GreenlyHeat stress: how to recognise and treat it
Growing conditions
Symptoms
- Leaves wilt in the hottest part of the day and recover in the evening and early morning.
- Flowers and young fruit drop — common in peppers, squash and cucumbers; tomatoes abort flowers after several days above about 29 °C by day or 21 °C at night.
- Brown scorched patches on leaves, and sunscald on fruit, mainly on the sunny side of the plant.
- Cool-season crops such as lettuce, spinach, cilantro and broccoli bolt to flower early.
Organic treatment
- Water deeply rather than often; water wilted plants as soon as you can, otherwise in the morning.
- Mulch to keep the soil cool and moist.
- Shade plants with shade cloth (about 30% shade is enough for most vegetables) and move containers into shade.
- Hold off feeding and pest sprays until it is cooler — many products damage plants when temperatures stay above about 27 °C.
Chemical treatment
Reference information, not a guarantee. Read and follow the label of any product: dose, safety and the days to wait before harvest.
Prevention
- Grow heat-tolerant crops and heat-tolerant varieties of heat-sensitive crops.
- Add compost to sandy soil so it holds water longer.
- When a heat wave is forecast, set up shade in advance and harvest cool-season crops before it arrives.
- Keep weeding through hot spells — weeds compete for water.
Sources
Figures checked against these sources.