Effect of Different Commercial Substrates on Growth of Petunia Transplants

Abstract

The objective of this study was to evaluate the growth and flowering of petunia (Petunia ×hybrida) transplants in response to seven commercial substrates with two water sources (fertigation and clear water irrigation). Seven commercial substrates used were Sunshine #1 Natural & Organic (SS), Metro-Mix 360 (MM), AgriTech (AT), Cornell Peat-Lite Mix B (CB), Jeff’s Organic (JO), LM-18, and LM-111. The experiment was a completely randomized 2 × 7 factorial design with six single-pot replications per treatment. With fertigation, substrate electrical conductivity (EC) decreased over time to 38 days after transplanting (DAT), and then did not further change. The AT substrate EC value was greater than others during the first 38 DAT. With clear water irrigation, substrate EC decreased over time to 31 DAT, and then did not further change. The AT substrate EC value was greater than other substrates during the entire petunia growth period. With fertigation, all substrate pH values were between 6.5 and 7.5 except AT and CB. The AT substrate had the greatest pH ranging from 7.5 to 8.0 during the petunia growth period. The CB substrate exhibited the lowest pH, which was between 5.8 and 6.3. Clear water irrigation had greater substrate pH values than fertigation. There was a substrate and water interaction for calcium (Ca), potassium (K), ammonium-nitrogen (NH4+-N), nitrate-nitrogen (NO3−-N), and sodium (Na) concentrations in substrate leachate. At 52 DAT, the shoot dry weight (DW), root index (RI), and flower number of petunia grown in AT substrate were greatest among all the substrates, but chlorophyll index (SPAD) was the lowest under either the fertigation or clear water irrigation treatments. The DW and RI of petunia grown in AT substrate were greater when fertigation was used than clear water irrigation, but the water source had no effect on flower number. For SS, MM, CB, JO, LM-18, and LM-111 substrates, fertigation increased petunia DW, RI, and flower number as compared with clear water irrigation, but not SPAD readings.