During the short days of winter, houseplants are not actively growing and experience a rest period. Thus, as plants are not actively growing during the winter, they typically need very little or no additional fertilizer. But now that spring is just around the corner and days are getting longer, now is the time to think about starting up a houseplant fertilization schedule.

To maintain health, most houseplants only need fertilizer once every 1-3 months, between March and September, as this is the time they are actively growing. Be sure not to over-fertilize your plants, as applying fertilizer too frequently can cause plants to outgrow their pots and space too soon. Too much fertilizer may also burn plant roots, particularly when growth is slowed if grown in dim light.

As fertilizers are composed of salts, over time, these salts can build up in the soil. To help prevent salt buildup, leach plant pots every 4-6 months to flush out the salts. Leaching is done by running a large amount of plain water through the pot, and allowing water to drain through completely. Be sure to empty plant saucers of excess water after leaching.

Fertilizers may be in the form of liquid, granular or tablets. Slow-release fertilizers may be mixed into potting soil at planting time or applied to the soil surface, and scratched in, with most lasting 3-4 months. Liquid fertilizers may be applied weekly in a diluted form, following label directions.

Did you know? Houseplants should be fertilized only when actively growing; those specially labeled for houseplants work well. A good N:P:K (nitrogen, phosphorus, potassium) ratio to choose is a 1:2:1, such as 5-10-5 or 10-20-10. A balanced ratio, such as 10-10-10, may also be used. Be sure to follow label directions and never use a stronger mixture than recommended.

Horticulture Questions? Contact McCormick at yvonne@iastate.edu for information or advice.