It’s a perennial effort to help your little ones grow up — whether a fern, fiddle-leaf fig, succulent, or sansevieria — as plant parents know very well. And keeping plants happy and healthy sometimes takes a little more than some sunshine, the perfect planter, or even a full watering can. To get the right bloom or blossom, a fertilizer might just be what your plant needs to thrive. Any good plant owner should make sure ferns, succulents, and sansevierias get plenty of sunshine and just the right amount of water. This basic care will keep plants alive, but if you really want them to thrive you might consider fertilizer.
While fertilizer is often referred to as plant food (it’s usually marketed that way, anyway), that’s not entirely correct. “Plants get their food from photosynthesis, but they need some other micronutrients and macronutrients that are critical in creating enzymes, regulating water, [and] plant defense,” says Summer Rayne Oakes, author of the forthcoming book How to Make a Plant Love You and host of the YouTube series Plant One on Me. Instead, think of it this way — plants need to get their veggies in, too. Fertilizer is similar to the supplemental vitamins and minerals we take. “If we don’t get enough calcium or B vitamins, our health suffers,” explains Kristin Monji, founder of landscaping firm Birch and Basil Design. “For plants, sunlight is food which provides the majority of their sustenance, but they still need additional vitamins and minerals like we humans do in order to have optimal health.” That’s similar to what Gabi Stone, the garden manager on the design and build team at Brooklyn Grange, says: “Plants require fertilizer because outside of their native environments or in cultivation, their specific food needs are not as readily available. Fertilizers are an easy and effective way to supplement these deficiencies.”
Fertilizer features three main macronutrients plants need: nitrogen, phosphorus, and potassium. These will be represented on product labels by the acronym NPK. You can also find an assortment of micronutrients in them, with some more specialized formulas including minerals like calcium and magnesium, according to blogger Erinn Witz of Seeds and Spades. But it’s the big three that are worth paying attention to, as several of our experts stressed. All fertilizer is labeled with numbers representing the balance of these three elements. A 10-10-10 fertilizer, for example, is composed of 10 percent of each. “Nitrogen helps with leaf growth and stem growth, phosphorus helps with root growth and flowering, and potassium helps the plant fight disease,” Will Axelrod, who also works as a project manager at Brooklyn Grange, told us. And yes, you can tell which letter your plant lacks with just a look: Leaf discoloration and stunted growth are hints of a nutrient deficiency, Witz says. Generally, Witz describes, the color of the leaves will give it away: yellow means it needs more nitrogen, green or purple for phosphorus, and brown edges for potassium.
The right NPK ratio depends on the needs of your weeds (or leaves). “If you’re trying to fix a specific issue with your plants related to the lack of one of these elements, you’ll obviously want a formula that’s rich in that particular one,” Witz advises. But one that’s between 5 to 15 “for each of the three elements is usually a pretty safe bet for routine use,” she adds. Broadly speaking, a balanced formula — for example, one that’s labeled 10-10-10 — works well for most plants, according to both Witz and Diane Kuthy, the founder of How to Grow Everything. Of course, that advice only hits the surface of what fertilizer is best for your plants. To dig deeper, we asked experts to explain the best fertilizer formulas for everything from orchids to cacti.
Best all-purpose fertilizers
When it comes to fertilizers, you want to avoid over-fertilizing (just like an overdose of vitamins isn’t great for us, either). Less is more, so it’s important to follow what the package says for application amounts, according to Monji. That’s a sentiment shared by many of the experts we talked to (more on that below). Monji recommends this all-purpose fertilizer from FoxFarm, particularly for its slow-release formula. “You can think of fertilizers the same way as human food — slow food versus fast food, if you will.” Whereas synthetic fertilizers are like fast food, slow-release fertilizers are similar to slow food, with nutrients released every watering, taken up by plants naturally, and lasting for months (so less need to keep applying), Monji explains. This fertilizer is also OMRI (which stands for the Organic Materials Review Institute) certified, which is “the gold standard for products in the horticulture industry,” Monji points out.
“Many houseplant folks will be fine giving their indoor foliage plants a well-balanced fertilizer,” says Oakes, meaning one in which the three macronutrients are present in equal amounts. She recommends Jack’s, “a synthetic fertilizer that also has some critical micronutrients.” Since one of the most common beginner mistakes is over-fertilizing, which can actually burn your plants’ roots, Axelrod stresses that “it’s very important to be conservative when fertilizing.” You’ll add a pinch of this fertilizer to a gallon of water before applying to your plants, and Oakes says you can start with half the amount indicated on the label to be safe. “Generally you’ll want to only fertilize maybe once a month with the fertilizer diluted in your watering can,” says Axelrod, and he recommends taking a break in winter when plants aren’t using up as much light energy.
