Why Are My Radish Leaves Curling?

Flea beetle

Flea beetles (Phyllotreta species) are the most significant pest of radish in UK gardens. The small, dark, jumping beetles chew numerous small, round to irregular holes in the leaves, and the leaf tissue around the holes curls as it dries. In heavy infestations, entire seedlings can be destroyed by flea beetles before the root has had time to develop. Flea beetles are most active in warm, dry weather and are most damaging to seedlings in the first 2 to 3 weeks after germination. Once the roots begin to swell, the plant is better able to withstand leaf damage.

What to do

• Cover radish sowings with fine insect mesh immediately after sowing and keep it in place until harvest. This is the single most effective flea beetle control measure and eliminates the need for any other intervention.
• Water the soil around the seedlings during dry spells: flea beetles are less active on well-watered plants and in moist soil conditions.
• Sow radishes successionally in small batches every 2 weeks rather than large single sowings, so that any flea beetle damage in one batch does not destroy the entire crop.
• Pyrethrin-based insecticides are available for flea beetle control in UK home gardens: apply in the evening when bees are not foraging and repeat after rain. However, insect mesh is more effective and does not risk harming beneficial insects.

Aphids

Cabbage aphid (Brevicoryne brassicae) and peach-potato aphid (Myzus persicae) both attack radish, colonising the underside of the youngest leaves and the growing tip. Aphid feeding causes the young leaves to curl and pucker around the feeding sites. In heavy infestations, the growing tip is completely distorted. The short growing season of summer radishes means aphid infestations often build faster than natural predators can control them.

What to do

• Inspect radish plants weekly for aphids, particularly on the underside of young leaves. Small colonies can be squashed by hand or removed with a strong jet of water.
• Fine insect mesh, as used for flea beetle control, also provides effective protection against aphids: one measure covers both problems.
• Apply insecticidal soap spray to larger infestations, covering the underside of affected leaves thoroughly and repeating every 5 to 7 days.

Drought

Drought is the most common cause of poor-quality radishes. Radish requires consistently moist soil to grow quickly and produce crisp, mild roots: drought causes the growth to slow, the roots to become pithy and woody in texture, and the pungent compounds to concentrate, making the roots hot and unpleasant to eat. The leaves of drought-stressed radishes wilt and curl inward. Even brief periods of drought during the short growing season can significantly reduce root quality.

What to do

• Water radishes regularly during dry spells: every 2 to 3 days in hot, dry weather. The soil should never be allowed to dry out completely between waterings.
• Sow radishes in soil with plenty of incorporated compost to improve moisture retention, particularly in sandy or stony soils.
• Harvest summer radishes promptly at the correct size: radishes left in the ground too long become pithy and woody regardless of watering.

Downy mildew

Downy mildew on radish (caused by Hyaloperonospora parasitica) produces pale yellow patches on the upper leaf surface with a grey-white downy growth on the underside. Affected leaves curl and yellow. Downy mildew is most common in cool, wet conditions and on densely sown plants with poor air circulation. It is more problematic on autumn and overwintered sowings than on fast-growing summer radishes.

What to do

• Thin summer radish sowings to avoid overcrowding: 3 centimetre spacings are sufficient for most summer varieties.
• Remove and destroy affected leaves. Rotate brassica family crops each year to different beds.

Bolting

Radishes bolt (run to seed) rapidly in hot weather, producing a tall flower stem and rendering the root tough and inedible. Summer radishes are particularly prone to bolting in hot, dry conditions or when sown too thickly and competing for moisture. Midsummer sowings in July can bolt before the root is large enough to harvest in hot summers.

What to do

• Sow summer radishes little and often: a pinch of seeds every 2 weeks produces a succession of quick-maturing roots without creating conditions where plants compete and bolt.
• Water consistently to avoid the stress that triggers bolting in dry conditions.
• Avoid midsummer sowings in hot, exposed positions: spring (March to May) and early autumn (late August to September) sowings produce the highest-quality radishes in the UK.

Frequently asked questions

Why are my radish leaves curling?

Radish leaves curl most often from flea beetle damage, aphid feeding, or drought. Flea beetle adults (Phyllotreta species) chew numerous small, round holes in the leaves, and the leaf tissue between the holes curls as it dries and dies. Aphids colonise the underside of leaves and cause them to curl and pucker around the feeding sites. Drought causes radish leaves to wilt and curl inward, and is particularly damaging as it causes the roots to become pithy and unpleasantly hot in flavour. Radishes mature so quickly that even brief pest or drought stress can reduce the quality of the edible root.

What are the tiny holes in my radish leaves?

Tiny, round holes in radish leaves are almost certainly caused by flea beetles (Phyllotreta species), small, jumping beetles that are extremely common on all brassica family crops including radish, turnip, and rocket. The adult beetles chew small, neat holes in the leaves; the surrounding tissue may curl and die around the holes in heavy infestations. Flea beetles are worst on seedlings and young plants: established plants with their growing energy invested in root production tolerate considerable leaf damage. Flea beetles are most active in warm, dry weather and on plants growing in dry soil. The best cultural control is to keep radish well-watered, sow successionally to avoid large vulnerable seedling flushes, and cover the crop with fine insect mesh.

Why are my radishes small and hot?

Small, pithy, or excessively hot radishes are most often the result of drought or growing too slowly. Radish is one of the fastest-maturing vegetables in the garden (most summer varieties are ready in 4 to 6 weeks from sowing) and achieves the best flavour and texture when grown quickly in consistently moist soil. Drought causes radishes to grow slowly, develop a woody, pithy texture, and concentrate pungent compounds in the root, making them unpleasantly hot. Overwintering or large-root varieties left in the ground too long also become pithy and hollow. Water radishes consistently and harvest summer varieties at the correct size (typically the size of a marble to a golf ball) without delay.

When should I sow radishes in the UK?

Summer radishes can be sown outdoors in the UK from March to late August for a continuous harvest. Sow in short rows every 2 weeks for a succession of crisp, mild radishes rather than a glut. Radishes germinate rapidly (typically 5 to 7 days) and are ready to harvest in 4 to 6 weeks. They do not transplant well and must be sown direct. Winter and mooli radishes (much larger varieties) are sown from late July onward for autumn and winter harvest. Radishes bolt (run to seed) quickly in hot summer weather: midsummer sowings in July and August can be disappointing, but sowings in March to May and September produce the best-quality roots.