Commonly, plants need fertilizers containing three major plant food elements: nitrogen (N), phosphoric acid (P), and potassium (K). They are available in many different combinations and under a multitude of brand names.
Each brand should be analyzed on the label, indicating specifically how much water-soluble elemental nitrogen, phosphate, or potash is available in every pound of the product. The majority of these fertilizers are prepared with the ratio 20-20-20.
The first figure indicates available nitrogen; the second, available phosphate; and the third, water-soluble potassium. Commercial fertilizers used for house plants are sold in granular, crystalline, liquid, or tablet forms. Each should be used according to instructions on the package label or even more diluted
As a general rule, use a fertilizer recommended every 2 weeks from March to September. During the winter months no fertilizer need be added at all because reduced light and temperature result in reduced growth. Fertilizing at this time could be detrimental to some house plants. When applying fertilizer in a solution, make sure that some runs out of the bottom of the pot. This prevents root burn and the buildup of soluble salts or excess fertilizer and reduces the chance of burning the plant.