Another way to avoid over-fertilizing is choosing a product with low percentages of each macronutrient. Susannah Strazzera, a horticulturist at Wave Hill public garden and culture center in the Bronx, says she loves Dyna-Gro’s all-purpose fertilizer “because the numbers are low, and when people are first starting out with fertilizing they tend to use too much. If you use too much nitrogen you get stretchy growth and that attracts aphids and other insects.” Stretchy growth refers to too much space between the leaves. “You want to have a tight, full plant,” says Strazzera. “You don’t want to have a long, stretchy plant.”
Chantal Aida Gordon and Ryan Benoit of the gardening and design site The Horticult, and authors of How to Window Box, like Maxsea’s balanced fertilizer as a go-to option for most houseplants. They explain that for common leafy plants (like ZZ plants and philodendron), you want fertilizer with a good amount of nitrogen to promote leaf growth.
[Editor’s note: This fertilizer is on back order at the moment, and Amazon doesn’t say what day specifically it will be available to ship.]
This fertilizer is one of Witz’s recommendations for herbs, vegetables, or other nonflowering plants. “It has a pretty balanced NPK blend, so it’s great for supporting your plants without going overboard in any one nutrient.” She appreciates Dr. Earth as a brand, too, for its use of organic ingredients and consistent production of high-quality products. “These aren’t the cheapest products out there, but I believe the quality is well worth paying a little bit more.”
Best fertilizers for flowering plants
Because phosphorus is the macronutrient most responsible for flowers, Gordon and Benoit recommend looking for a fertilizer with a higher middle number for flowering plants like African violets and medinilla. Strazzera likes Blossom Booster, a product in which, she says, “the nitrogen is low. Nitrogen is to make green stuff like stems and leaves. So now that your stems and leaves are made, it’s mature … and it’s ready to make flowers.” She says a dose of Blossom Booster when plants are starting to bud will help produce bigger, healthier, and longer-lasting flowers.
Monji agrees that flowering plants need higher levels of phosphorus. “Plants need phosphorus in order to flower properly, and if they’re lacking in it, they won’t set buds, flower, or set seeds. It’s vital to photosynthesis as well and a host of other functions besides flowering, which is why it’s part of the NPK trinity.” She raves about this fertilizer: “I haven’t found a flower yet that doesn’t enjoy Flower-Tone.” For even more of a boost (it’s called the Blossom Booster, after all), Monji mixes this fertilizer with the aforementioned Plant-Tone in flower gardens and perennial orders. Stone also gave this fertilizer a stamp of approval, calling it “good in promoting healthy flowering.”
Sara Gatanas, who handles special events and public relations at Urban Garden Center, likes the all-natural, liquid concentrate fertilizer Flowers Kiss from FoxFarm for flowering plants like orchids and tropical plants. “It provides just enough nitrogen and micronutrients to help grow throughout the season,” she says.
[Editor’s note: This spray is on back order at Amazon with no official restock date, but you can find a larger version of this concentration available at Wayfair.]
Dimitri Gatanas, who also works at Urban Garden Center as general manager, says this concentrate is a “high-demand fertilizer” in the store and that “we have trouble keeping this product on the shelves.” Gatanas points out two ingredients in this fertilizer in particular: bat guano and earthworm castings, which help provide an “excellent source of nitrogen, phosphorus, and potassium.” The two also act as soil conditioners and improve drainage. “Gardeners swear by it,” Gatanas adds. “In basic terms, it provides the best mix of NPK to give your flowering plants the strength to produce flowers.”
Best fertilizer for cacti and succulents
Compared to foliage and flowering plants, you’ll want to look for something lower in nitrogen for your cacti. “With cactus and other succulents, like sansevierias [and] snake plants, use a balanced liquid cactus fertilizer at quarter strength of what is says on the label,” advise Gordon and Benoit.
Best fertilizer for vegetables and herbs
Witz heard through the grapevine — her fellow gardening friends — that Dr. Earth made “awesome products,” so when she saw this fertilizer in-store, she picked up a bag for her vegetables that she suspected were low on calcium. The formula is specifically designed for vegetables and herbs, which might come in handy for those who have an indoor garden.
Best organic fertilizers
Since indoor houseplants are already in an artificial setting — without the naturally occurring microbes found outdoors — it’s less vital to use organic fertilizer in potted plants, although it does have some advantages. According to Oakes, “plants don’t really distinguish between organic and synthetic fertilizers, but organic fertilizers tend to build up the soil, helping promote healthy microbial activity.” Another benefit of choosing organic fertilizer is that the percentage of each macronutrient is usually lower than in synthetics. “Organic fertilizer is typically more gentle and it’s not easy to over-fertilize your plants,” says Oakes. For an organic option, she likes this one from Espoma.