Documents: Special Interest: Orchids:

Orchid Fertilizer Guidelines
by Marilyn Light
November 13, 1999

Orchids like other houseplants need mineral nutrients with which to grow. Orchids that grow continuously such as Phalaenopsis and Paphiopedilum need year-round feeding but seasonally dormant orchids such as Pleione do not. Orchids require the same basic nutrients as other flowering plants but because orchids are usually grown in bark chips and not in soil, they require more careful feeding. Plants should be watered before applying fertilizer so as to avoid root damage.

Fertilizers are formulated about three primary nutrients, N (nitrogen) P (Phosphorus and K (Potassium. The proportion of available nutrient in each category is presented in a standard way, N-P-K such as 20-20-20. While the proportion of N-P-K is given in this formulation no information is available concerning other essential micro-nutrients such as Magnesium or Iron. These may or may not be present in the commercial product. Orchids do need micronutrients and so it is best to look for a product that provides these substances.

A good rule of thumb is to use liquid fertilizer products to feed orchids. Such products should contain micronutrients. Avoid using preparations which contain urea. Use products such as 7-7-7 to promote general growth and products with more Phosphorus in proportion to Nitrogen to promote flower production. An example of a flower promoting fertilizer formulation is 3-12-6. Always dilute the product according to manufacturer's instructions. It is better to fertilize weakly than to apply a lot at one time. Fertilizer solution can be applied to the pot or can be safely sprayed onto leaves provided the solution is not too concentrated. One-quarter to one-half teaspoon of liquid product (7-7-7) can be diluted in one gallon of water and applied once a week when plants are actively growing. Once every four weeks, flush the pots with plain deionized water or rainwater to dissolve any excess mineral salts that may have accumulated in the medium.

If a plant is flowering size, fertilizer products designed to promote flowering can be applied, several months before blooming could begin. It is important to realize that besides fertilizer, other factors that could affect flower production include 1) having adequate light, 2) being exposed to the appropriate temperature regime, and 3) being exposed to the appropriate day length.

Copyright Marilyn H.S. Light 1997

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