How to fertilize houseplants

Newly potted plants need no fertilizing, but the nutrients in the soil will soon need replenishing. Fertilize only during the growing season and never when the roots are very dry.

Most plant foods contain three major nutrients-nitrogen, phosphorus, and potassium-in various ratios. Most houseplants flourish on the usual 1530-15 blend, but flowering plants benefit from a high-potassium formula such as 8-6-12 (sold as tomato food). To keep foliage plants lush, use fish emulsion or another high-nitrogen fertilizer instead of a balanced blend for every fifth feeding.

Plant-food concentrates are safe as long as their solutions are not too strong; too much fertilizer can damage a plant’s roots. It is generally better to dilute a fertilizer to half the recommended strength and apply more often. For a quick tonic to an undernourished plant, spray the foliage with liquid fertilizer diluted to one quarter strength. Time-release pills and spikes give long-lasting nutrition. Following the directions on the package, poke them into the soil away from the roots.