Houseplant Fertilizer Guide

Maybe you consider yourself a houseplant parent. If so, you’ve noticed caring for houseplants can be confusing, just like raising human babies. Houseplants don’t cry when they’re hungry or uncomfortable but respond to their environments in different and far more subtle ways. Knowing when it’s time to feed houseplants is challenging stuff, even for long-time houseplant growers. Let’s talk about the basic ins and outs of using houseplant fertilizer, another basic food for your ‘babies’ – the hows and the whens.

When to feed houseplants

We all know houseplants respond to water and sunlight or the lack of either of those things. They wilt when they need water. Their leaves grow pale and lanky when they aren’t getting enough sunlight. When the humidity is too low, they turn crispy; when it’s too high, they may develop rot. But, knowing when your houseplants need to be fertilized is far trickier.

There’s no clear signal from your plant that shouts “Hey, it’s time to feed me!”, other than perhaps slowed or stagnant growth, which for many houseplant parents, is barely noticed. So, whether you have the proverbial green thumb or a black thumb, you won’t be getting audible signals from your ‘babies,’ about feeding time.

Plants need fertilizer based on their growing cycle, and you’ll be happy to know that feeding coincides with the seasons of the year for most common houseplants. While your babies are inside where temperatures are more consistent, growing seasons influence houseplants much the same way they influence outdoor plants.

The best houseplant fertilizer schedules

Spring

Start fertilizing houseplants about 8 weeks before the last expected spring frost. The days begin to lengthen noticeably, and houseplants shift from a semi-dormant state into a period of active growth. The first three fertilizer mixtures/applications should be made at half the recommended strength. If it’s a granular product, use half the amount suggested on the label. If it’s a liquid houseplant fertilizer, mix it to half strength. This feeds houseplants at a time when they’re just gearing up for active growth and they don’t yet require large amounts of nutrients to fuel prolific growth.

Summer

When summer arrives, it’s time to switch to a more regular houseplant fertilizer program. Base the frequency of summer fertilizer applications on the type of fertilizer you’re using. Liquid fertilizers are applied more frequently; bi-weekly or monthly, for example. Granular products are used less frequently, perhaps once every month or two. Slow-release houseplant fertilizers break down slowly and release their nutrients in small amounts, over a longer period. A single application of most of these products lasts for three to four months.

Follow this schedule regardless of whether you move your houseplants outdoors for the summer. Houseplants are in a state of active growth when summer light levels are high, regardless of whether they’re exposed to the consistent temperatures of a home environment or the ups and downs of a patio or terrace environment.

Fall

About 8 weeks before your first expected fall frost, taper off your houseplant fertilizer amounts and frequency. Reduce the amount of fertilizer by half and start extending the amount of time between fertilizing for about 3-4 applications, which typically takes you to around the time of winter’s arrival.

Winter

Houseplants are not in a state of active growth during the winter and therefore should not be fertilized. Doing so can lead to fertilizer burn and brown leaf tips.

There are two exceptions to these rules.

First, if you live in a climate that does not receive regular winter frosts, continue to fertilize houseplants all winter long, but do it at half the strength and frequency of your summer applications. Again, this is due to light levels more than temperatures. Second, if you live in a tropical climate, where it’s warm all the time, keep your houseplants on a summer fertilization schedule year-round.

What’s in houseplant fertilizer?

Most houseplant fertilizers contain a mixture of both macro- and micronutrients. The three primary macronutrients, nitrogen, phosphorous, and potassium, found in a container of fertilizer are listed as a ratio on the front of the bottle or bag. Called the N-P-K ratio, these numbers tell you the percentage of each of those nutrients in the fertilizer.

Phosphorous—represented by the middle number on the container—is essential for flowering. Houseplant fertilizers for flowering plants should have a slightly higher amount of phosphorous in them (1-3-1, for example). Those used on green houseplants that don’t typically produce flowers, should be slightly higher in nitrogen, represented by the first number of the ratio. Fertilizers may also contain a balanced ratio of nutrients (5-3-3 or 5-5-5, for example). The best use of houseplant fertilizers with your ‘babies’ is choosing one for flowering houseplants and a separate one for non-flowering types. When you’re growing flowering houseplants like African violets, begonias, or gloxinia, using the right fertilizer is a smart way to go.

Many, but not all, fertilizers also contain secondary macronutrients, like calcium and magnesium, as well as micronutrients, such as iron, zinc, and boron. These nutrients are used in smaller amounts than the primary macronutrients of N, P, and K, but they are still essential to every plant’s ability to function using photosynthesis and their ability to deter pests and to withstand environmental issues. So, be sure your houseplant fertilizer contains a small amount of these nutrients as well.

Using a fertilizer formulated specifically for houseplants is a must. The ratio of macronutrients in a tomato fertilizer or a lawn fertilizer, for instance, is different than the ratio found in a houseplant fertilizer. All plant groups have different nutritional needs. Always look for some statement on the package confirming it’s for houseplants.

The ideal ingredients in houseplant fertilizers

The ideal houseplant fertilizer is made from naturally derived sources of these macro- and micronutrients, not made from chemicals synthesized in a laboratory. Though those blue, water-soluble fertilizers are commonly recommended, they aren’t the most eco-friendly source of nutrition for your plants, nor do they contain any micronutrients. Instead, turn to either a liquid or granular houseplant fertilizer made from natural ingredients to feed your houseplant babies.

A Recommendation

Liquid houseplant fertilizer

Liquid fertilizers should be used a bit more frequently than granular fertilizer. Examples of organic liquid houseplant fertilizers include Grow!, Espoma’s Indoor Houseplants, Liquid Love, and Jobes Water-soluble All-Purpose Fertilizer. They contain ingredients derived from plants and animals, as well as from mined minerals. Liquid fertilizers also come with a reduced risk of fertilizer burn.

Another benefit of using liquid fertilizers made from naturally occurring ingredients is that in addition to providing a houseplant with nutrients, they also act as growth enhancers. They are full of dozens of micronutrients, trace elements, vitamins, amino acids, and plant hormones, each of which plays a vital role in the health and vigor of your houseplants.

In Summary

Each houseplant variety has slightly different needs when it comes to houseplant fertilizer amounts and frequency, but there’s no need to overly complicate the process. You could study up on each individual houseplant species you care for, determining its specific nutritional needs, but most common houseplants have fertilizer requirements that are similar enough that treating them in a singular way is more than enough to satisfy their nutritional needs. Some houseplants are heavier feeders, but a feeding schedule like this one offers a good balance for your houseplant babies.