Crambe, whether the towering Crambe cordifolia with its cloud of tiny white flowers or the edible sea kale (Crambe maritima), is a spectacular border plant with very large, wrinkled leaves. Because crambe is a member of the brassica family, it faces some of the same problems as cabbages and cauliflowers, including club root and flea beetle. Drought, mealy aphids, powdery mildew, and root rot round out the causes of leaf curling, each with distinctive signs to look for.
1. Club root
Club root (Plasmodiophora brassicae) is the most serious disease risk for crambe and the most important to diagnose correctly. The soil-borne pathogen infects the roots of all brassica-family plants and causes them to form swollen, distorted clubs and galls instead of normal healthy roots. The infected root system cannot supply water or nutrients efficiently, and the leaves above ground respond by wilting, yellowing, and curling as if suffering from drought, even when the soil is moist. Club root spores can persist in the soil for 20 years or more.
What to look for
- Leaves wilting, curling, and yellowing despite moist soil
- Roots forming distorted swollen lumps or clubs when the plant is lifted
- Foul smell from the infected root tissue
- History of club root in brassica vegetables in the same area
- Symptoms worsening progressively through the season
How to fix it
There is no cure for club root once a plant is infected. Remove and destroy the infected plant immediately, including as much root material as possible. Do not compost infected plants: bin them or burn them. Lime the soil heavily to raise the pH to 7.0 to 7.5, which inhibits but does not eliminate the pathogen. Do not plant crambe or any other brassica-family plant in the affected area for as many years as possible. In severe cases, replacing the top 20 to 30 cm of soil provides some relief. Starting plants in large containers of fresh compost and planting out mature specimens gives them a better chance of establishing before club root spores reach the roots.
2. Flea beetle
Flea beetles are small, shiny jumping beetles that chew numerous tiny circular holes through the leaves of brassica-family plants, including crambe. The surrounding tissue dies and the leaf curls or puckers around each hole as it dries and shrinks. A heavy infestation on young plants or on soft new spring growth can be severe enough to check growth significantly. Adult beetles overwinter in the soil and emerge in spring to target the first tender emerging leaves.
What to look for
- Many tiny circular holes scattered irregularly across the leaf surface
- Tissue curling or puckering around each hole
- Small shiny beetles visible on the leaves that jump when disturbed
- Damage worst on young plants and new spring growth
- Symptoms intensifying in warm, dry conditions
How to fix it
Cover young plants with a fine insect mesh immediately after planting to exclude adult beetles before they can lay eggs or begin feeding. Keep the soil moist around young plants: flea beetle damage is worse in dry conditions and well-watered plants outgrow the damage more quickly. Sticky traps placed near the plants capture adult beetles. Established crambe with a large root system tolerates significant flea beetle damage without serious setback. For severe infestations on young plants, a pyrethrin-based spray applied in the evening when beetles are less active reduces populations.
3. Drought stress
Crambe cordifolia develops a very extensive deep root system once established and is then remarkably drought-tolerant, but young plants and those recently divided are vulnerable during dry spells. Sea kale (Crambe maritima), adapted to coastal shingle, handles drought even better once established. The huge wrinkled leaves of C. cordifolia lose water rapidly in hot conditions and the plant will curl its leaves inward if the root system cannot keep up with the demand.
What to look for
- Leaves curling inward, especially on young or newly planted specimens
- Soil dry below the surface near the root zone
- Symptoms developing during hot or windy weather
- Established plants less affected than new plantings
- Recovery after deep watering
How to fix it
Water young and newly divided crambe deeply every week during dry spells in the first two seasons. Deep watering encourages the root system to grow down into the soil rather than remaining near the surface. Apply a thick mulch of bark chip or gravel over the root zone to retain moisture. Once established, crambe rarely needs supplementary watering except in extreme drought. Planting in autumn rather than spring gives the root system time to develop before the following summer's heat.
4. Mealy cabbage aphid
The mealy cabbage aphid (Brevicoryne brassicae) is a grey-green aphid covered in a white waxy powder that targets brassica-family plants including crambe. It forms dense colonies on the undersides of leaves and at growing tips, feeding on sap and causing the leaf tissue to curl, yellow, and pucker around the infestation. The distinctive grey mealy appearance of the colony distinguishes it from other aphid species. Heavy infestations can severely weaken crambe plants, particularly in their first season.
What to look for
- Dense colonies of grey-green, powdery-coated aphids on leaf undersides
- Leaves curling downward around infested areas
- Yellow patches on the upper surface above colonies
- Sticky honeydew and sooty mould on stems and lower leaves
- Colony visible from above as a grey powdery patch on the leaf
How to fix it
Apply insecticidal soap or a jet of water directly to the colony on the leaf underside, repeating every few days until populations collapse. The waxy coating on mealy aphids makes them more resistant to some sprays than soft-bodied aphids, so thorough coverage of the colony is important. Parasitic wasps (Diaeretiella rapae) are effective natural predators specifically of brassica aphids. Avoid broad-spectrum insecticides that would also eliminate these beneficial parasitoids. Where infestations are very heavy on young plants, insect mesh helps reduce the population until the plant is established enough to tolerate attack.
