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Houseplant fertilizer basics: How and when to feed houseplants
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Being a houseplant parent can be confusing business! Unlike human babies, houseplants don't cry when they're hungry or uncomfortable. Instead, they respond to their environment in different, far more subtle, ways. Knowing when it's time to feed houseplants is challenging stuff, even for long-time houseplant growers. Today, I'd like to review the basic ins and outs of houseplant fertilizer, and cue you in on how and when to feed your houseplants.
When to feed houseplants
Houseplants 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, instead of waiting for a signal from the plant, you'll have to take matters into your own hands and use houseplant fertilizer on a schedule that's based on their growing cycle.
The timing of houseplant fertilizer applications should follow the seasons and their growth habits.
Each specific houseplant has slightly different needs when it comes to houseplant fertilizer amounts and frequency, but there's no need to overly complicate the process. Yes, you could study up on each individual houseplant species you care for, determining its specific nutritional needs, but the truth is that the vast majority of 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 than others, it's true. But, a houseplant fertilizer schedule like the one found below, offers a good balance that both satisfies heavy feeders and keeps you from going overboard with those houseplants that require lower amounts of fertilizer.
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Here's the best fertilizer schedule for most common houseplants. It's based on the cycle of the growing season, which, though they are inside where temperatures are more consistent, influences houseplants much the same way it influences outdoor plants.
Water-soluble liquid houseplant fertilizers are applied only during periods of active growth.
The best houseplant fertilizer schedule
In a bit, I'll discuss different houseplant fertilizer products mentioned here and how to apply them, but here's the low-down on when they should be used.
Spring houseplant fertilizer schedule:
- Start fertilizing houseplants about 8 weeks before the last expected spring frost. For example, here in Pennsylvania, where I live, the danger of spring frost typically passes around May 15th. This means I begin to fertilize my houseplants in mid-March. This is when the days begin to lengthen noticeably and houseplants shift from a semi-dormant state into a period of active growth.
- The first three fertilizer 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 (more on these two types of fertilizers in a bit). This feeds houseplants at a time when they're really just gearing up for active growth and they don't yet require larger amounts of nutrients to fuel prolific growth.
Summer houseplant fertilization schedule:
- 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 of time. A single application of most of these products lasts for three to four months.
Liquid organic houseplant fertilizer is a great choice because it's made from naturally derived ingredients.
- Follow this schedule regardless of whether you move your houseplants outdoors for the summer or not. 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 sitting out on a patio or terrace.
Fall houseplant fertilization schedule:
- About 8 weeks before your first expected fall frost, taper off your houseplant fertilizer amounts and frequency. At my house, that means starting in mid-August, I reduce the amount of fertilizer by half and start extending the amount of time between fertilizing for about 3-4 applications, which typically takes me to about the time of winter's arrival.
Winter houseplant fertilization schedule:
- None. 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 (more on why this happens here).
Don't fertilize houseplants, such as this large spotted Dieffenbachia, during the winter when they're not in a period of active growth.
Two exceptions to these rules:
- 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.
- And, 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 inside the container. The ratio of these macronutrients in a tomato fertilizer or a lawn fertilizer is different than the ratio found in a houseplant fertilizer as each of these groups of plants has different nutritional needs. This means using a fertilizer formulated specifically for houseplants is a must. That should be the first thing you look for when purchasing houseplant fertilizer. It should say "for houseplants" somewhere on the packaging.
The ratio of N-P-K is on the label of every houseplant fertilizer. This one is higher in P, making it good for blooming plants like African violets.
Phosphorous (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. They may also contain a balanced ratio of nutrients (5-3-3 or 5-5-5, for example). I typically use one houseplant fertilizer for my flowering houseplants and a separate one for non-flowering types. This isn't necessary unless you're growing flowering houseplants like African violets, begonias, or gloxinia.
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 metabolic pathway. You'll want to be sure your houseplant fertilizer contains a small amount of these nutrients as well.
Houseplants won't tell you when they need to be fertilized, so you'll need to put them on a schedule.
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.
Organic plant fertilizers are made from plant-, animal-, and mineral-based components.
Types of houseplant fertilizer
Now that you know when to fertilize houseplants and what nutrients houseplant fertilizers should contain, it's time to look at the different types of houseplant fertilizer to determine which one is right for you.
Liquid houseplant fertilizer
They need to be used a bit more frequently than granular fertilizer, but organic liquid houseplant fertilizers are my personal favorites. Brands like Grow!, Espoma's Indoor Houseplants, Liquid Love, and Jobes Water-soluable All-Purpose Fertilizer 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.
Organic liquid houseplant fertilizers are made from liquid kelp, fish emulsion, compost tea, worm tea, liquid bone meal, rock phosphate, plant extracts, and humic acids, to name just a few.
Liquid and water-soluble houseplant fertilizers are mixed with irrigation water and applied to plants.
Granular houseplant fertilizer
Granular fertilizers for houseplants are found in one of two formulations: as loose, granular pellets or as compressed fertilizer "spikes." Pelletized granular fertilizers for houseplants, such as Organic Plant Magic and Be-1, are sprinkled on the surface of the soil. Compressed fertilizer "spikes," such as Jobes Organic and EarthPods, are pushed down into the soil to come in close contact with plant roots.
The best pelletized and compressed granular houseplant fertilizers are made from naturally derived ingredients. These include dehydrated worm castings, bone meal, blood meal, sulfate of potash, limestone, rock phosphate, and other animal-, mineral-, and plant-based ingredients. Synthetic chemical-based granular fertilizers are available for houseplants, too, though I avoid them. A quick check of the ingredient list on the label tells you what the fertilizer is made from. If you don't see any ingredient list at all, it's a synthetic fertilizer.
Houseplant fertilizer spikes are easy to insert into the soil.
Slow-release houseplant fertilizers
Also called time-released fertilizers , slow-release houseplant fertilizers are made from a synthetic source of nutrients. The liquid nutrients are encapsulated in a coating. This coating breaks down slowly and releases the nutrients in low doses over a long period of time. Products like these mean you'll be fertilizing less frequently. It's very convenient, but do be aware that they aren't made from eco-friendly ingredients.
The coating on slow-release fertilizers mean the nutrients are available to plants for a long period of time. However, they are chemically derived.
Houseplant fertilizer in a nutshell
As you can see, fertilizing houseplants doesn't have to be an overly complex practice. Use the right products and apply them according to a seasonal schedule, and your houseplant family will be as happy and healthy as can be.
For more on houseplants, check out the following articles:
Apartment Plants: The best houseplants for apartment living
Fertilizer numbers and what they mean
Air Plant Care: How to tend, water, and fertilize Tillandsia
Tips for repotting a Phalaenopsis orchid
The best low light succulents
How do you feed your houseplants? We'd love to hear about it in the comment section below.
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