“N. P. K.” stands for the major plant nutrients used by growing plants. “N” is for nitrogen, which makes green color and growth. “P” is for phosphorus, which gives the plant sturdy growth, and “K” is for potash, which furnishes energy for over-all plant development.
There are also minor elements, numbering about fifteen in all. These include chemicals like iron, magnesium, boron, zinc, etc.
A package of fertilizer marked 5-10-5 expresses the percentage of each of the major elements, i.e., 5 percent potash.
Minor elements are usually included in most fertilizer formulas and may not be indicated by chemical names or percentages.
WATER-SOLUBLE forms of plant food are the most common and convenient to use for house plants such as 20-20-20 formula. They are sold as a powder, liquid or in tablet form. It is important to follow the manufacturer’s directions for mixing. But apply only at one half the rate recommended.
CONTROLLED-RELEASE FERTILIZER are favored by commercial plant growers, and some brands are now available in consumer-size packages. These formulas are designed so that one application will last from four to ten months, depending on formulation.
WATER-SOLUBLE TYPE: Potted plants growing in soilless potting mixes need more frequent applications than plants growing in potting mixtures containing soil. The design of soilless mixes affords better drainage and aeration, requiring more frequent watering, which results in faster leaching or loss of nutrients.
Artificially lighted plants may be fertilized once a month with a water-soluble fertilizer; plants under normal indoor light conditions, every two months. These are general recommendations. For individual plant recommendation, refer to culture.
DRY-GRANULAR TYPE: Apply once every four months regardless of light conditions. Use at the following rates of application:
A scant one third teaspoon per four-inch pot
One levelteaspoon per six-inch pot
One level tablespoon per eight-inch pot
CONTROLLED-RELEASE TYPE: Read the recommendations on the package before using. Where light intensity is high or a greenhouse is used for growing, it may be necessary to supplement with a water-soluble type.
A fertilizer is not a cure-all for plant trouble or a substitute for problems of water or light. An overdose of fertilizer or an application too often will damage or kill your plant. If in doubt – DON’T FERTILIZE.