Optimum Substrate Moisture Content Improves Quality of Impatiens and Coleus

Maintaining proper moisture content is essential to the success of a variety of crops because it affects the amount of water and fertilizer application, disease incidence, plant growth and production cost, and ultimately determines farm income. The purpose of this study was to determine the optimum moisture content to enhance productivity and quality of impatiens (Impatiens sodenii) and coleus (Solenostemon scutellarioides). Plants were potted into 15-cm pots containing Sunshine #1 medium mixed with fully expanded Soil Moist (SM) hydrophilic polymers at different mixing ratio, 0 % (100:0, v:v) as control, 20 % (80:20 v:v), 40 % (60:40 v:v), 60 % (40:60, v:v), or 80% (20:80, v:v).  Volumetric water content (VWC) was monitored by using a soil moisture detector (SPTDR100, USA) and maintained by fertigating plants when the VWC was below threshold. In impatiens, plant height and the number of branches and leaves were significantly higher at 20% mixing ratio during the 6 weeks of growing period. In coleus, lower mixing ratio significantly enhanced plant growth, but there was no big difference among 0%, 20% and 40%. However, leaf surface area was significantly increased at 20% in both plant species, resulting in a higher shoot dry weight. In addition, plants grown at 20% had greater root dry weight, and a higher root-to-shoot ratio regardless of plant species. Mixing ratio over 60%, however, negatively affected plant growth. Measurements of VWC showed that mixing ratio of 20% maintained higher VWC compared to that of control, resulting in less water consumption during the entire production period in both plant species. Our results confirm that proper substrate moisture contents can help enhance plant productivity and quality. Taken together, maintaining an optimum water content will help reduce water input and produce better quality crops.