Why Are My Hesperis Leaves Curling?

Aphid infestation

Aphids are the most common pest on hesperis. Cabbage aphid and black bean aphid both colonise sweet rocket, clustering on the shoot tips, the developing flower stems, and the undersides of the leaves. Aphid feeding causes the leaves to curl, pucker, and distort, and heavy infestations on the developing flower stems can significantly reduce flowering. Because hesperis produces tall, branching flower stems in its second year, aphid colonies can spread rapidly through the plant.

What to do

• Check the shoot tips and the undersides of young leaves regularly from early spring in the second year of growth, when the plant is most attractive to aphids.
• Spray with insecticidal soap every four to five days for two to three weeks, ensuring coverage of the leaf undersides and developing flower stems.
• Encourage natural predators: the flowers of hesperis are valuable for beneficial insects including hoverflies and parasitic wasps.
• A strong jet of water dislodges aphids from the robust leaves and stems effectively as a first step before chemical control.

Flea beetle damage

Flea beetles are a very common and persistent problem on all brassica family plants, and hesperis is no exception. The small, jumping beetles chew numerous small round holes in the leaves, and the damaged tissue curls and shrivels at the edges. Young seedlings and the first-year rosette leaves are most vulnerable to severe damage. Established second-year plants with large, tough leaves are more tolerant, though heavy flea beetle pressure in spring can still affect the appearance and vigour of the developing flower stems.

What to do

• Cover young hesperis seedlings with fine insect-proof mesh immediately after germination to exclude flea beetles through the most vulnerable seedling stage.
• Water the plants regularly: flea beetle damage is significantly worse on drought-stressed plants than on well-watered ones.
• Once the first-year rosette is large and well-established, flea beetle damage is rarely severe enough to warrant further treatment.

Clubroot

Clubroot affects all members of the brassica family including hesperis. Infected plants develop swollen, distorted roots that cause the leaves to wilt, yellow, and curl despite apparently adequate moisture in the soil. The disease is caused by a soil-borne organism that persists in the ground for many years. In gardens with a history of clubroot in brassica crops, hesperis is particularly at risk and may decline rapidly after planting out, even when healthy at the time of transplanting.

What to do

• Pull a declining plant and examine the roots: irregular, club-like swellings are the definitive sign of clubroot infection.
• Remove and bin all infected plants. Do not compost them or dig the roots into the soil.
• Lime the soil to raise pH to 7 or above before sowing or planting: clubroot is significantly less severe in alkaline conditions.
• Avoid growing hesperis or other brassicas in infected soil for as long as possible. Rotate brassica-family plants to a fresh area each year.

Drought stress

Hesperis is tolerant of moderate drought once established but the large, slightly hairy leaves wilt and curl inward in prolonged dry conditions, particularly for young first-year plants in summer. Drought stress reduces the vigour of the plant going into winter and can result in a poorer flowering performance the following spring. In very free-draining soils or in exposed positions, watering through the first summer after sowing is important for establishing strong plants.

What to do

• Water young first-year hesperis plants during dry spells in their first summer of growth to ensure they build up a strong root system before winter.
• Mulch around plants to retain soil moisture and keep the root zone cool through dry summer periods.
• Second-year plants in flower benefit from watering during prolonged dry spells in May and June to extend the flowering season.

Downy mildew

Downy mildew occasionally affects hesperis, particularly in cool, wet conditions in autumn or early spring. Yellow or pale patches develop on the upper surface of the large leaves, and in moist conditions a grey or pale purplish downy growth is visible on the undersides of affected areas. The leaves curl slightly at the margins. It is most damaging on first-year plants during a wet autumn but usually does not kill established plants.

What to do

• Improve air circulation by spacing plants at least 45 cm apart and avoiding overcrowding.
• Remove and bin affected leaves. Avoid overhead watering which promotes the spread of downy mildew spores.
• Spray with a copper-based fungicide according to the label directions at the first sign of infection.

Frequently asked questions

Why are my hesperis leaves curling?

Hesperis leaves curl most often from aphid infestation or flea beetle damage. Aphids cluster on the shoot tips and young leaves, causing them to curl and distort. Flea beetles create numerous small round holes in the leaves of this brassica-family plant, causing the damaged tissue to curl and shrivel at the edges.

Why are my sweet rocket leaves turning yellow?

Yellow leaves on hesperis are usually caused by clubroot infection, nutrient deficiency, or the natural decline of the lower leaves as the biennial or short-lived perennial matures. Pull a plant and check the roots: swollen, distorted roots indicate clubroot. If the roots are healthy, try feeding with a balanced liquid fertiliser and ensure adequate moisture.

How long does hesperis live?

Hesperis matronalis is typically a biennial or short-lived perennial that flowers best in its second year and then declines. In good conditions it may persist for three or four years, but most gardeners treat it as a biennial and maintain the plant by allowing it to self-seed freely. Self-sown plants are usually more vigorous than older plants that are kept going beyond their best season.

When is the best time to enjoy sweet rocket's fragrance?

The common name sweet rocket refers to the remarkable evening fragrance of the flowers, which intensifies strongly after dusk and on warm, still evenings. The scent is faint or absent during the day. Plant hesperis near paths, seating areas, or open windows to enjoy the evening fragrance from May through June.