Why Are My Rhubarb Leaves Curling or Cupping Inward?

Rhubarb leaves are naturally somewhat cupped or wavy — this is a normal characteristic of large-leaved plants and is not in itself a problem. However, when leaves are curling tightly, rolling downward or showing pronounced cupping that is different from normal, it usually indicates one of a small number of causes that are worth investigating. The most common are drought stress, aphid infestation, or in rarer cases herbicide drift from nearby spraying.

Drought stress

In hot, dry weather, rhubarb leaves cup and roll inward as a mechanism to reduce water loss from the leaf surface. This is more pronounced on younger, actively growing leaves. Check the soil — if the top few centimetres are dry and crumbly, the plant needs water. Deep watering and mulching resolves this quickly; leaves usually unfurl within 24 hours of adequate rainfall or irrigation.

Aphid infestation

Aphid colonies feeding on young rhubarb leaves cause the leaf tissue to distort and curl around the insects, creating a protective pocket. Check the undersides of curled young leaves for clusters of small, soft-bodied insects and their cast skins. Insecticidal soap spray applied to the undersides of affected leaves reduces the population and the curling gradually resolves as new growth develops without infestation.

Herbicide drift

If nearby lawns or paths have been treated with weedkiller (particularly hormone-type herbicides such as 2,4-D or MCPA) and wind has carried spray droplets onto rhubarb leaves, the resulting distortion can cause pronounced leaf curling, twisting and abnormal growth. Herbicide-affected growth cannot be reversed — remove affected leaves and the plant usually grows out of it over several weeks if the source of exposure is not repeated.