Why Are My Rocket Leaves Curling?

Flea beetle

Flea beetles (most commonly Phyllotreta nemorum and P. undulata on rocket) are tiny, dark, jumping beetles that chew numerous small, round holes in rocket leaves. The thin, tender leaves of salad rocket are among the most susceptible of any garden crop: heavy attacks reduce the leaves to ragged, shotholed, curled remnants that are neither appetising nor usable in the kitchen. Flea beetles are most active in warm, dry conditions from spring through early autumn, with peak populations typically in May, June, and July. They overwinter in leaf litter and soil around previous brassica crops and emerge as temperatures rise in spring.

What to do

• Cover rocket sowings with fine insect mesh immediately at sowing and keep it in place until harvest. On rocket specifically, insect mesh is the single measure that makes the most difference to crop quality between a flea-beetle-riddled failure and a clean, harvestable crop. The mesh must be sealed at the edges: flea beetles are small enough to exploit any gap.
• Water the soil consistently around the plants: flea beetles are much more active and damaging in dry conditions, and well-watered rocket growing in moist soil suffers significantly less damage.
• Sow autumn rocket in August and September: flea beetle populations decline sharply as temperatures drop, and late-summer sowings under mesh produce the cleanest, most flavourful rocket of the year.
• Sow successionally in small batches every 3 to 4 weeks rather than large single sowings: if one sowing is badly affected before the mesh is in place, the next sowing is only a few weeks behind.

Aphids

Cabbage aphid (Brevicoryne brassicae) and peach-potato aphid (Myzus persicae) both colonise rocket, clustering on the underside of young leaves and at the growing tip. Aphid feeding causes the young leaves to curl inward and pucker, and the sticky honeydew promotes sooty mould. On rocket, which is eaten fresh and raw, aphids penetrating into the leaf clusters are particularly problematic as they are difficult to wash out.

What to do

• Inspect rocket plants weekly for aphid colonies, particularly on the underside of young leaves. Small colonies can be squashed by hand or removed with a jet of water. Insect mesh provides aphid as well as flea beetle protection.
• Cut and replace badly aphid-infested rocket rather than attempting to clean heavily colonised plants: a new sowing under mesh is ready in 3 to 4 weeks, which is less time than it typically takes to clear a severe aphid infestation.

Drought

Rocket wilts and curls rapidly in drought, particularly in hot summer conditions. Drought also intensifies the peppery, bitter glucosinolate compounds in the leaves, making drought-stressed rocket unpleasantly strong-flavoured. Drought significantly speeds up bolting, cutting the harvest window even shorter.

What to do

• Water rocket regularly during dry spells, every 2 to 3 days in hot conditions. Do not allow the soil to dry out: consistent moisture produces the mildest-flavoured, most tender leaves and delays bolting.
• Grow rocket in a position with some afternoon shade in midsummer: full-sun positions dry out faster and promote bolting.

Downy mildew

Downy mildew on rocket (Hyaloperonospora parasitica) produces pale yellow patches on the upper leaf surface with a white-grey downy growth beneath. Affected leaves curl and yellow. It is most common on rocket grown under cover in autumn and winter, where cool, damp, poorly ventilated conditions favour the pathogen.

What to do

• Ensure good ventilation for covered rocket crops. Remove and destroy affected leaves promptly.
• Space rocket plants adequately and do not overcrowd: dense sowing is a major contributor to downy mildew in autumn and winter rocket crops.

Bolting

Rocket is one of the most bolt-prone salad crops in the UK garden, particularly in warm weather and long days. Once it bolts, the leaves become increasingly tough and intensely peppery, and the plant is essentially finished as a salad ingredient. Bolting is triggered by high temperatures, long days, and drought stress.

What to do

• Sow little and often: a new pinch of seeds every 3 to 4 weeks provides a continuous supply of young, mild-flavoured leaves rather than a single glut that bolts all at once.
• Harvest regularly: cut the outer leaves rather than pulling up the whole plant, and harvest frequently to prevent the plant from developing the size and energy reserves needed to bolt.
• Choose wild rocket (Diuca tenuifolia) for summer sowings: it is perennial, regrows reliably after cutting, and is far more bolt-resistant than salad rocket.

Frequently asked questions

Why are my rocket leaves curling?

Rocket leaves curl most often from flea beetle damage or aphid feeding. Flea beetles (Phyllotreta species) chew small, round holes in rocket leaves and the tissue between the holes curls and dies in heavy infestations. Rocket is among the brassica family crops most severely damaged by flea beetles in UK gardens: without insect mesh protection, rocket crops from spring to early autumn are almost certain to suffer significant flea beetle attack. Aphids cause the tender young leaves to curl inward around their feeding sites. Drought also causes rocket leaves to curl and wilt, and speeds up bolting.

Why is my rocket bitter?

Rocket becomes increasingly bitter and peppery as it matures and particularly when it bolts (runs to seed). The peppery, slightly bitter flavour of rocket is due to glucosinolates, the same compounds that give all brassicas their distinctive flavour: these concentrate as the plant ages and become more intense after the plant flowers. To keep rocket mild and tender: harvest young leaves regularly (cut-and-come-again); sow successionally every 3 to 4 weeks for a continuous supply of fresh, young plants; water consistently to prevent drought stress, which intensifies the peppery compounds; and harvest before the plant bolts. Wild rocket (Diuca tenuifolia) has a naturally more intense, peppery flavour than salad rocket (Eruca vesicaria) at all stages.

How do I stop rocket bolting?

Rocket bolts (runs to seed) rapidly in warm temperatures and long days, particularly in summer. Once a rocket plant bolts, the leaves become increasingly tough and bitter, and the edible window is essentially over for that sowing. To delay or prevent bolting: sow little and often rather than in large single sowings (every 3 to 4 weeks from March to September); harvest young leaves regularly to prevent the plant directing energy toward flowering; water consistently to reduce drought stress, which speeds up bolting; and choose wild rocket (Diuca tenuifolia) for summer sowings, as it is significantly more bolt-resistant than salad rocket. The best-quality rocket in the UK comes from spring (March to May) and autumn (August to September) sowings; midsummer sowings bolt rapidly.

What is the difference between salad rocket and wild rocket?

Salad rocket (Eruca vesicaria, also called garden rocket or roquette) is an annual with broader, more lobed, tender leaves and a moderate peppery flavour. It grows quickly (ready in 3 to 4 weeks from sowing as a cut-and-come-again leaf) but bolts readily in warm weather. Wild rocket (Diuca tenuifolia) is a perennial with narrower, more deeply cut, tougher leaves and a much more intense, peppery flavour. It grows more slowly, bolts less readily than salad rocket, and once established comes back year after year from its persistent root system. Salad rocket is better for spring and autumn sowing for mild, tender leaves; wild rocket is better for summer sowing and ongoing harvest.