How to protect plants in a heat wave
Water, shade and what not to do when it's very hot
Signs of heat stress
Long spells above 90°F (32°C) slow plant growth, and stress shows quickly. Watch for these signs.
- Wilting in the hottest part of the day, with recovery in the evening.
- Leaves that roll or cup, or dry out along the edges.
- Sunscald on fruit, and flowers or young fruit dropping off.
- Lettuce, spinach and other cool-season crops running to seed.
Water deeply and early
Water in the morning, at the base of plants, and deeply enough to wet the soil at least 6 inches (15 cm) down. Check the soil an inch or two below the surface first.
Hanging baskets and pots dry out much faster than garden beds, and may need water every day. Water wilted plants as soon as you reasonably can.
Shade and cool the roots
Keeping roots cool and moist is half the battle.
- Mulch beds with straw or compost to slow evaporation and keep soil temperature even.
- Hang shade cloth on a frame above tender plants; it can be up to 10°F (5.6°C) cooler underneath.
- Move pots into shade, and away from hot walls and paving.
- Indoors, pull plants back from hot, sunny windows.
- Shade young seedlings and lettuce with row covers or cloth during hot spells.
Fruit that won't set
Tomatoes and peppers drop their blossoms when days stay above about 85–95°F (29–35°C) and nights above about 70–75°F (21–24°C). The heat spoils the pollen. Keep plants watered, and fruit sets again once it cools.
What to avoid
Don't transplant, prune or feed during extreme heat. Stressed plants can't use the food, and pruning can expose shaded leaves to sunburn. Hold off on pest sprays too: many can damage plants when temperatures stay above 80°F (27°C), so wait for cooler weather.
Look after yourself
Garden early in the morning, before the hottest part of the day. Drink plenty of water, and wear a hat and sunscreen. The plants can wait.
Related plant problems
Sources
- Oregon State University Extension: Heat wave in the garden: How to identify and prevent heat stress in plants
- Oregon State University Extension: How to protect yourself and your plants during extreme heat
- Texas A&M AgriLife Extension: Texas Vegetable Growers' Handbook, Chapter IV: Cultural Practices
- Clemson HGIC: Why Did My Tomatoes Stop Producing Fruit?
General guidance, not a diagnosis. Written by PlantWiz in our own words from the sources above.