An Evaluation of Organic Fertilizers for Use in Container Media

The “organic” movement in the United States has gained considerable momentum over the last ten years.  Consumers now consistently choose organically grown produce from supermarkets and restaurants.  Gardeners have also adopted “organic” products.  These are mostly fertilizers used in gardens or as container fertilizers.  Gardeners are faced with a plethora of products to fertilize plants. Yet, efficacy testing is largely missing from the retail product market.  Also, since there are many different and varied sources for fertilizer ingredients there are just as many possible mineral release possibilities.  While organic fertilizers are generally believed to be “slow release” there is potential for nutrient loss from containers because organic fertilizers tend to be applied at higher rates or more frequently than soluble fertilizers.  We investigated the effects of several fertilizer products, and a few experimental products, on their effects on the quality, growth, and chlorophyll content (via SPAD chlorophyll meter) of petunia and basil.  The project was repeated for a second trial using broccoli and snapdragon plants.  During the first trial, the two experimental products produced the greatest number of flowers on petunia, and the greatest quality on both petunia and basil.  Chlorophyll content was not associated with quality in the first trial.  In the second trial, the organic product Gro Power (solid and liquid forms) produced the greatest number of flowers, quality, and SPAD readings for both snapdragons and broccoli.  For both plants, the untreated and ammonium sulfate treatments produced the lowest quality, least amount of flowers, and lower SPAD readings than other organic treatments.