Quantifying the effects of fifteen floriculture species on substrate-pH

Floriculture species differ in their effect on substrate-pH and the resulting substrate micronutrient availability in container production. The objective was to quantify effects of floriculture plant species on substrate-pH. In a growth chamber factorial experiment, 15 floriculture species were grown in 70%:30% by volume peat:perlite substrate and fertilized with nutrient solutions containing 100 mg L^‑1 N at NH₄⁺-N:NO₃^--N nitrogen ratios of 0:100, 20:80, or 40:60. After 33 days, species and solution type effects on substrate-pH and estimated mEq of acid or base produced were evaluated. Final substrate-pH ranged from 4.83 for geranium (Pelargonium × hortorum Bailey L.H.) in 40:60 solution to 6.58 for lisianthus in 0:100 solution, compared to an initial substrate-pH of 5.84. This change in substrate-pH corresponded with a net mEq of acid or base produced g^‑1 tissue dry mass gain (NMEQ) ranging across solutions and species from 1.47 of base for lisianthus (Eustoma grandiflorum Salisb.) in the 0:100 solution to 2.10 of acid for coleus (Solenostemon scutellariodes L.) in the 40:60 solution. With the 0:100 solution, species that took up more anions than cations into plant tissue tended to have a more basic effect on substrate-pH, as would be expected to maintain electroneutrality. Data were used to estimate the percent NH₄⁺-N of total N in a nutrient solution that would be neutral (result in no substrate-pH change) for each species. This neutral percent NH₄⁺-N of total N ranged from approximately 0% for geranium to 35% for pentas (Pentas lanceolata Forssk.). Evaluating the tendency to raise or lower substrate-pH across a range of floriculture species could help predict NH₄⁺:NO₃^- ratios for a neutral pH effect and assist growers in managing substrate-pH for container production.