Houseplant Fertilizers
by Pamela Kock

Feeding indoor plants is an important part in ensuring their health, longevity, and performance. With all the commercial plant foods available on the market, choosing the right fertilizer can be confusing. And what if you prefer to garden organically? Here is some information to take the mystery out of plant food.

Not all houseplants are created equal, nor are their requirements consistent throughout the year. Foliage plants have different needs than flowering plants. If fed improperly, flowering plants may not bloom as well. Most houseplants have a dormant season, or at least a period of slow growth, during which they need less water and fertilizer. Acid-loving houseplants such as azaleas will need a different formulation than those that prefer neutral or alkaline soil. These considerations should be kept in mind when choosing your plant food.

Houseplant fertlizers come in three basic types: time-release granules or spikes, liquid or water-soluble, and organic.

Many potting soil mixtures come with time-release granules already mixed in. This may seem to be a convenient solution, and for many plants it can work quite well. Time-release granules are formulated to work over a long period of time, from three months to a year. They’re good for folks who forget to fertilize their plants or don’t want to bother with regular applications. However, they’re hard to remove if the plant shows signs of being overfertilized. And since many plants prefer to be potbound and don’t like having roots disturbed, it can be difficult to use time-release granules on an ongoing basis. You can’t just scatter the fertilizer at the top of the pot. Time-release fertilizer spikes are another option, and often more convenient because they don’t require re-potting for use. Follow the directions on the package; simply push the spikes into the soil.

Liquid or water-soluble fertilizers allow much better control over the level of nutrients you administer. Some are pre-mixed, others are crystals that are easily dissolved. You can add a small amount to the watering can each time you water the plants for a safe, low level feeding, or use a larger amount every few weeks.

Organic fertilizers are more complicated, but can yield fantastic results. As with outdoor plants, many houseplants will enjoy a soil rich in organic matter such as manure or compost. Some organic advocates even suggest the addition of earthworms to houseplant soil. The problem is that in an indoor environment, these amendments may create unpleasant odors and unhygienic conditions. Adding fish emulsion may boost your plants, but the pots will smell terrible for a few weeks. Compost, when completely finished, doesn’t stink – but you may introduce insects, fungi, and mold to the home environment. If you do want to fertilize houseplants organically, the best way for beginners is to use a weak compost tea. Soak compost in a bucket of water for a few hours, then strain it to remove solids.

Before adding fertilizer of any kind, assess the plant’s needs and its condition. Many houseplants purchased from stores or nurseries arrive with time-release fertilizer already mixed into their soil. New plants shouldn’t be fertlized for a couple of months; this gives them time to acclimate to their new home. If your plant seems to be struggling, don’t fertilize until it begins to show signs of new growth. Plants need less fertilizer during seasons of dormancy or slow growth, and in the spring they will require a boost.

Signs of over-fertilization are leaves with browned tips, wilting of the plant, and dying new growth. Plants that need more fertilizer grow slowly, have yellow leaves, drop leaves gradually or have pale new leaves. In general, it’s better to err on the side of low fertilization than to over-fertilize – it’s easier to add nutrients than to take them away. If the plant has been over-fertilized, you can remove these chemicals from the soil by leaching. Place the pot in a stream of running water for a couple of hours.