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Environmental stressLeavesFlowersWhole plant

Heat stress

The response of a plant whose water loss has outrun what its roots can supply: wilting through the hottest part of the day, flower and fruit drop, and stalled growth. A plant that wilts at midday and recovers by evening is showing heat stress rather than drought, and watering it at midday does not address the cause.

What brings it on

Sustained high temperatures, particularly under glass and in containers, where root volume is limited and the compost heats up. Still air makes it worse.

source

Sourced guidancemoderate confidence

  • Royal Horticultural Society: Heat and drought stress

Checked 2026-08-13

Usually seen: June, July, August

Preventing it

Ordered by how much difference each measure actually makes, not by how often it is repeated.

  • Ventilate and shade greenhouses in hot spells, and move vulnerable containers into afternoon shade. Mulching keeps root temperatures down as well as conserving moisture.
    source

    Sourced guidancehigh confidence

    • Royal Horticultural Society: Greenhouse management

    Checked 2026-08-13

Dealing with it once it is there

  • Water thoroughly in the early morning or evening rather than at midday, and shade the plant during the hottest hours. Recovery by evening without watering confirms heat rather than drought.
    source

    Sourced guidancemoderate confidence

    • Royal Horticultural Society: Heat and drought stress

    Checked 2026-08-13

Signs that lead here

Each of these lists the other things that produce the same sign, and how to tell them apart.

On sprays and treatments

GrowingHQ does not tell anyone what to apply, at what rate, or how often. Pesticide approvals differ by country, change without notice, and the product label is legally binding — it is also the document you are holding. What is described here is cultural and physical control, which is what a home grower can act on without a label in front of them.

Plant-specific guides

Where this is one of several causes that look alike on a particular plant, GrowingHQ publishes the differential rather than the general answer.