Fertilizer for green plants: which natural or liquid fertilizer should you choose?

To feed an indoor foliage plant, choose a balanced fertilizer or one that is slightly higher in nitrogen, dilute it exactly as directed on the label, and apply it only while the plant is growing, to already moist potting mix. A natural fertilizer can do the job: compost, vermicompost, or liquid organic fertilizer really do nourish plants, more slowly than mineral fertilizers.

By contrast, most of the “homemade fertilizers” you hear about (coffee grounds, banana peels, eggshells, cooking water) provide little in a pot and come with risks. This guide explains how to read fertilizer labels and choose a fertilizer for indoor plants, which one to give each plant, how to measure the dose, and what the sources really say about natural fertilizers.

For a detailed month-by-month schedule, see our guide “When to Fertilize Your Indoor Plants”.

🌟 Why does an indoor foliage plant need fertilizer?

Because a pot is a closed environment. The RHS notes that plants growing in the ground often do not need fertilizer, whereas container plants do need feeding: their roots only have access to the nutrients in the potting mix. Fertilizer provides the three major nutrients—nitrogen, phosphorus, and potassium—and often trace elements as well.

According to the University of Connecticut Extension (UConn), many soilless potting mixes lack these trace elements, while organic fertilizers contain some or all of them. However, fertilizer is no substitute for light or proper watering: a plant that does not get enough light will not benefit from added nutrients.

📊 Natural, organic, liquid, or homemade fertilizer: an honest comparison

Here’s what store-bought fertilizers and the natural or homemade fertilizers most commonly recommended are really worth in an indoor pot. Each row is based on the sources cited in this guide; where no reliable source has measured an effect, we say so.

📋 Quick reference

Keep these guidelines in mind before every fertilizer application.

🪏 How to use liquid fertilizer for foliage plants, step by step

Liquid fertilizer is the easiest type to measure precisely indoors. UConn advises applying it only to potting mix that is already moist and following the label: most soluble fertilizers call for monthly applications, while smaller, more frequent doses provide a gentler, more gradual feed.

The RHS adds that liquid organic fertilizers act faster than dry organic fertilizers and are well suited to potted plants.

Spraying leaves does not replace applying fertilizer at the base of the plant: according to Linda Chalker-Scott of Washington State University, leaves cannot absorb enough material to meet the needs of the whole plant, and only trace elements can be effectively applied this way; nitrogen, phosphorus, and potassium are absorbed through the roots.

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🧭 Which fertilizer should you use for indoor foliage plants, Monstera, Hoya, or orchids?

There is no single perfect fertilizer for every plant, but a few simple rules can help. UConn says that foliage plants respond better to a fertilizer higher in nitrogen, and that for a mixed collection, a fertilizer with three similar numbers suits most indoor plants.

For flowering plants, sources highlight two nutrients: UConn mentions phosphorus, while the RHS mentions potassium. Specialty fertilizers, such as our liquid fertilizer for Hoya, have a higher potassium content.

📐 What do the N-P-K numbers on fertilizer mean?

The three numbers printed on the packaging give the percentages of nitrogen (N), phosphate (P), and potassium (K), in that order. According to UConn, they represent the dry-weight percentages of total nitrogen, available phosphate, and water-soluble potassium: a 20-20-20 fertilizer therefore contains 20% of each.

According to the RHS (Royal Horticultural Society), nitrogen supports the growth of leaves and stems, phosphorus supports roots and shoots, and potassium supports flowering, fruiting, and cold resistance. UConn cites 20-20-20 and 10-8-7 as examples of balanced fertilizers.

Our all-purpose fertilizer has an N-P-K of 4.9-2.6-3.9: a formula slightly higher in nitrogen, suitable for foliage plants. The numbers alone do not tell the whole story: a concentrated fertilizer needs to be diluted more, and the label specifies the dose.

📐 Natural or mineral fertilizer: what really changes?

To fertilize a plant naturally, use an organic fertilizer, also called natural or organic-certified depending on the label: according to the RHS, it comes from living things and may be plant-based (seaweed, nettle, comfrey) or animal-based (fish, blood, bone, poultry manure). Mineral fertilizer is made synthetically or derived from mined minerals.

The RHS makes a simple comparison: organic fertilizers are effective but generally less concentrated and slower, because soil organisms first have to break them down; mineral fertilizers are more concentrated and faster acting. In an indoor pot, solid organic fertilizer therefore takes time to work. Liquid organic fertilizers are an exception: they work faster and are suitable for pots.

Vermicompost, which UConn’s vermicomposting fact sheet describes as nutrient-rich, can be added to a potting mix.

