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How and when do you fertilise houseplants?

Guidance verified against university horticulture extension sources and the RHS on 25 August 2026. Sources linked below.

Fertilise houseplants only while they are actively growing, typically spring through summer, using a balanced fertiliser diluted to half strength every two to four weeks. Skip it or cut right back in winter, when low light slows growth and the plant cannot use the extra nutrients. Too much fertiliser burns roots and leaf tips; too little shows up as pale, slow growth.

Do houseplants actually need fertiliser?

Yes, because a pot is a closed system with no way to replenish itself. Most potting mixes contain few or no long-term plant nutrients, and whatever is there gets used up or washed out with each watering, according to University of Connecticut Extension. A houseplant depends entirely on you to resupply nitrogen, phosphorus and potassium, the three primary nutrients it needs for leaf growth, root and flower development, and general stress tolerance, per the RHS.

What fertiliser should you use?

A balanced fertiliser labelled for houseplants, such as a 10-10-10 or 20-20-20 NPK ratio, suits most common houseplants, according to University of Connecticut Extension. The three numbers stand for nitrogen (leaf growth), phosphorus (roots and flowering) and potassium (overall resilience), per the RHS. General-purpose fertilisers sold for outdoor garden plants are formulated for faster growth than most houseplants need, so dilute them further than the label says rather than assuming a houseplant-labelled product and a garden product are used the same way.

When should you fertilise houseplants?

Fertilise while the plant is actively growing, which for most houseplants means spring through summer in the Northern Hemisphere. The RHS puts the UK growing season at roughly April to September, with monthly feeding for actively growing plants across that window. In Australia and the rest of the Southern Hemisphere, the same active-growth principle applies to the opposite calendar: spring and summer run roughly September to March, so that is when feeding does the plant the most good, tapering off through autumn and largely stopping over the Southern Hemisphere winter (June to August). No horticultural institution publishes an Australia-specific houseplant fertilising calendar; this is the same "feed during active growth" rule the RHS and US extension services state, applied to the Southern Hemisphere's reversed seasons rather than copied from a Northern Hemisphere source.

How much fertiliser should you use?

Dilute general liquid fertiliser to half or even quarter strength for houseplants, rather than the full rate on the label, according to Iowa State University Extension and Outreach: label doses are written for faster-growing outdoor plants, and most houseplants use nutrients more slowly. Monthly applications of a diluted liquid fertiliser through the growing season keep most houseplants healthy, per University of Maryland Extension. A weaker, more frequent dose and a stronger, less frequent one can suit the same plant; what matters is the total amount over a month, not any single feed.

Should you fertilise in winter?

Most houseplants need little to no fertiliser in winter. The RHS advises feeding at most once a month over winter, since light levels are usually too low for plants to use the fertiliser productively, and very few houseplants need any feed at all during this period. University of Nebraska-Lincoln Extension puts the underlying reason plainly: fertiliser applied to a plant that has slowed or stopped growing just accumulates in the soil as salt instead of being used. The exception is a plant that keeps producing new leaves through winter, common with monstera, pothos and philodendron in a warm, bright home: if it is still visibly growing, a light, reduced feed is fine; if it has stopped, hold off until new growth resumes.

What does over-fertilising look like?

Brown or crispy leaf tips and edges, a white or crusty salt build-up on the soil surface or pot rim, and wilting even though the soil is moist. Fertiliser dissolved in water is a soluble salt: as water evaporates between waterings the salt stays behind and concentrates in the soil, according to Oregon State University Extension Service, eventually making it harder for roots to take up water at all, a kind of drought despite wet soil. Washington State University Extension lists the same pattern: root damage, marginal leaf yellowing and stunting from salt build-up, plus direct leaf scorch where fertiliser has touched foliage. This is also a common cause of brown, crispy leaves, so if that is the symptom you are seeing, the full diagnostic guide covers it alongside humidity and water-quality causes.

