Economic and Cultural Effects of Reducing Substrate Moisture Content during Greenhouse Production of Bedding Plants

Retail environments are rarely optimum for ornamental plants, and wilting caused by water stress is a main cause of post production shrinkage. The objective of this research was to determine if withholding water during greenhouse production would increase plant tolerance to postharvest water stress. Our hypothesis was that withholding water during greenhouse production would increase plant tolerance to post-production water stress without a significant reduction in visual quality of the plant. If this hypothesis was correct, then the cost of production and the amount of water required would be reduced.

This experiment was conducted in a greenhouse, using two substrate moisture (SMC) levels: 20% and 40%, and 10 replications for each SMC treatment. Two plants species were tested: angelonia (Angelonia angustifolia ‘Angelface Blue’), and heliotrope (Heliotropium arborescens ‘Simply Scentsational’). During eight weeks of greenhouse production, plants were hand watered to container capacity after reaching the treatment moisture level and allowed to dry down again several times from plant establishment until plants were deemed marketable. Weekly data collection during production included plant growth index (GI); leaf greenness index (SPAD); substrate leachate electrical conductivity (EC) and pH; plant net photosynthetic rate (A); and midday water potential (ψ). At the stage when the plants were deemed to be marketable based on industry standards, plants went through a simulated shipping process in the dark for 48h followed by two weeks of simulated shelf life, during which plants were watered when wilting began to occur. Timing of all cultural and labor inputs during production and postproduction were recorded for partial budgeting economic analysis. At termination of production and shelf life, data collection included: total inflorescence number; plant and flower dry weight; root to shoot ratio; SPAD; water-use efficiency; and middle day water potential.

During production, angelonia grown at 40% SMC had higher GI and A than those grown at 20% SMC in week 7 and 8. Both angelonia and heliotrope grown at 40% SMC had higher SPAD readings than those at 20% SMC in week 5 and 6, conversely, in week 7 and 8, plants grown at 20% SMC had higher SPAD readings.