(125) Response of Six Begonia Species to Different Substrate pH

Abstract

Substrate pH of soilless media directly affects nutrient availability. Limited information about the effect of substrate pH on growth of begonia species (not cultivated hybrids) was found in the literature. The objective of this study was to evaluate the effect of substrate pH on the growth and quality of six begonia species grown from June to Aug. 2004. The targeted pH ranges (<4.5, 4.5∼5.0, 5.0∼5.5, 5.5∼6.0, 6.0∼6.5, 6.5∼7.0, and over 7.0) of the peat-based substrates were obtained by adding seven different amounts of dolomitic hydrated lime: 0, 1.0, 1.3, 1.6, 2.0, 2.4, and 2.6 kg·m3. Begonia albopicta, B. cucullata var. cucullata, B. echinosepala var. elongatifolia, B. holtonis, B. fuchsioides (red), and B. fuchsioides (pink), were propagated by stem cuttings, and then transplanted into plastic containers. This experiment was a factorial experiment arranged in a randomized complete-block design. The pH was monitored weekly using the pour-through method and adjusted accordingly by adding flowable lime or a mild sulfuric acid solution. The pH values were averaged for each treatment of each species. There were significant differences between species in the inflorescence number and SPAD readings, but no interaction between species and substrate pH was found. Stem length, leaf area, and dry weight of each plant were significantly affected by species and substrate pH. B. albopicta performed best at substrate pH of 5.6 and 6.0, showing no symptoms of phytotoxicity. B. cucullata, above substrate pH 6.0, and B. holtonis at pH 5.0 and 5.6 had the highest vegetative growth and plant quality. Plant mortality was observed for B. cucullata and B. fuchsioides (red) at pH below 4.4 and 5.3, respectively.