If their other requirements are met, orchids will grow and flower for fairly long periods without fertilizer.
Witness the people in tropical areas such as South Florida who grow them mounted on trees and let nature do the rest. Indeed, that is how epiphytic orchids grow in nature. But hobbyists generally try to give their orchids more than the bare minimum so that the plants flower at or above their potential.
There are many different points of view on how to fertilize orchids and what fertilizer to use. Everyone has a favorite fertilizer or supplement. There are so many variables that how and when you fertilize depends on what kinds of orchids you grow and how and where you grow them. This article will offer a brief explanation and general guidelines on fertilizing orchids. For more specific application, join your local orchid society and ask someone there who grows the same kind of orchids as you. It is unlikely that you will kill any orchids with orchid fertilizer so following the recommendations here will provide your plants needed nutrition.
If you are a gardener you are probably familiar with the N-P-K listings on fertilizer bags. Orchid fertilizers have them too. Let’s go over these three elements and see how they affect plant growth. Nitrogen (N) helps make plants green and helps them grow faster. It is the element responsible for vegetative growth (the leafy parts). Phosphorus (P) is good for root growth, disease resistance, seed and fruit growth, and especially for blooming and flowering. Potassium (K) helps with increasing root growth, drought resistance and disease resistance.
Types of Fertilizers
There are three main types of fertilizers used for orchids: balanced, high nitrogen and bloom booster.
Balanced fertilizers have been traditionally recommended for use with orchids potted in inorganic potting media such as lava rock and Aliflor, and tree fern (which has fallen out of favor due to conservation concerns). Plants mounted on cork bark or other substrates also benefit from using a balanced fertilizer. An example of a balanced fertilizer would be represented by the numbers 20-20-20.
High-nitrogen fertilizers have long been recommended for use with orchids potted in fir bark or fir bark mixes. The reason for extra nitrogen is that the bacteria that cause the bark to decay use up much of the available nitrogen, thus depleting the orchid. This practice has recently come into question. Nonetheless, using a high-nitrogen fertilizer, especially in spring at the beginning of the growing season, can promote strong vegetative growth under ideal conditions. An example of high-nitrogen fertilizer would be 30-10-10.
Bloom or Blossom-Booster Formulas
Bloom or blossom-booster formulas are high in phosphorus. Typically, high-phosphorus fertilizers are applied every other week for four to six applications the season before expected bloom. For winter–spring blooming orchids, bloom booster is usually applied in the autumn. Vandaceous hybrids and other orchids that bloom throughout the year can be given bloom booster every third or fourth fertilizing. An example of a bloom booster would be 10-30-20. Fertilizers used on orchids should contain little or no urea. This is because soil organisms must first convert the nitrogen in urea to a form useable by plants, and since orchids do not grow in soil, this conversion does not occur efficiently.
How To Apply Fertilizer Application
How fertilizer application is applied varies as much as orchids themselves. Typically, plants are fertilized once a week during spring and summer and every two weeks in the autumn and winter. Regardless of the fertilizer that you choose, most experienced growers use ½ the label-recommended strength. Remember, in nature epiphytic orchids’ roots are exposed and the only nutrients they receive are from bird and animal droppings, decaying insects and detritus. The old saying about fertilizing orchids is: Feed them weekly weakly. Fertilizer is best applied in the morning on sunny days. For mounted orchids, or orchids with exposed roots, such as vandas in empty baskets, many growers routinely first water the plants and then follow with fertilizer a half hour later. The watering before fertilizing prepares the spongy velamen of the orchid roots to better utilize the fertilizer. Orchids in pots are usually not watered first but some growers have their own techniques.
There are requirements specific to certain orchids. For instance, do not fertilize nobile-type dendrobiums after early autumn. This rule actually applies to all orchids that have decided rest periods and all deciduous orchids. Fertilizing them while in their rest period keeps them in continual growth instead of resting before producing flowers. In other words, you may get a lot of growth and no flowers.
There are also many secret recipes growers use that supposedly produce stronger plants or more flowers. Certainly, vitamins and micronutrients are as essential as the building blocks of plant growth mentioned above. Elements such as magnesium, boron, calcium, carbon and others are required for strong plant growth. All in all, although there are certain practices that are documented as being helpful, it has not been proven that supplements actually contribute to improved growth in orchids — but it probably doesn’t hurt to use them.
From the April 2013 issue of Orchids Magazine
Prepared by the AOS Education Committee with Photographs by Greg Allikas