Why Are My Dimorphotheca Leaves Curling?

Aphid infestation

Aphids are the most common pest on dimorphotheca. They colonise the shoot tips and the undersides of the narrow, toothed leaves, causing the foliage to curl and distort. Green aphids and black bean aphid are both found on African daisy. Heavy infestations on young plants stall flowering and cause significant distortion of the shoot tips. Aphid populations tend to build rapidly in warm, dry conditions.

What to do

• Check the shoot tips and the undersides of the narrow leaves regularly from late spring onwards.
• Spray with insecticidal soap every four to five days for two to three weeks, covering the leaf undersides carefully.
• A jet of water dislodges aphids from the toothed leaves effectively as a first response.
• Encourage natural predators: lacewings, ladybirds, and hoverflies all feed on aphids and are attracted to the daisy flowers.

Overwatering

Overwatering is one of the most common causes of dimorphotheca decline in UK gardens. As a plant from the dry grasslands of South Africa, dimorphotheca is adapted to free-draining, relatively poor soil and is intolerant of persistently wet conditions. In heavy clay, in containers without adequate drainage, or in a wet UK summer, the shallow root system deteriorates rapidly. The narrow leaves yellow and curl, and the whole plant loses vigour and flowering capacity. In a wet summer, overwatering is more likely than drought as a cause of leaf curl.

What to do

• Plant dimorphotheca in the most free-draining soil available. It performs best in light, sandy, or gravelly conditions.
• In containers, use a gritty, free-draining compost and ensure excellent drainage. Raise containers off the ground to allow water to escape freely.
• Reduce watering to a minimum during cool or overcast periods. Established border dimorphotheca rarely needs additional watering during a normal UK summer.
• Do not improve the soil with large amounts of organic matter: dimorphotheca actually performs better in relatively poor, dry conditions than in rich, moist ones.

Drought stress

Although dimorphotheca is substantially more drought tolerant than most bedding annuals, extreme drought in containers or very free-draining soil can still cause the leaves to curl and wilt, particularly during an unusually hot UK summer. Container plants are most at risk as their limited compost volume dries rapidly. Drought stress reduces flowering and can cause established plants to go to seed prematurely.

What to do

• Water container-grown dimorphotheca when the compost has dried to 2 to 3 cm depth. In very hot weather, this may mean watering every two to three days.
• Established border plants are largely self-sufficient in UK conditions but may need occasional watering during prolonged dry spells.
• Mulch around border plants with gravel or grit rather than organic mulch: this maintains drainage while reducing moisture loss from the soil surface.

Cold stress

Cold stress causes dimorphotheca leaves to curl and the plant to stall. As a South African annual, dimorphotheca needs warmth to grow well: consistent cold below 10 degrees Celsius at night causes the leaves to curl, pale, and lose their grey-green colour. Plants put out too early in spring before temperatures are stable may look sickly for weeks. Cold stress also prevents the flowers from opening: dimorphotheca flowers close in cold as well as in low light.

What to do

• Do not plant dimorphotheca outside until temperatures are stable and nighttime frosts have passed, typically late May in most UK areas.
• Harden off for at least ten days to two weeks before planting out.
• Choose the warmest, sunniest, most sheltered position available. Cold-stressed plants usually recover well once temperatures improve.

Powdery mildew

Powdery mildew occasionally affects dimorphotheca in warm, dry or humid conditions later in the season. The narrow leaves develop a white powdery coating and may curl at the margins. Drought-stressed plants in crowded conditions are most susceptible. In the UK, powdery mildew on dimorphotheca is most likely in late summer when conditions become more humid.

What to do

• Space plants at 30 cm apart to improve air circulation between the low, spreading mounds.
• Remove and bin affected leaves. Spray remaining healthy growth with a sulphur-based fungicide at the first signs.
• Ensure plants are not drought-stressed: adequate watering reduces susceptibility to powdery mildew significantly.

Frequently asked questions

Why are my dimorphotheca leaves curling?

Dimorphotheca leaves curl most often from aphid infestation or overwatering. Aphids colonise the shoot tips and the undersides of the narrow, slightly aromatic leaves, causing them to curl and distort. Overwatering in poorly drained soil causes the leaves to yellow and curl as the shallow root system deteriorates, since dimorphotheca is adapted to dry, sunny conditions.

Why won't my dimorphotheca flowers open?

Dimorphotheca flowers close at night and in dull or overcast weather: this is entirely normal behaviour. If the flowers remain closed during the day, the position is likely too shaded or the weather too cloudy. Dimorphotheca requires full sun and warm conditions to open and display its flowers fully. In a dull UK summer, even plants in full sun may have flowers that open only partially.

When should I sow dimorphotheca?

Sow dimorphotheca under glass from March to April at 16 to 18 degrees Celsius, or direct in its final position in May once the soil has warmed. It germinates readily and grows quickly. Direct-sown plants often catch up to those started under glass. Plant out or thin to 30 cm apart in a sunny, well-drained position.

Should I deadhead dimorphotheca?

Yes, regular deadheading extends the flowering season of dimorphotheca considerably. Remove spent flower heads as soon as the petals drop to prevent seed set and redirect the plant's energy into producing new flower buds. Without deadheading, dimorphotheca runs to seed relatively quickly. Well-deadheaded plants continue flowering from late spring through to the first frosts.