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, 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, fertilizer contains the three main macronutrients plants need: nitrogen, phosphorous, and potassium (represented on product labels as NPK), plus an assortment of micronutrients. Will Axelrod, head gardener of the Design/Build arm of Brooklyn Grange, explains, “Nitrogen helps with leaf growth and stem growth, phosphorus helps with root growth and flowering, and potassium helps the plant fight disease.”
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. Different fertilizers offer different ratios, which can make it confusing to choose what’s best for your plants. We asked experts to decode the labels and break down the best formulas for everything from orchids to cacti.
Best all-purpose fertilizers
“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.
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.
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.
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 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 Epsoma.
Axelrod also likes organic fertilizer because its low nutrient concentrations are more gentle on plants. “We like Neptune Harvest fish and seaweed emulsion,” he says. “It has a low NPK ratio, 2-3-1, and it’s organic.” Gatanas agrees that it’s an “awesome, natural organic fertilizer.”
Best fertilizers for home-gardening pros
If you’re really serious about your plants and are attuned to their different needs, Gatanas recommends this kit with 12 of FoxFarm’s most popular fertilizers. “It comes with a whole bunch of different fertilizers all in one big set so you have different ones for vegetables, houseplants, and different stages of growth,” she says. “It’s kind of cool if you’re into gardening and you’re going to have multiple types of plants.”
It’s not technically fertilizer, but experts also recommend adding compost to your soil for added plant nutrition. “Compost and compost tea are also great and often overlooked additives for indoor plants,” says Axelrod. “Organic matter is as important to your plants as NPK, which is abundantly found in compost or worm castings.” Gordon and Benoit like this surprisingly “non-stinky” biodynamic compost because it’s “nearly impossible to overfertilize with and provides a natural time release of nutrients with every watering.”
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