Nettle manure tea is a different matter: in its opinion on a draft decree, ANSES (the French Agency for Food, Environmental and Occupational Health & Safety) assesses it as a plant protection product (a fungicide or “growth enhancer” sprayed on soil, and an insecticide against aphids and mites), and says not to “refer to properties of a fertilizer.”

It notes that “no studies allow its effectiveness to be assessed” and advises against applying it to flowering plants, as its high nitrogen content encourages foliage at the expense of flowering. For root health itself, see our article on mycorrhizae: the RHS also notes that excess nutrients inhibit mycorrhizal fungi.

📐 Coffee grounds, banana peels, eggshells: do these homemade fertilizers work?

These are the most widely shared “natural fertilizers,” but the sources are more cautious than social media. Regarding coffee grounds, the University of Arizona Extension notes that they contain nitrogen-rich proteins, but their pH varies from 4.6 to 8.4, so they are not always acidic.

She advises not to exceed 20% of the volume of a compost pile, as mixtures above 30% have often proved harmful, and to spread only a thin layer, since a thick layer of fine particles blocks water and air.

As for banana peels and eggshells, expert gardeners at the University of California (UC ANR) explain that bananas provide potassium, but their decomposition uses up nitrogen that the plant needs; eggshells, meanwhile, retain their calcium unless they are ground into a fine powder in an acidic environment (pieces were still there three years later), and plants rarely lack calcium.

Their advice for bananas: compost them, then apply the compost as a top dressing; the University of Arizona recommends the same approach for coffee grounds.

Indoors, there is an added risk: according to Oregon State University Extension, fungus gnat larvae live in roughly the top half-inch of moist potting soil and feed on decaying organic matter. As for cooking water, no reliable source has measured its benefits; if it is salted, never pour it into a pot.

🗓️ When should you fertilize a houseplant?

Only when it is growing. UConn places the active growing period between March and October and advises against fertilizing in winter, when light levels and temperatures drop.

The RHS takes the same view: almost no plants need fertilizer during the winter months, even if they flower at that time of year, and its December advice for houseplants recommends reducing watering and fertilizing as the days grow shorter.

The exact schedule depends on the fertilizer and the plant: our guide, “When to Fertilize Houseplants” provides a detailed schedule, while our winter houseplant guide covers cold-season care.

📅 Seasonal care calendar

🐛 Too much fertilizer: how to recognize and correct overfertilization

Excess fertilizer leaves telltale signs. According to the University of California’s “Soluble Salts” fact sheet, dissolved fertilizer becomes soluble salt that builds up in the pot as water evaporates; it slows growth, browns leaf tips, causes lower leaves to fall off, and forms a pale crust on the potting mix.

UConn adds that excess salts burn young roots and prevent the plant from taking up water, causing it to wilt even when the potting mix is moist.

The fix is simple: flush the pot with an amount of water equal to twice its volume, at least every 4 to 6 months, and never let the pot sit in its saucer; in cases of severe buildup, UConn recommends repotting in fresh potting mix.

🌿 Our houseplant fertilizers and guides

To learn more, here are our liquid fertilizers and the guides that complement this one, each linking to its own page.

🔑 Vitamins, tonics, and “boosters”: should you use them?

No, not to feed a plant.

Vitamin B1, often sold as a plant tonic, has no proven effect: according to the same University of Arizona Extension service, a healthy plant makes its own vitamin B1, and studies on woody plants, annual flowers, and crops have found no growth benefits.

Claims of “miracle growth” often come from in-vitro cultivation in sterile media, not from potted plants.

What is marketed as a “houseplant vitamin” is actually a complete fertilizer, light, and proper watering; for the water itself, see using rainwater to water your plants.

🔑 Our liquid fertilizers: what we know about their composition

For transparency, here is what our product pages say. Our all-purpose fertilizer lists an N-P-K of 4.9-2.6-3.9, with iron, magnesium, and zinc, described on its product page as micronutrients, and is dosed at 5 ml per liter of water; our Hoya fertilizer lists 3.5-3.4-5.1. The product pages do not specify whether the nutrients are organic or mineral-based, so we do not market them as natural fertilizers.

If you are looking for an organic option, compost, vermicompost, or a liquid organic fertilizer with a listed N-P-K are the safest choices. According to its product page, our all-purpose substrate contains micronutrients, mycorrhizae, and Bacillus bacteria; our full range is available in our fertilizers and plant care collection.

✅ Our method for feeding your houseplants

Remember three rules. Choose a fertilizer whose label lists a balanced N-P-K or one with slightly more nitrogen for foliage plants. Apply it only during the growing season, to moist potting mix, and at the recommended dose. Flush the pot from time to time to remove salts.

Natural fertilizers such as compost and vermicompost have their place when repotting; food scraps and coffee grounds, on the other hand, belong in the compost. And if your plant has stopped growing, check the light first: it determines whether the fertilizer will be useful.