Same species, three feeding levels: the visible difference is leaf size and colour on one end, tip burn and a soil-surface crust on the other.

What does under-fertilising look like?

Slow growth, weak stems, pale leaves and reduced flowering, according to University of Connecticut Extension. Nitrogen deficiency specifically shows first on the older, lower leaves as yellowing, because nitrogen is mobile inside the plant and gets reallocated from old growth to new, per Iowa State University Extension and Outreach. Rule out light and water problems first, since both cause similar pale, slow growth; if the plant is getting enough light and is not over or under-watered but still looks weak, an under-strength or absent feeding schedule is the next thing to check.

Liquid, granular or slow-release: which is best?

Houseplant fertilisers come in a few common forms, per University of Connecticut Extension: concentrated liquids or wettable powders mixed into water, time-release pellets or spikes pushed into the soil, and premixed liquids applied straight from the bottle. Liquid fertiliser is fast-acting and easiest to control the dose of, which is why it is the form recommended throughout this guide; the RHS notes it is generally the better choice for correcting a deficiency quickly. Slow-release pellets trade that control for convenience, feeding steadily over weeks to months without a schedule to remember, at the cost of being harder to stop quickly if a plant is showing signs of over-fertilising.

Should you fertilise a newly repotted or newly bought plant?

No, not straight away. Fresh potting mix already carries some nutrients, and roots disturbed during repotting take up nutrients more slowly while they recover, so fertiliser applied too soon can sit in the root zone rather than being used, adding to the risk of root damage instead of helping growth. Extension guidance is consistent on the underlying reason, feed only a plant that is actively taking up nutrients, even where a specific waiting period is not stated on an extension page. As a practical rule, hold off until you see new growth, usually a few weeks, then resume a normal feeding schedule.

How do you fix fertiliser burn?

Flush the soil with plenty of plain water to leach the built-up salts out. Water thoroughly, wait about five minutes, then water again and let the excess run freely from the drainage holes; the first watering dissolves the salts and the second carries them out, per University of Connecticut Extension and Iowa State University Extension and Outreach, which both recommend leaching as routine prevention every four to six months regardless. If a white or crusty deposit has formed on the soil surface or pot rim, scrape it away and top up with fresh, unfertilised mix, according to Colorado State University Extension. A pot with no drainage holes cannot be leached in place; in that case, ease the plant out, gently remove the old soil from the roots, and repot into fresh mix instead.

FAQ

How often should you fertilise a houseplant?

Every two to four weeks during active growth, usually spring through summer, using a balanced fertiliser diluted to half strength. Slow-growing plants and those in lower light need the lighter end of that range.

Should you fertilise houseplants in winter?

Most houseplants need little or no fertiliser in winter, because low light slows growth and the plant cannot use the extra nutrients. A plant that is still actively producing new leaves through winter can keep a light, reduced feed; one that has stopped growing should not be fed at all.

What are the signs of over-fertilising?

Brown or crispy leaf tips and edges, a white or crusty salt build-up on the soil surface or pot rim, and wilting despite moist soil. Flush the soil with plenty of plain water and cut fertiliser back, particularly outside the growing season.

Related guides

Sources

• University of Connecticut Extension, Soil Nutrient Analysis Laboratory: Fertilizing Houseplants
• Royal Horticultural Society: How to Feed Plants
• Royal Horticultural Society: Fertilisers, Types and Uses
• Iowa State University Extension and Outreach: How often should I fertilize houseplants?
• University of Maryland Extension: Fertilizer for Indoor Plants
• University of Nebraska-Lincoln Extension: Success With Houseplants, Fertilization
• Oregon State University Extension Service: Soluble Salts Damaging to Houseplants
• Washington State University Extension, Hortsense: Fertilizer Burn
• Iowa State University Extension and Outreach: Identifying Plant Nutrient Deficiencies, Nitrogen
• Colorado State University Extension, PlantTalk Colorado: Leaching Salts from Potting Mixes