There is a debate among orchid growers over whether or not fertilization is necessary. If grown in bark, organisms in the bark quickly cause it to break down and release natural organic nutrients usable by your orchids. Some people who fertilize think that chemical fertilizers are superior to organics. Understanding organic fertilizers for orchids are a good way to decide if, and how, to fertilize your orchids.
Fertilizers are labeled using N-P-K numbers, which refer to their percentage of nitrogen, phosphorus and potassium. The higher the number, the higher the percentage of that particular nutrient. Balanced fertilizers will have equal numbers for all three values.
Orchids in Soil
Some orchids grow well in soil. If you are growing orchids in soil, add 60 to 70 percent organic matter as fertilizer to the soil before planting your orchid. Good organic fertilizers are peat, well-rotted compost or partially decomposed bark. These materials will quickly decompose and offer good nutrition for your orchids. If you want to fertilize further, use a 1-1-1 balanced orchid fertilizer.
Orchids in Other Media
If growing orchids in other media, such as bark or peat, those orchids will have natural organic fertilization delivered by the media as it decomposes. Because the microbes that help to decompose the bark compete with the plant for nitrogen resources, you might consider using a commercial 3-1-1 orchid fertilizer with orchids grown in this fashion.
Orchids do best in soil with a pH of between 5.5 and 6.3. You can apply a slow-release organic fertilizer every few months, or a fish emulsion or compost tea every two weeks.
Organic vs. Chemical
Some orchid growers believe that if you're growing in organic media, you do not need organic fertilizers. The logic is that the frequent waterings orchids require will wash the organic fertilizer out of the pot before it can be absorbed. Some people feel that the only effective fertilizers for orchids are chemical fertilizers that are already in a form usable by the orchids. However, in nature, orchids rely entirely on organic fertilizers. While chemical fertilizers may help a problematic plant, organic fertilizers can help reduce problems with overfertilization and fertilizer burn.