Fertilisation Strategies in Organic Ornamental Plants

A reliable fertilisation strategy is the key to successful cultivation of organic potted plants. Potted plants were fertilised with solid fertilisers either 1) mixed in the growing media, 2) placed in the lower part of the pot (depot method), or 3) partly applied in a fertigation system after transplanting. Previous experiments showed that only 60-70% of organic nitrogen fertiliser could be accounted for (sum of plant uptake and mineralised nitrogen in growing media). Therefore, the amount of N-total applied per plant must be 1.4 to 1.6 times higher than the recommended rate with mineral fertilisers. In 12 out of 21 potted plant species tested over the last 12 years, organically fertilised plants showed at least the same quality as conventionally fertilised plants in terms of branching habit, numbers of flowers and root development. Lower plant quality in organic treatments was mostly related to the absence of chemical growth regulators. In most experiments, combined strategies with solid fertilisers (e.g., horn powder) and liquid fertilisers led to better quality plants compared with plants where all the fertilisers were mixed in the pot prior to transplanting. Organic fertilisers in Ebb-Flood irrigation systems (fertigation) must be carefully applied. The organic compounds normally start to ferment quickly and develop typically foul-smelling fermentation gases such as hydrogen sulphide. Of the liquid fertilisers evaluated, "Organic Plant Feed" (a concentrate of legume-based proteins) showed the best results in terms of plant performance, and had slower fermenting processes, especially compared to vinasse (a waste product of sugar processing). However, the development of foul-smelling gases in the irrigation water basin is not yet completely solved. Fertilising in other irrigation systems, such as drip irrigation or mat watering offer smaller challenges, compared with ebb-flood systems. Results demonstrate that a wide range of ornamental potted plants can be grown successfully using organic fertilisers.