How to Care for Houseplants in a Heatwave

Most houseplants come from warm parts of the world, so a bit of heat is not the enemy — many actually grow faster in summer. The problem with a heatwave is not the temperature itself so much as what comes with it: fierce light through the glass, compost that dries out in hours rather than days, and, indoors, the drying blast of air-conditioning. Get ahead of those three things and your plants will sail through the hottest week of the year. Here is how to help them do it.

Move plants off hot windowsills

The single most damaging spot in a heatwave is a windowsill in direct sun. Glass magnifies the heat, and leaves pressed against or close to it can scorch within an afternoon, developing pale, bleached or crispy patches that never recover. Move plants back from south- and west-facing windows during the hottest weeks, especially between midday and mid-afternoon when the sun is strongest. If you cannot move them, a sheer curtain or blind filters the harshest rays without plunging the room into darkness. Sun-lovers such as cacti and succulents cope far better than thin-leaved tropicals like calatheas, ferns and prayer plants, which are the first to suffer.

Water more often — and water in the morning

In a heatwave the compost dries out much faster, so a plant that was happy on a weekly water may now need checking every couple of days. Do not simply water more on a fixed schedule, though — check the top two to three centimetres of soil with a finger and water thoroughly when it is dry, letting the excess drain away completely. The best time is early morning, before the day heats up: the plant goes into the hot hours fully charged, and less water is lost before the roots can take it up. Terracotta pots dry out fastest of all, so keep a closer eye on anything in unglazed clay.

Raise the humidity, but skip the misting myth

Heat, and especially air-conditioning, strips moisture from the air, and tropical foliage plants that want 50% humidity or more feel it quickly as crispy tips and edges. Grouping plants together, standing pots on a tray of damp pebbles, or running a small humidifier all raise the local humidity in a way that lasts for hours. Misting, by contrast, raises humidity for only a few minutes and can even encourage fungal spots on leaves left wet in still, warm air — so it is pleasant but not a real fix. Group your humidity-lovers together and let them share a more forgiving microclimate.

Mind the air-conditioning

Air-conditioning is a mixed blessing for houseplants. It keeps the room from cooking, but it also removes humidity and creates cold, dry draughts that tropical plants dislike as much as they dislike heat. Keep plants out of the direct line of AC vents, where the constant cold blast can cause drooping and leaf drop. The aim in a heatwave is a stable, comfortable room — not a plant swinging between a hot window and an icy draught several times a day.

Hold off on repotting and heavy feeding

A heatwave is the wrong moment to repot. Disturbing the roots when a plant is already fighting to keep itself hydrated adds stress on top of stress, and a freshly repotted plant is far more likely to wilt in the heat. Wait for a cooler, settled spell. Feeding is more nuanced: plants growing actively in the warmth do use nutrients, but a heat-stressed, wilting plant cannot make use of fertiliser, and feeding dry roots concentrates salts that can scorch them. Feed only healthy, well-watered plants at normal or half strength, and skip it entirely for anything that is struggling.

Know the signs of heat stress

Catching heat stress early lets you act before damage sets in. Watch for these signals:

• Wilting or drooping in the afternoon that recovers overnight — a plant losing water faster than it can replace it.
• Leaf edges curling inward or upward, a common way plants reduce the surface exposed to heat.
• Pale, bleached or brown crispy patches where direct sun has scorched the tissue.
• Flower buds or flowers dropping prematurely, a classic stress response.
• Fast-drying soil and a suddenly light pot, telling you the watering rhythm needs to change.

A warning about plants outdoors

If you move houseplants outside for summer, a heatwave is exactly when they are most exposed. Plants that have lived indoors are not acclimatised to direct sun and can scorch badly in a single afternoon, and outdoor wind dries them out even faster than indoor air. During extreme heat, move any holidaying houseplants into shade, water them more often, and bring the most delicate ones back indoors until the weather breaks.

The heatwave checklist

To sum it up: pull plants back from hot glass, water thoroughly in the early morning and check the soil far more often than usual, raise humidity with trays and grouping rather than misting, keep everything out of both direct afternoon sun and cold AC draughts, and postpone repotting until the heat passes. Do those things and a heatwave becomes a week of fast growth rather than a week of casualties.

Not sure whether a wilted, patchy leaf is heat scorch or something else? Photograph it in PlantMe and let the app compare it against its library of common plant problems — it will tell you whether you are looking at sun damage, thirst or a disease, so you can respond correctly rather than guessing in the heat of the moment.