Impact of Parboiled Rice Hull-amended Substrates on the Growth and Quality of Geranium

Utilizing alternative, low cost, and renewable substrates to create growing mixes is an important strategy for sustainable greenhouse and nursery production. Parboiled Rice Hulls (RH) are an agricultural byproduct from rice mills, and have been suggested as a viable substitute to peat moss. This study was conducted to assess the impacts of replacing non-renewable peat moss in standard growing medium with RH on the production and quality of geranium (Pelargonium × hortorum ‘Bullseye Scarlet’). Plants were transplanted into 6-inch plastic containers filled with a substrate composed of commercial potting mix (CPM, 70% peat moss), or amended mix either with ground rice hulls (GRH, 30% peat moss and 40% ground rice hull) or whole rice hulls (WRH, 30% peat moss and 40% whole rice hull). Plants were fertigated to maintain 30% leaching fraction. Plant growth and flowering parameters such as plant height, growth index, leaf number, leaf area index, and inflorescence number and size were assessed throughout the study. It was found that CPM increased leaf number, leaf area and biomass by 45% compared to RH. However, plants grown in GRH and WRH produced uniform, denser and shorter plants whereas plants grown in CPM produced non-uniform, more spreading and taller plants. Plants grown in RH were about 50% shorter and 25% more compact than those grown in CPM. Even though plant height was similar when grown in WRH and GRH, WRH-grown plants were around 10% more compact than those grown in GRH. Flowering characteristics such as flowering initiation, height of flower stem and average size of fully open inflorescence were similar between plants grown in RH-containing substrates and CPM. Based on the results, it is evident that RH could be used as a promising alternative to peat moss for growing geraniums.