5. Powdery mildew
Powdery mildew can infect crambe leaves in warm dry conditions, covering them with a white powdery coating and causing the margins to curl upward. On the deeply textured leaves of Crambe cordifolia the coating can be difficult to see clearly but the marginal curling and general tatty appearance are distinctive. Mildew on crambe is generally less severe than on some other garden perennials but can reduce the ornamental value of the plant if allowed to spread unchecked.
What to look for
- White or pale grey powdery coating on the leaf surface
- Leaf margins curling upward around the infected tissue
- Leaves looking distorted or smaller than normal
- Worst in warm dry spells with poor air circulation
- Symptoms from early summer onward
How to fix it
Remove and bin badly infected leaves. After flowering, cut the plant back to encourage fresh growth. Water at the base in the morning only and avoid overhead irrigation. Improve air circulation around the plant by removing crowding neighbours. A potassium bicarbonate spray applied to unaffected leaves provides some protection against further spread. Crambe plants growing in full sun with good airflow rarely develop severe mildew problems.
6. Root rot
Crambe grows best in deep, well-drained soil and resents waterlogging. In heavy clay or low-lying ground that stays wet over winter, the large fleshy roots are prone to rotting. The plant loses the ability to draw up water and nutrients and the leaves curl and wilt even in wet conditions. The symptoms look identical to drought stress, and checking the roots is the only way to distinguish the two causes.
What to look for
- Leaves curling and wilting despite wet soil
- Roots soft, brown, and foul-smelling when lifted
- Problem appearing after prolonged wet weather or in heavy clay soil
- Crown discoloured or soft at the base
- Club root excluded by checking root shape (club root forms lumps; rot softens roots)
How to fix it
Lift the plant and trim away every rotted root to healthy firm tissue. Dust cut surfaces with sulphur and allow the roots to dry before replanting in improved, well-drained soil. Raise the bed level and incorporate generous amounts of coarse grit and organic matter into heavy clay. Crambe grows best in deep, sandy or loamy soil with excellent drainage. In gardens with persistently wet conditions, grow crambe in a large raised bed or deep container with drainage holes and a gritty compost mix.
Quick diagnosis checklist
| What you see | Most likely cause | First action |
|---|---|---|
| Wilting despite moist soil, swollen distorted roots | Club root | Remove and destroy the plant, lime the soil |
| Many tiny holes, tissue curling around them, jumping beetles | Flea beetle | Insect mesh, keep soil moist, pyrethrin if severe |
| Leaves curl inward, soil dry, young plant | Drought | Deep water, thick mulch, weekly watering |
| Grey powdery aphids on leaf underside, leaves cupping | Mealy cabbage aphid | Insecticidal soap to undersides, repeat applications |
| White powder on leaves, margins curling up | Powdery mildew | Remove affected leaves, cut back, improve airflow |
| Wilting despite wet soil, soft brown roots (no lumps) | Root rot | Lift, prune roots, replant in well-drained soil |
Frequently asked questions
Why are my crambe leaves curling and yellowing?
Crambe leaves curling and yellowing together often indicate club root, a soil-borne disease that affects all brassica-family plants including crambe. Club root distorts the roots into swollen lumps that cannot supply water or nutrients normally, causing the leaves to curl, yellow, and wilt. Lift the plant and check the roots for characteristic club-shaped swellings to confirm the diagnosis.
What are the tiny holes in my crambe leaves?
Tiny round holes scattered across crambe leaves are almost certainly made by flea beetles, small jumping beetles that chew through the leaf surface. The surrounding tissue puckers and curls around each hole as it dies. Flea beetles are most active in warm dry conditions. Row covers, sticky traps, and keeping the soil moist around the plant all help reduce flea beetle damage.
Does crambe get club root?
Yes. Crambe is a member of the brassica family and is susceptible to club root (Plasmodiophora brassicae), the same soil disease that affects cabbages, cauliflowers, and other brassicas. The disease lives in the soil for up to 20 years and causes the roots to form swollen distorted lumps. There is no cure once a plant is infected. Lime the soil to raise the pH above 7, which inhibits the pathogen, and avoid growing crambe or any other brassica in the affected area for as long as possible.
Why are my crambe leaves curling in dry weather?
Crambe cordifolia develops a very large root system over time and once established tolerates dry conditions reasonably well, but young plants and newly divided specimens can curl their leaves during extended dry spells. Deep watering at planting and through the first season, combined with a thick mulch, establishes the deep root system that makes mature crambe drought-resilient.