Why Are My Pelargonium Leaves Curling?

Overwatering and root rot

Pelargonium originates from the dry, Mediterranean-climate regions of South Africa and is among the most drought-tolerant of all common UK bedding plants. It is far more likely to be killed by overwatering than by drought. When grown in containers that are kept persistently moist, or in heavy, moisture-retentive compost, the roots suffocate and rot. A plant with rotting roots cannot take up water, so despite the compost being wet, the leaves curl, wilt, and turn yellow as though the plant is thirsty.

The classic scenario is a pelargonium watered on a fixed schedule regardless of weather: in a cool, cloudy UK summer, the compost may never dry out adequately between waterings, and root rot can set in within a few weeks.

What to do

• Allow the compost to become almost completely dry between waterings. Pelargonium actively benefits from a dry period between each watering.
• Use a free-draining, gritty compost. A mix of multipurpose compost and perlite in a ratio of roughly three to one is ideal for container pelargoniums.
• Ensure containers have generous drainage holes and never leave the plant sitting in a waterlogged saucer.
• If root rot is already established, remove the plant from its pot, trim away all soft, dark, and mushy root material, dust the cut surfaces with sulphur powder or cinnamon, allow to dry for several hours, and replant in fresh, gritty compost.

Vine weevil

Vine weevil is a devastating pest of container-grown pelargoniums and one of the most common reasons for a sudden, unexplained collapse in late summer or autumn. The adult beetles notch the leaf edges in a distinctive scalloped pattern through the summer, but the damage from the plump, cream-coloured grubs that hatch in the compost is far more serious. The grubs feed on the roots and stems below compost level, progressively destroying the plant's ability to take up water. The leaves curl, wilt, and yellow while the compost feels adequately moist, because the root system has been destroyed.

What to do

• If collapse is sudden and the compost is moist, remove the plant from its pot and examine the roots. The presence of C-shaped cream grubs confirms vine weevil.
• Remove all grubs by hand and dispose of the compost. Replant the salvageable stem and root material in fresh compost.
• Apply a biological nematode control (Steinernema kraussei) watered into the compost in late summer, when soil temperature is above 5 degrees Celsius, to kill grubs before they cause serious damage.
• Check for adult vine weevil beetles at night in late spring and summer: they feed after dark on the leaf edges and can be picked off by torchlight.

Drought and heat stress

While pelargonium is drought tolerant, it will eventually show stress when left too long without water, particularly in small containers in hot weather. The leaf edges begin to curl upward along their length, a response that reduces leaf surface area and limits water loss. This is the plant's first drought-stress signal and generally precedes more serious symptoms such as yellowing and leaf drop. Pelargonium in hanging baskets or terracotta pots dry out particularly quickly.

What to do

• When the leaves curl upward and the compost is dry, water thoroughly and the leaves will usually flatten out within a few hours.
• Although pelargonium benefits from drying out between waterings, it should not be left to the point where the leaves begin to shrivel or the older leaves start to drop.
• Moving pots out of full midday sun during a prolonged heatwave reduces heat stress and water demand significantly.

Oedema

Oedema is a physiological condition that causes pelargonium leaves to develop small, raised, corky bumps on the underside and may be accompanied by slight curling or puckering of the affected leaves. It occurs when the plant takes up water faster than it can transpire it, often during warm, wet periods or after a period of drought followed by generous watering. The condition looks alarming but is not a disease and will not spread.

What to do

• Reduce watering frequency and improve air circulation around the plant.
• Avoid overwatering after a dry spell. Water the plant at the base rather than from above.
• Affected leaves will not recover their appearance but new healthy growth will replace them. Remove damaged leaves if they are unsightly.

Other pests

Aphids, caterpillars, and whitefly occasionally attack pelargoniums and can cause leaf curling alongside other damage. Caterpillars eat ragged holes in the leaves and their frass (droppings) may be visible on the leaves and compost surface. Whitefly cluster on the undersides of the lower leaves. Aphids are most commonly found on shoot tips, causing distortion and curling of the young growth.

What to do

• Inspect the plant carefully, checking the undersides of leaves and within curled growth for pest colonies.
• Pick off caterpillars by hand. Treat aphids and whitefly with insecticidal soap spray, repeating every four to five days for two to three weeks.
• Yellow sticky traps catch adult whitefly and provide early warning of an infestation building.

Frequently asked questions

Why are my pelargonium leaves curling?

Pelargonium leaves curl most often from overwatering and root rot or from vine weevil larval damage. Pelargoniums are adapted to dry conditions and are very susceptible to root rot in persistently wet compost. Vine weevil grubs eat the roots in late summer and autumn, causing the plant to wilt and leaves to curl even when the compost is moist.

Why are pelargonium leaves curling upward?

Pelargonium leaves that curl upward along their edges are typically showing a response to heat or drought stress. The plant rolls the leaf edges to reduce the surface area exposed to strong sun and lower water loss. Move the plant to a slightly less exposed position and ensure it is watered before the compost becomes bone dry.

Why are pelargonium leaves curling and going yellow?

Yellow curling leaves almost always indicate overwatering or root rot in pelargonium. The plant is highly sensitive to wet compost and will decline rapidly when the roots are waterlogged. Check that the compost is not persistently damp and that the container has adequate drainage holes.

How do I revive a wilting pelargonium?

First check the compost: if it is dry, water thoroughly and the plant should recover within a few hours. If the compost is wet and the plant is still wilting, suspect root rot or vine weevil. Remove the plant from its pot, inspect the roots, trim away any rotted material, and replant in fresh, gritty compost.