Effects of Maintained Substrate Gravimetric Water Content from Transplant to Finished Stage on Impatiens x walleriana ‘Xtreme Red’

Growers differ on the ideal substrate moisture content for bedding plants immediately following transplanting. In this experiment, Fafard 3B was maintained at five gravimetric water content (GWC) levels to determine effects on Impatiens ^×walleriana shoot and root growth as well as depth of root growth within the substrate profile. Plugs were potted into 15 cm containers and irrigated initially to 64%, 68%, 72%, 76% or 80% GWC. Plants were irrigated by hand daily using a 60 mL syringe to bring it to its target GWC. The experimental design was a completely randomized block. Substrate pH and EC were collected three and six weeks after potting (WAP) while size indices were collected weekly. At six WAP, shoots were harvested, and containers were brought back to container capacity and placed in a freezer at -2 °C. After freezing, root balls were divided in half using a machete and rubber mallet. An increase in GWC resulted in an increase in size index, shoot dry weight, and root dry weight. There was a moderate increase in size index between 64% and 76% target GWC (9.6%) and a substantial increase between 76% and 80% target GWC (24.2%). Irrigation volume increased substantially between 64% and 76% target GWC (33%) and increased moderately between 76% and 80% target GWC (29%). Substrate maintained at 80% GWC resulted in the highest percentage of roots in the bottom half of the substrate profile. Results may differ in finer textured substrates that have less air space.