Plant fertilizers, including those for orchids, contain three main elements that affect plant growth. Nitrogen (N) is the element that helps with leafy or vegetative growth. Phosphorous (P) is especially good for blooming, as well as for root growth and disease resistance. Potassium (K) promotes root growth and disease and drought resistance. Take note, however, that any fertilizer used on orchids should contain little or no urea.
By reviewing the numbers related to these three elements (N-P-K), you’ll find there are generally three types of fertilizers used for orchids.
- Balanced fertilizer, represented by numbers like 20-20-20, is good for mounted orchids or those potted in inorganic potting media like expanded clay.
- High-nitrogen fertilizer, 30-10-10 for example, is good to use at the beginning of the orchids’ growing season. It may also be more beneficial for orchids potted in fir bark mixes than balanced fertilizer.
- High phosphorous fertilizer, like 10-30-20, often known as bloom booster, is typically applied every other week for four to six applications before the plant is expected to bloom.
How to apply these fertilizers to your orchids varies as much as the orchids themselves. In most cases, following the old saying “feed orchids weekly weakly” will work well. Preparing the fertilizer at ¼ to ½ the label recommended strength would result in a weak solution to apply weekly.
Keep in mind that certain orchids have specific requirements. For example, orchids with a definite rest period like deciduous orchids should not be fertilized after early autumn. Continuing to fertilize and regularly water these types of orchids will keep them in active growth rather than providing the needed rest before producing flowers.
The best advice: if in doubt, ask someone who grows the same kind of orchids as you.