Microbial Biostimulants Promote the Growth of Greenhouse Pansies at Low Fertilizer Rates But Not under Optimal Fertility

Beneficial microorganisms offer greenhouse growers a strategy to enhance plant nutrient uptake and reduce fertilizer inputs during floriculture crop production. This study evaluated whether high-quality plants could be produced with reduced fertilizer rates when treated with biostimulants containing beneficial bacteria or fungi (a.k.a. microbial biostimulants). The efficacy of two commercial biostimulants, one with mycorrhizae as the active ingredient and a second with Bacillus subtilis as the active ingredient, was evaluated on the production of Viola × wittrockiana ‘Delta Pure Rose’ (pansy) under 0, 0.25, 0.5, 0.75, or 1.0× fertilizer rates from water-soluble fertilizer, where 1.0× equaled 150 mg·L –1 nitrogen. Plant performance was assessed by flower numbers, shoot and root dry weights, and visual observations. With no fertilizer, both biostimulants improved flower numbers and plant biomass compared with untreated controls. At 0.5× fertilizer, the biostimulant-treated plants were equal in quality to untreated plants receiving full-strength fertilizer. These results suggest that microbial biostimulants can support high-quality floriculture crop production under reduced fertility conditions.