House Plant Fertilizer: The Nutrition
Your Plants Need for Good Health

While light gives plants the energy they require, house plant fertilizer provides the nutrients they need to grow healthy and strong.

How to Choose House Plant Fertilizer

The fertilizer you need depends on your plant. Read the labels carefully. They usually list three numbers, such as 10-20-10. These are (in order) the percentages of nitrogen, phosphorus, and potassium (often called potash) that make up the major nutrients in the house plant fertilizer. And here's what they do:

Nitrogen gives the plant lush, green foliage and promotes growth.

Phosphorus keeps roots strong and healthy, and encourages flowering.

Potassium makes stems strong and helps fight off diseases.

Fertilizers specially formulated for flowering plants will contain less nitrogen and more phosphorus and potassium. You'll even find some labeled for specific plants, such as orchids.

Most house plants need a balanced fertilizer such as a 10-10-10 formula.

In addition to nitrogen, phosphorus, and potassium, plants need small amounts of other nutrients, or trace minerals -- called micronutrients.

You'll find some of these minerals, such as calcium, magnesium, and sulfur in good-quality potting mixes. And even smaller quantities of copper, iron, and zinc. However, plants that aren't repotted very often will need fertilizer to replenish their supply of micronutrients.

fertilizer granules, house plant fertilizer

Water-soluble fertilizers are the most common and are easy to use. You'll find them in the forms of liquid, powder, or crystals. Manufacturers often suggest to use the maximum amount that a healthy plant can tolerate. This sells a lot of fertilizer, but may be too much for your plant. As a general rule, I use only half the recommended amount.

Slow-release granules (shown at left) are easy to use because you just sprinkle them on top of the soil and they'll dissolve when you water your plant.

fertilizer spike, fertilizing house plants

Fertilizer spikes (at left) work the same way, but are inserted into the soil. Push spikes fairly deeply into the soil near the edge of the pot to avoid damaging the plant's roots.

Although the roots are responsible for taking in nutrients, the leaves can also absorb them. Foliar feeding is a quick way to revive a plant that has been deprived of nutrients. Most fertilizers will scorch leaves if they are sprayed directly on the leaves, but foliar feeds are made to be applied this way.

How to Know When Your Plant Needs Fertilizing

Here are some clues:

  • Weak new growth
  • Pale leaves
  • Dropped leaves
  • Weak stems
  • Small or no flowers

Too Much of a Good Thing is...Well, Too Much

Whoa, there gardener! Many indoor gardeners mistakenly believe more is better when it comes to fertilizing house plants. The truth is, far more plants suffer from too much fertilizer than lack of it. Excess fertilizer can burn roots and leaves. When in doubt, use less.

How do you know if you've over-fertilized your plant? Look for these symptoms:

  • Scorched edges or brown spots on leaves
  • Misshaped leaves
  • Wilting leaves
  • White crust on the surface of the potting mix

If you want to know how often to fertilize your plant, look it up in the House Plants Encyclopedia A-Z.

Bottom-Line Fertilizing Guidelines

  1. Never feed a new or newly repotted plant. A plant that relocates from the garden center to your home is stressed and will need a month or two to adjust to its new environment. Good potting mixes contain nutrients to feed a repotted plant for several weeks.

  2. Don't use as much house plant fertilizer as recommended on the label. For some reason, manufacturers suggest the maximum amount that a healthy plant can tolerate. I generally use half that amount.

  3. Fertilizer is not a cure-all for an unhealthy plant. Never feed a plant that's suffering from root damage, disease or insects.