Fertilizer Rate, Soil Type, and Beneficial Microorganism Application Influenced Poinsettia Growth and Development

Beneficial microorganisms, such Vesicular-Arbuscular Mycorrhizae (VAM) and Trichoderma fungi, have been attributed to improve plant uptake of macro and micronutrients and enhance water availability. The main objective of this study was to examine the application of VAM and a commercial product, RootShield^TM containing Trichoderma harzianum, and fertilizer rates, on the growth and development of poinsettias. The study was conducted in the greenhouse in a complete randomized block design with four treatments (Control, VAM, RootShield^TM, and VAM plus RootShield^TM); two soil media (Sunshine Mix plus vermiculite and Promix Bx Mycorise Pro plus vermiculite); and three fertilizer rates (recommended rate, 75% recommended rate, and 50% recommended rate), with four replications each. Poinsettia cuttings, Poi Cortez Burgundy, were obtained from Greenstreet Grower, Inc. Treatments were added at the time of transplanting. Plant height, root length, color change, and shoot and root dry weights were determined. Fertilizer rate, soil type, and treatment influenced plant growth and development.  There was a significant difference in root dry weight and root length when fertilizer was applied at the 50% recommended rate, and a significant difference in shoot dry weight and shoot height when fertilizer was applied at 75% recommended rate.   For shoot heights, a significant interaction between treatment and fertilizer was detected, suggesting that treatment effect depended on fertilizer rate.  There was also a significant difference in plant color among soil types.  Changes in color were examined 23 days earlier in plants grown in Promix Bx Mycorise Pro when compared to Sunshine Mix. More studies will be conducted to further assess the effects of reduced fertilizer rates, beneficial microorganisms, and soil type on growth and development of poinsettias.