Fertilizing Houseplants

February is the ideal time to talk about fertilizing indoor plants. Most houseplants aren’t fed from September through January because they are resting in response to the short days. Yet in February the days begin to lengthen, and the added hours of daylight are a signal for many plants to grow. So it is fitting that we consider how to best add nutrients to our houseplants, along with other ways to keep them healthy and growing in this new year.

Here are some general tips for fertilizing your houseplants.

• Never fertilize a thirsty plant if you are using a synthetic fertilizer. Water your indoor plants well, then fertilize the next day. Liquid organic fertilizers can be added to the watering can.
• Some fertilizers might recommend that you fertilize every time you water, but this can build up salts in the soil and isn’t really necessary. Most houseplants do well when fertilized every three to four weeks.
• Topdressing the soil in houseplants with earthworm castings not only provides some gentle, organic nutrients, but helps keep the soil alive with beneficial micro-organisms. This can be done four times a year, adding about a quarter cup of castings for small to medium pots, and a half cup to a cup for large containers.

• Most indoor plants do well with a general fertilizer. Mix all plant food according to the directions: too much fertilizer will cause the tips and e edges of the leaves to turn brown. This is called “fertilizer burn.”
• Those who don’t want to mix powders into water can either use time-release, pelleted fertilizer or an organic granular product such as those from Espoma or the Coast of Maine Organic Plant Food. Note: if you use a granular organic that is sprinkled on the top of your soil, you’ll see the development of fungi etc that break such fertilizers down so that they can be absorbed by plants. If you sprinkle some potting soil over this it’s less noticeable, but in either case this is natural and not a problem.

Indoor plants that can be fertilized all year include orchids and citrus.

Know that fertilizer alone won’t keep a houseplant healthy and happy. Periodic repotting with fresh soil, correct watering, and the right amount of light are also important.