substrate. By 180 and 365 DAT, pH and electrical conductivity (EC) values for all treatments were similar to those of the 100% PB control. Growth data at 365 days after planting (DAT) showed that with all nursery crops tested, nursery producers could use 75% CCR or 75% WT in their standard PB substrate with limited impact on crop growth. While there were a few differences in pH and electrical conductivity between CCR and WT early in the study, treatments were not significantly different by study termination (365 days after planting). There were little to no differences in plant growth across all treatments for all species tested (azalea, lantana, spirea, osmanthus, ligustrum, and holly) at the study termination. Next, we evaluated three low-value forest trees (sweetgum, hickory, and redcedar) as possible amendments to standard greenhouse substrates. These studies evaluated three possible substrate alternatives for use in greenhouse products, including fresh sweetgum (SG), hickory (H), and eastern redcedar (RC), in addition to WholeTree (WT) substrate. Three greenhouse annual crops (petunia, impatiens, and vinca) were planted in varying ratios of these species mixed with peat. Plants grown with SG and H as amendments did not perform as well as a traditional peat:perlite mix with respect to flower number, growth indices, and plant dry weight. However, plants grown in RC tended to be equivalent to those grown in a traditional mix. Data showed that greenhouse producers could amend their standard greenhouse substrate with up to 50% eastern redcedar with little to no differences in plant growth.