Potting mix contains enough nutrients for roughly two to three months. After that a plant is living on whatever you give it.
That said, underfeeding is a slow problem and overfeeding is a fast one. A plant that is never fed grows slowly. A plant that is fed too much burns its roots.
What the numbers mean
Every fertiliser carries three numbers, such as 10-10-10 or 20-5-10. They are the percentages of the three main nutrients, always in the same order.
- N, nitrogen drives leaf and stem growth. The one that matters most for foliage houseplants.
- P, phosphorus supports roots and flowering.
- K, potassium supports general health, water regulation and disease resistance.
Which to buy
A balanced feed where the three numbers are equal or close suits almost every foliage houseplant.
Reach for something different only in two cases. A higher-phosphorus feed encourages flowering on Anthurium, Hoya and Peace Lilies. A high-nitrogen feed pushes leafy growth, which is rarely needed indoors and often produces weak, stretched stems.
How much
Half the strength stated on the bottle, most of the time.
Fertiliser instructions are written for garden plants growing hard in full sun. A houseplant in an indoor light level cannot use that much, and the excess accumulates in the soil as salt.
For slow growers, quarter strength is closer. That includes ZZ plants, Snake Plants, Cast Iron Plants and the jewel Alocasia.
How often
Spring and summer
Every 2-4 weeks for most foliage plants. Fast growers like Monstera, Pothos and Syngonium sit at the frequent end, and slow growers at the other.
Autumn and winter
Nothing, for almost everything.
Growth slows or stops, so the plant cannot use what you give it and the salts build up around roots that are least able to cope. The exception is a plant under grow lights that is still actively producing leaves.
Never feed a struggling plant
Feeding does not help a plant recover from rot, cold damage or dormancy. It makes all three worse. Fix the underlying problem and feed once it is growing again.
Salt build-up
Unused fertiliser leaves mineral salts behind. Over time they accumulate, and they draw water back out of the roots rather than letting it in.
Signs:
- A white or yellowish crust on the soil surface or around the drainage holes
- Brown, crisp leaf tips on a plant with good humidity
- Growth slowing despite regular feeding
Flushing the pot
Two or three times a year, take the plant to a sink and run water through it steadily for a minute or two, letting it drain freely. That dissolves the build-up and carries it out.
Do this before you resume feeding in spring.
Types of fertiliser
Liquid
Mixed into water. Easy to control, easy to dilute, and it acts immediately. The best default for houseplants.
Slow release granules
Mixed into the soil, releasing over months. Convenient, but you cannot dial them back once they are in, and they keep releasing through winter when you do not want them to.
Organic options
Worm castings, seaweed extract and similar. Gentler, harder to overdo, and they feed the soil rather than the plant directly. Slower to show results.
Plants that want very little
Some houseplants evolved on poor soil and are damaged by ordinary feeding schedules. Feed these twice a year at most, at quarter strength:
- ZZ Plant
- Snake Plant
- Cast Iron Plant
- Ponytail Palm
- Jade and most succulents
- Hoya
And two that are sensitive to fertiliser salts specifically, showing it as brown leaf edges within weeks: Calathea and Maranta. Quarter strength, monthly in summer, nothing else.