Heatwave plant care: how to protect plants in extreme heat

Signs of heat stress

Plants show heat stress in fairly predictable ways. Check them in the early morning: a plant that is still wilted at dawn needs help now, while midday drooping that recovers by evening is often a normal water-saving response.

When and how to water in a heatwave

Water early in the morning, when the soil and air are coolest and less is lost to evaporation. Water deeply so moisture reaches the whole root zone, rather than a light splash every few hours.

• Aim at the soil, not the leaves; drops on leaves in hot sun do little and wet foliage encourages disease.
• Small pots may need a second watering in the late afternoon; check them with your finger first.
• Soil that has dried hard sheds water. Water slowly in two or three passes so it soaks in.
• Prioritize: new plantings, pots and fruiting vegetables first; established shrubs and trees can usually wait.

⚠️ Avoid watering in the hottest midday sun only when you have a choice; if a plant is collapsing, water it immediately, whatever the time.

Shading plants: cloth, sheets and timing

Temporary shade during the hottest hours (roughly late morning to late afternoon) lowers leaf temperature and water loss. A light shade cloth that blocks 30–50% (estimated) of sunlight suits most vegetables and flowers; denser cloth can cut growth too much.

Good options

• Commercial shade cloth (30–50%, estimated) on a simple frame.
• An old light-colored sheet or fine net clipped to stakes.
• Patio umbrella or a beach parasol moved during the day.

Keep in mind

• Leave space for air to flow; do not wrap plants tightly.
• Shade from the west side in the afternoon matters most.
• Remove shade when the heatwave ends so plants get full light again.

Group pots, move them and mulch

• Group pots together: they shade each other and the humid air between them reduces water loss.
• Move pots on castors or by hand into morning-sun, afternoon-shade spots, and lift them off hot paving.
• Dark pots heat up quickly; wrap them or set them inside a larger, light-colored pot.
• Mulch beds and large pots with 2–3 in of straw, bark or compost, keeping it a little away from stems. It keeps roots cooler and slows evaporation.

Balconies and terraces: reflected heat

Balconies and terraces are often several degrees hotter than the garden. Walls, glass and tiles store heat and reflect it back onto the plants, and the air is usually windier and drier.

• Pull plants a little away from bright walls and railings that face the afternoon sun.
• Put pots on wooden slats or a mat so they are not sitting on hot tiles.
• Use a light screen or an outdoor blind on the sunniest side.
• Rinse the floor with water in the early morning to cool the area briefly, but avoid letting water drip onto neighbors below.

Houseplants during a heatwave

• Move plants a little back from south- and west-facing windows; glass intensifies heat and can scorch leaves.
• Close a light curtain or blind during the brightest hours to filter the sun.
• Keep plants out of the direct stream of air conditioners and fans, which dry leaves quickly.
• Indoor soil dries faster in a heatwave; check it more often, but still water only when the top layer is dry.
• Clustering plants slightly raises the humidity around them.

Hold off on fertilizer and pruning

A stressed plant cannot use extra nutrients. Fertilizer can push soft new growth that scorches easily, and salts in dry soil can burn roots. Wait until temperatures drop and the plant is growing well again.

Hard pruning exposes inner stems and fruit to sunburn. Limit yourself to removing dead or broken parts. Also postpone repotting and new planting until cooler weather.

Step-by-step heatwave plan

When a heatwave is forecast, work through this list:

1. 2–3 days before: Water beds and pots deeply and add mulch where it is missing.
2. Prepare shade: Set up shade cloth, sheets or umbrellas for sensitive plants and vegetables.
3. Move pots: Gather containers in a sheltered, afternoon-shade spot and lift them off hot surfaces.
4. Harvest: Pick ripe or nearly ripe vegetables and herbs before the peak heat.
5. During the heatwave: Water every morning where needed and check small pots again in the late afternoon.
6. Skip: No fertilizer, pruning, repotting or new planting until it cools down.
7. Afterwards: Remove shade gradually, inspect damage and resume normal care.

Recovery after the heat

After the heat breaks, give plants a week or two before judging the damage. Many will push new leaves from buds that looked lost.

• Trim fully brown, crisp leaves and dead flower stems; leave partly damaged leaves, they still feed the plant.
• Return to your normal watering rhythm gradually and check that pots are not now staying too wet.
• Resume feeding at half strength once new growth appears.
• Lettuce or spinach that has bolted is best pulled and resown when it is cooler.

Your own safety comes first

Garden work in extreme heat is risky. Do your watering, shading and moving early in the morning or in the evening, and stay indoors during the midday heat.

• Wear a hat and light clothing, and drink water regularly.
• Heavy pots are harder to lift when you are hot and tired; ask for help or use a trolley.
• Metal tools, hoses and furniture left in the sun can become hot enough to burn skin.

⚠️ Watch for signs of heat illness such as dizziness, headache or nausea. Stop, move to a cool place, drink water and seek medical help if you do not improve.

Frequently asked questions

Plants to watch in hot weather

TomatoLettuceBasilHydrangeaOlive TreePepperPeace lilyGeranium