How and When to Fertilize Houseplants

Most folks already know how important it is to give houseplants the right amount of water, light, and high-quality potting mix, but they don’t automatically think of plant food. Your beloved houseplants need nutrients to grow strong and healthy. 

But wait, you might say. Doesn’t a good potting mix already contain nutrients? It sure does, but as your plants grow, they use up those nutrients, so they must be replaced. Also, watering can deplete them. 

What is Plant Fertilizer?

So, what is plant food? Also sometimes referred to as fertilizer, it’s a collection of nutrients essential to plant growth. The “macronutrients” are the ones your plants need the most; they include nitrogen (N), phosphorus (P), and potassium (K). 

• Nitrogen is needed for leaf growth and greening of the plant.
• Phosphorus is necessary for strong root production and flowering.
• Potassium is important for overall plant health. 

For more on NPK and the nutrients plants need, look at this helpful article.

Every package of plant food lists the ratio of N:P:K on the package, but you don’t have to worry about that when you’re growing houseplants. Just make sure you pick a plant food designed specifically for houseplants (or indoor plants)—it should say that right on the label. You can also get plant food designed especially for specific types of plants, like orchids or succulents.

Types of Houseplant Fertilizer

There are three main types of houseplant food: liquid, water-soluble, and stakes. 

1. Liquid plant food is ready to use and can be applied directly to the soil every week or two, depending on the instructions.
2. Water-soluble plant food should be mixed in with the water in your watering can so you can feed and water at the same time, again every week or two. 
3. Indoor plant food stakes are meant to be buried in the soil where they’ll release plant food slowly over a month or two—again, check the label of the specific brand you’re using.

When to Fertilize Your Houseplants

The colder months can be thought of as a bit of a hiatus for your houseplants. With the changes in temperature and available light, growth will naturally slow down, and that’s a good thing—plants need rest, too! 

So, you only want to feed them during the months they’re actively growing, which usually means spring (March) through early fall (October). Of course, for houseplants that bloom in the winter, the timing should be adjusted to match the growing period.

One caveat: If you’ve just potted your plant in a new potting mix that already contains fertilizer, wait 4 to 6 weeks before feeding with additional plant food.

How to Fertilize Your Houseplants

The most important things we can say here are to use plant food meant for houseplants and read the label! The plant food amount and frequency will vary depending on what houseplant food you use, so be sure to follow directions and don’t overdo it. 

Fertilizing too much or too often can cause leaves to turn yellow or brown (or even fall off) and can make roots more prone to disease.

Here’s how to feed:

1. Wait for the morning, as daytime is better for moisture absorption. 
2. Apply plant food to the soil according to the directions.
3. Water your plant as you normally would. Of course, if you’re using a water-soluble fertilizer, you’ll already have that part covered.
4. Set a reminder for yourself for the next time to feed.

While all houseplant foods can be applied to the soil, many water-soluble plant foods can also be applied foliarly, which means spraying it on the leaves. The advantage of foliar feeding is that the nutrients are absorbed much more quickly and can go to work right away, so it’s useful when you’re looking for quick growth or the plant is blooming. This works particularly well with high-humidity tropical plants (like monstera or calathea) that enjoy being misted regularly.

Making the time to feed your houseplants regularly is an easy way to help ensure they continue to grow strong and beautiful—in other words, a little nourishment can go a long way. It’s simple to do and only takes a moment, so go on, feed those hungry houseplants!

We’ve got tips on feeding your outdoor garden, too. Check out How and When to Fertilize Your Vegetable Garden and Fertilizing Containers: Tips for Feeding Plants in Pots.