S06 - Session O6 - Evaluating alternative growing substrates to peat for ornamental horticulture.

Authors: Olivia Haines *, Ian Dodd, Richard Collins, Sarah Fairhurst

While peat has traditionally been used as an ideal growing medium for horticultural plant production, draining and destruction of peat bogs for use in growing media depletes a huge carbon sink. The horticultural industry urgently needs alternatives to peat based growing media, not only to exercise corporate social responsibility but increasingly to adhere to government guidance and/or legislation. While many horticultural industries have opted to use coir, this practice is questionable in terms of carbon balance since it must be transported from tropical regions to the UK and there are also concerns over the ethics of harvesting such products and periodic supply chain issues. In the UK, wood-based growing media has potential to be an effective replacement for peat, but whether its use can result in similar ornamental plant quality under typical nursery watering and fertilisation practices is uncertain. The high porosity of these media, while ideal for drainage, may limit root-soil contact necessary for plant water and nutrient uptake. Adding surfactants to these growing media may improve the distribution of soil moisture within them, but their effects on plant physiological responses to water deficit are relatively unknown. To evaluate the viability of alternative growing media, factorial experiments were set up with different ornamental species (e.g. petunia and dianthus), media (with and without surfactants) and irrigation treatments (well-watered versus deficit irrigation). Above-ground physiological measurements (leaf chlorophyll content, leaf area, and plant water relations including stomatal conductance and leaf water potential) and below-ground measurements (root architecture and rhizosheath development = medium adhering to the root system) were made throughout the growing cycle and at harvest respectively. Visual quality assessments were made according to industry standards. Life cycle analyses of the various media were performed to complement more traditional assessments of horticultural performance, to produce relevant industry guidance on product sustainability.