How to Fertilize Your Orchid

By Steven A. Frowine and National Gardening Association

10 of 11 in Series: The Essentials of Growing Orchids

Many people think fertilizer is some type of elixir that will save even the most abused orchid. Actually, if the orchid is in poor health, fertilizers are rarely the answer. Fertilizers are most useful as a boost to help an already healthy orchid grow better.

The number and types of fertilizers on the market can make your head spin! You'll hear a lot of mumbo-jumbo about why one fertilizer is better than another. Fortunately, the choice isn't nearly as complicated as some manufacturers seem to make it.

If the orchid's roots are damaged, applying fertilizers will make the problem worse. If roots aren't functioning well, they can't absorb the fertilizer, and if the fertilizer isn't used by the orchid, it can accumulate in the orchid potting material. This buildup of fertilizer salts can further dehydrate and damage the remaining roots.

The following suggestions apply to most orchid-growing situations:

Look at the label and choose a fertilizer that has the words nitrate nitrogen or ammoniacal nitrogen, not urea: Although all forms can be used by plants, recent research shows that the nitrate and ammoniacal forms, not urea, are most beneficial to orchids.
Look for a fertilizer with 20 percent or less nitrogen: High amounts of nitrogen, much more than 20 percent, are not necessary to grow the best orchids no matter what media they are grown in. Too much of any nutrient cannot be used by the orchid plant and, as a result, merely ends up as a pollutant.
Don't worry about the amount of phosphorus in the fertilizer: It was earlier thought that a high-phosphorus fertilizer was necessary for better orchid bloom. This has now been found not to be the case.
In most cases, a fertilizer with supplementary calcium (up to 15 percent) and magnesium (up to 8 percent) is a real plus:
For most water sources, adding trace elements, including sodium, manganese, copper, zinc, boron, iron, and molybdenum, has been found to be beneficial to orchid growth: Don't worry about the exact amounts; just check the fertilizer container or label to see if they appear in small amounts.

Any fertilizer that meets these requirements will do. To find out if your chosen fertilizer does, carefully look at the fertilizer container. By law, the manufacturer is required to list what chemicals are included in the fertilizer.

Do not use water that has passed through water-softening units on your orchids. Such water may contain high amounts of sodium that can be harmful to orchids.

Here are some pointers to help you know when it's time to fertilize your orchid:

Fertilizing frequently at a more dilute rate is better than fertilizing less often at a higher concentration.
Never apply more fertilizer than is recommended by the manufacturer.
Drench the potting material, several times in a row, every few weeks or so with fresh water that contains no nutrients to wash out any excess fertilizer salts.
Very dark green leaves that are succulent and floppy can be a sign of overfertilizing.
When the orchids are actively growing, fertilize them.
If the orchids are diseased and in poor condition, stop fertilizing.