A heatwave doesn't have to be a disaster for the veg patch. Most edible plants are tougher than they look in 30°C — what they need from you isn't fuss, it's a few sensible changes and the discipline not to panic. Here's what actually helps, what's a waste of effort, and which alarming-looking problems will sort themselves out once the weather breaks.
01Water in the morning, deeply, at the base
If you change one thing, change when you water. The RHS is clear that early morning is the best time: there's less evaporation, and the plant has the whole day to use what you've given it. Watering in the evening leaves foliage and soil damp overnight, which is an invitation to slugs and fungal disease; watering at midday mostly waters the air.
Water thoroughly but less often rather than a daily splash. A proper soak sends roots down to find moisture and makes the plant more drought-tolerant; a light sprinkle keeps roots near the hot, dry surface where they suffer most. And aim the water at the soil, not the leaves — wet foliage in humid heat spreads disease, and droplets don't feed the roots anyway.
02Mulch is the cheapest heat protection there is
After you've watered, cover the bare soil with a 5–7.5cm (2–3in) layer of organic matter — homemade compost, well-rotted manure, even grass clippings will do. It slows evaporation, keeps the roots cooler, and saves you watering runs. This is the single best-value thing you can do in a hot spell, and it costs nothing if you've got a compost heap.
03Containers are the first to suffer
Pots, growing bags and window boxes dry out far faster than open ground — in a real heatwave they can need watering every day, sometimes twice. Check them by pushing a finger into the compost; if it's dry below the surface, water. Two free tricks that genuinely help: group containers together so they shade each other and create a slightly more humid pocket, and stand thirsty pots on saucers during the worst days so they can draw water back up. Move what you can into afternoon shade.
04Salads and herbs will try to bolt — keep them cool and cut them
Heat and dry soil push leafy crops to "bolt" — shoot up, flower and turn bitter. Lettuce, spinach, rocket and coriander are the usual casualties, and the RHS notes that dry soil in particular brings it on. You can slow it down by keeping the soil consistently moist, throwing some shade netting or fleece over the row during the hottest part of the day, and harvesting little and often — picking leaves delays flowering. If a crop bolts anyway, pull it, sow a fresh batch for later, and don't take it personally. Basil actually enjoys the warmth more than most leaves, but it will still run to seed if it dries out, so keep it watered and pinch the tops out regularly. (See the basil profile and, for a container herb that wilts fast in heat, mint.)
05Tomatoes: two heat problems, one fix
When it gets very hot, tomato flowers often drop off without setting fruit. This looks like failure but usually isn't yours — extreme heat interferes with pollination, and fruit set simply resumes once temperatures ease. Don't rip the plant out.
The problem genuinely worth preventing is blossom end rot — that sunken, leathery brown patch on the bottom of the fruit. It isn't a disease and it isn't a pest; it's a calcium-delivery failure caused by the soil drying out and rewetting. As the RHS explains, calcium can only reach the far end of the fruit if there's a steady flow of water through the plant, so the fix is boringly simple: keep the compost consistently moist and never let it dry out completely. Tomatoes in growing bags and pots are the most at risk because their roots have the least buffer. Mulch the surface, water regularly, and you'll dodge most of it. (More on the tomato profile.)
06Don't feed a plant that's struggling in the heat
There's a temptation to reach for the tomato feed when things look stressed. Resist it on dry soil — the RHS advises only ever applying liquid feed to compost that's already moist, and piling on high-nitrogen feed during a heat-and-drought spell can actually make blossom end rot worse by pushing soft new growth that demands even more calcium. Water first, feed second, and ease off entirely on the most brutal days.
You do not need to spend anything to get through a heatwave. Water-retaining gel crystals get marketed hard every summer; we'd skip them — a 2–3in mulch and a consistent watering habit do the same job for free and improve your soil while they're at it. The same goes for "anti-transpirant" sprays and self-watering gadgets: grouping your pots, mulching, and standing them on saucers costs nothing and works. Spend your money on a decent watering can rose or a hose trigger if you must — the rest is just stuff.
07And look after yourself
Water the garden at dawn or dusk and you'll be out of the worst sun too. The plants can wait for the cool of the morning; so can the weeding.
How we checked this
Every care and safety claim on this page is verified against horticultural and veterinary sources.
Sources: RHS — Watering Wisely · RHS — Watering vegetables and fruit · RHS — Blossom End Rot · RHS — Bolting in Vegetables · Purdue University — High Temperature Effects on Tomato Fruit Set
Checked 19 July 2026. If our advice ever conflicts with the RHS, believe them and tell us.