Fertilizer Selection as a pH Management Tool in Floriculture Production

Connie N Johnson, Paul A Fisher, Jinsheng Huang


The acid or base potential of fertilizer is an important factor to consider in pH management of floriculture crops. The potential of water-soluble fertilizer (WSF) to decrease or increase substrate-pH is expressed in calcium carbonate equivalents (CCE) of acidity or basicity per unit weight of fertilizer. The objective was to quantify the effect of 18 WSFs with varying CCE values and nitrogen ratios (% NH4-N, NO3-N, or urea-N) on substrate-pH response of Pelargonium×hortorumBailey ‘Ringo Deep Red’, Impatiens wallerianaHook ‘Super Elfin Bright Orange’, and Petunia × hybrida‘Ultra Red’ grown in 70% : 30% (v:v) peat : perlite substrate amended with dolomitic hydrated limestone. Six plants per 900 mL (54.92 cubic inch), 6-celled container, were top-irrigated with a total of 3.07 L (0.81 gal) over 4 weeks using one of 18 WSFs applied at 100 mg·L–1 (ppm) N without leaching. Fertilizer CCE explained 67% to 91% of the variation in substrate-pH observed. Nitrogen accounted for 66% to 89% of the variation in substrate-pH change, whereby NH4-N and urea-N had acidic reactions and NO3-N had a basic reaction. Acid or base reaction of fertilizer varied across species, with the most basic reactions in petunia, the most acidic in pelargonium, and with impatiens having intermediate pH-responses.


calcium carbonate, Pierre, peat, substrate-pH

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Proc. Fla. State Hort. Soc.     ISSN 0886-7283

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