How do I look after houseplants in a heatwave?
Indoor plants face a combination nothing outdoors does — glass magnifying the light, no air movement, and very dry air. Which of those is actually damaging yours, and what to change.
- Difficulty
- beginner
- Time
- 15 min
- Read
- 5 min
Short answer
Move plants back from south and west-facing windows, where the glass concentrates heat and light far beyond what most houseplants evolved for. Water when the compost is dry rather than on a schedule, group plants together to raise humidity, and do not feed or repot anything that is struggling.
Most houseplants are understorey species from humid forests. A sunny British windowsill in August gives them the opposite of everything they are adapted to: intense direct light, very dry air and, in a closed room, still hot air with no movement. The good news is that all three are easy to fix and none of them requires buying anything.
Step by step
- Move plants away from the hot windows.South and west-facing glass in summer delivers direct sun far stronger than the dappled light most houseplants come from, and the glass concentrates heat immediately behind it. A metre back into the room, or behind a sheer curtain, is a completely different environment. This alone solves most heatwave houseplant problems.
- Watch for scorch on the leaves.Bleached or brown papery patches on the upper surfaces of leaves facing the window are sun scorch. It does not spread and the damaged leaves will not recover, so move the plant and leave the leaves alone — they still photosynthesise around the damage.
- Water by checking, not by schedule.In heat, plants use more water, so the interval shortens — but a schedule is still the wrong tool. Push a finger into the compost to the second knuckle; water thoroughly if it is dry, leave it if it is damp. More houseplants are killed by watering on a fixed day than by drought.
- Water thoroughly and let it drain.Water until it runs from the bottom, then tip away what collects in the saucer after half an hour. A pot standing permanently in water rots. A pot given a splash every day is dry at the roots and wet on top.
- Raise the humidity by grouping.Standing plants together creates a more humid pocket, because each plant transpires into the shared air. Standing pots on a tray of damp pebbles — with the pot base above the water, not in it — does the same. Both are considerably more effective than misting, which evaporates in minutes.
- Get some air movement.Still, hot air is a problem for houseplants as well as people. Gentle air movement helps them regulate temperature and reduces fungal problems, but do not aim a fan directly at a plant, which dries it out. Air moving in the room is enough.
- Stop feeding anything that is struggling.Fertiliser salts in dry compost draw water out of roots and make heat damage worse. Feed only plants that are visibly growing well, and stop entirely for anything wilting, scorched or checked until it recovers.
- Do not repot in a heatwave.Repotting damages roots at the moment the plant most needs them. Unless the compost has become completely water-repellent and will not accept water at all, wait for cooler weather.
- Be careful about putting houseplants outside.A summer outdoors genuinely benefits many houseplants, but a plant moved from indoors straight into sun scorches within hours. Move it to full shade first, then increase light over a fortnight, exactly as you would harden off a seedling.
- Watch for pests, which multiply faster in heat.Red spider mite in particular thrives in hot dry indoor air and is a classic heatwave arrival — look for fine webbing and a stippled, dusty look to the leaves. Raising humidity is both prevention and part of the treatment.
Tips
- Cacti and succulents are the exception on light, but even they can scorch if moved abruptly from a shaded spot into a hot south-facing window.
- Terracotta pots dry faster than plastic, which is useful for plants that hate wet feet and a nuisance in a heatwave for thirsty ones.
- A plant that wilts, is watered, and does not recover within a few hours has a root problem rather than a water problem. Check whether the compost is actually wet.
- Rooms left closed all day while everyone is out get much hotter than rooms in use. Plants in an unused spare room often suffer worst.
- If you are going away, move houseplants off windowsills into the middle of a cool room, group them together and water them thoroughly first. They will cope with lower light for a fortnight far better than with heat.
Common mistakes
- Leaving plants on a sunny windowsill through a heatwave — Glass concentrates heat and light well beyond what understorey plants tolerate, and the air trapped against the glass is hotter still. Moving them back into the room fixes most problems at once.
- Watering more often on a fixed schedule — Heat changes how fast compost dries, so the interval changes daily. Checking the compost takes seconds and prevents both drought and rot.
- Misting to raise humidity — The effect lasts minutes. Grouping plants together or using a damp pebble tray raises humidity for hours and actually works.
- Putting houseplants straight outside into sun — They scorch within hours. They need hardening off in shade over a fortnight, exactly like seedlings.
Questions people ask
Should I move my houseplants away from the window in summer?
For most, yes. Direct summer sun through glass is far stronger than the light most houseplants evolved under, and the air immediately behind the glass is hottest. A metre into the room, or behind a sheer curtain, suits the majority.
How often should I water houseplants in hot weather?
Whenever the top few centimetres of compost are dry, which in heat may be twice as often as usual — but check rather than assume. Water thoroughly until it drains, then empty the saucer.
Can I put my houseplants outside for the summer?
Many benefit from it, but they must be acclimatised: full shade first, then gradually more light over about a fortnight. Straight from a living room into sunshine causes severe scorch.
Why do the leaves have brown crispy edges?
Usually dry air, irregular watering or fertiliser salt build-up rather than heat alone — the guide on brown leaf tips covers reading the pattern. In a heatwave all three become more likely at once.