Cold damage
Blackened, translucent or limp tissue appearing suddenly after a cold night or a spell beside a draught. Tender plants show it well above freezing — basil blackens around 10 °C — so 'there has been no frost' does not rule it out.
What brings it on
A frost, a cold night on a windowsill behind drawn curtains, a draught from a door or an unsealed window, or cold water on a plant that wants warmth. Chilling injury in tender species occurs at temperatures well above freezing.
source
Sourced guidancehigh confidence
- Royal Horticultural Society: Frost damage
Checked 2026-08-13
Preventing it
Ordered by how much difference each measure actually makes, not by how often it is repeated.
- Move tender plants off windowsills on cold nights, particularly where curtains are drawn across them — the space between glass and curtain gets far colder than the room.
source
Sourced guidancemoderate confidence
- Royal Horticultural Society: Protecting plants from frost
Checked 2026-08-13
Dealing with it once it is there
- Leave damaged growth in place until the risk of further cold has passed, then cut back to healthy tissue. The dead material gives some protection to what is beneath it, and cutting immediately exposes undamaged buds to the next cold night.
source
Sourced guidancehigh confidence
- Royal Horticultural Society: Frost damage
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.
- Aglaonema: lower leaves turning yellow
- Apple: flowers dropping without setting fruit
- Apricot: flowers dropping without setting fruit
- Basil: dark or black spots on leaves
- Basil: plant wilting although the soil is moist
- Bay: lower leaves turning yellow
- Calathea: lower leaves turning yellow
- Camellia: flowers dropping without setting fruit
- Chard: plant running up to flower before it is ready to eat
- Cherry: flowers dropping without setting fruit
- Christmas cactus: sudden leaf drop
- Cucumber: plant wilting although the soil is moist
- Lemongrass: brown, crisp leaf tips
- Magnolia: flowers dropping without setting fruit
- Melon: flowers dropping without setting fruit
- Onion: plant running up to flower before it is ready to eat
- Pak choi: plant running up to flower before it is ready to eat
- Plum: flowers dropping without setting fruit
- Rosemary: plant wilting although the soil is moist
- Rubber plant: sudden leaf drop