Indoor Plants | Fertilization
House plants need fertilizers containing three major plant nutrient elements: nitrogen (N), phosphorus (P), and potassium (K). These nutrients are available in many different combinations and under a multitude of brand names. The label on each product should indicate the percentage by weight of available elemental nitrogen, phosphate, and potash (potassium). Commercial fertilizers used for house plants are sold as liquids, granules, crystals, or tablets that are mixed with water for application, or as slow-release crystals and pellets that are placed on the soil surface or incorporated into the soil. Each should be used according to the instructions on the package label or diluted even more. Do not overfertilize because overfertilizing can kill house plants. See chapter 3, “Soil and Fertilizer Management,” for more information.
The frequency of fertilizer application varies depending on the purpose of the plant and the formulation of fertilizer used. If the plant is a nonflowering foliage plant and the desire is to keep it healthy at a given size, fertilization may be necessary every 4 to 6 weeks. However, if the plant is a flowering one or if the desire is to have the plant grow vigorously, then fertilizer may be necessary every 2 to 4 weeks. Use of slow-release fertilizers extends the above intervals by a factor of 3 to 4. When applying liquid forms of fertilizer, make sure that some solution runs out of the bottom of the pot. This technique prevents the buildup of salts (excess fertilizer) and reduces the risk of injuring roots and foliage.