Plant problems

Why Are My Rudbeckia Leaves Curling?

Q: Is rudbeckia fulgida Goldsturm a perennial?

Yes. Rudbeckia fulgida 'Goldsturm' is a long-lived, reliably hardy herbaceous perennial in UK gardens; it is one of the most dependable, most versatile, and most widely praised UK garden perennials and has been grown in UK gardens for many decades. Hardiness: Rudbeckia fulgida 'Goldsturm' is fully hardy throughout the UK and tolerates temperatures well below the minimum temperatures encountered in even the coldest UK winters; it dies back to a low, ground-hugging rosette of leaves in winter and re-emerges vigorously in spring. Long-term performance: established clumps of R. fulgida 'Goldsturm' improve in performance year on year for the first several years as the clump expands; a well-established, three to five year old clump in a sunny, adequately fertile and moist UK garden border produces very large numbers of flowers and creates a very impressive, long-lasting late summer and autumn display. Division: after several years (typically five to seven years or more), the central portion of the clump may become congested, woody, and less productive; the outer portions of the clump continue to produce vigorous growth and good flowering; dividing the clump in spring (March to April as new growth emerges) by digging it up, dividing it into sections with a sharp spade, and replanting the outer, more vigorous sections while discarding the congested centre refreshes the plant, maintains vigour, and provides additional plants for planting elsewhere in the garden; division is also the simplest and most reliable method of propagating R. fulgida 'Goldsturm'. Deadheading and winter interest: R. fulgida 'Goldsturm' can be deadheaded during the flowering season to extend the duration of the floral display by removing faded flower heads; alternatively, leaving the spent flower heads on the plant through autumn and winter provides very attractive, architectural, dark seed-cone interest in the winter garden, food for seed-eating birds, and habitat for overwintering invertebrates.

Rudbeckia (black-eyed Susan) is a very popular UK garden perennial and annual. The large, rough, dark green leaves curl and turn pale most often from powdery mildew, which is one of the most consistently troublesome diseases of rudbeckia in UK gardens from July to October; from slug and snail damage on the young spring leaves of established perennial clumps; from drought stress; or from aster yellows phytoplasma producing its very distinctive combination of green flowers and distorted growth.

Powdery mildew

One of the most consistently observed problems on rudbeckia in UK gardens; one of the most mildew-prone ornamental plants in UK late summer and autumn. White, fine, powdery coating develops on upper and lower leaf surfaces and stems particularly from late July to October; heavily mildewed leaves turn pale, yellow, curl, and may die prematurely; very disfiguring at exactly the time the plant should be at its most attractive in full flower.

What to do

Space plants adequately (at least 40 to 50 cm for R. fulgida 'Goldsturm') for good air circulation; apply a mulch (7 to 10 cm) in spring to retain soil moisture; water deeply during dry spells from July to September; remove mildewed leaves promptly and dispose of in general waste (not compost); sulphur-based fungicide sprays are approved in the UK for powdery mildew on ornamental plants and are most effective when applied preventatively from the first signs of disease in July or August.

Slugs and snails

The young, soft, tender newly emerging leaves of perennial rudbeckia (particularly R. fulgida 'Goldsturm') in April and May are very attractive to slugs and snails. Irregular holes, ragged edges, and distortion of the young leaf tissue cause the emerging leaves to curl and look misshapen as they expand. Slime trails are typically visible on or near the plant. Heavy slug damage to the emerging spring rosette can significantly stunt early development.

What to do

Check around the base of emerging rudbeckia clumps at dusk and after dark from April to May; collect and dispose of slugs and snails found near the plants; apply iron phosphate slug pellets (approved for use in UK organic gardening systems) around emerging plants; apply Phasmarhabditis hermaphrodita nematodes (biological slug control) to moist soil around emerging plants when soil temperature is above 5°C from April; copper tape around individual container plants provides a physical barrier; once the leaves have hardened and developed a rougher texture the plants are less susceptible to slug damage.

Drought stress

Particularly affects recently planted, not yet well-established plants; the large, rough, slightly hairy leaves lose water relatively rapidly in hot, dry, windy conditions. Established, in-ground plants in UK gardens develop a robust root system making them considerably more drought-tolerant. Even established plants may wilt and show leaf curl in the hottest part of a severe dry UK summer in thin, freely draining soil.

What to do

Water recently planted rudbeckia thoroughly and regularly throughout the first growing season; apply a mulch around the planting to retain soil moisture; established in-ground plants generally tolerate UK drought conditions well once they have developed a full root system; water established plants during prolonged dry spells in July to September if leaf wilting and curling is severe; a well-mulched, adequately moist soil is the best long-term prevention for drought stress in rudbeckia.

Aster yellows

Candidatus Phytoplasma asteris, transmitted by leafhopper insects, affects rudbeckia with the same distinctive symptoms as echinacea: flower petals replaced by small green leafy structures (phyllody), abnormal greening of flowers (virescence), unusual bushy congested shoot proliferation (witches' broom), narrow pale yellowing leaves, and general stunting. There is no cure.

What to do

Remove infected plants from the garden immediately and dispose of in general waste; do not compost infected plant material; the distinctive combination of green flowers, phyllody, witches' broom, and yellowing together is the most reliable diagnostic indicator; single symptoms in isolation are not sufficient to diagnose aster yellows; replace with healthy plants in a different area of the garden.

Frequently asked questions

Why are my rudbeckia leaves curling?

Rudbeckia leaves curl most commonly because of powdery mildew (one of the most consistently troublesome diseases on rudbeckia in UK gardens; white fine powdery coating on leaf surfaces from late July to October; adequate spacing for good air circulation; spring mulch to retain soil moisture; deep watering in dry periods July to September; remove mildewed leaves promptly; sulphur-based fungicide approved in UK for ornamental plants applied preventatively from first signs in July to August), slugs and snails on young spring leaves (soft tender newly emerging leaves in April to May very attractive to slugs and snails; irregular holes ragged edges distortion and curling; check at dusk and collect; iron phosphate slug pellets; Phasmarhabditis hermaphrodita nematodes to moist soil when above 5°C from April; less susceptible once leaves harden), drought stress (particularly recently planted not yet established plants; large rough hairy leaves lose water relatively rapidly; water thoroughly and regularly in first growing season; mulch; established in-ground plants considerably more drought-tolerant), or aster yellows (Candidatus Phytoplasma asteris transmitted by leafhoppers; green flowers phyllody witches' broom pale yellowing leaves and general stunting; no cure; remove and destroy infected plants; do not compost).

How do I prevent powdery mildew on rudbeckia?

Air circulation: good air circulation around plants significantly reduces mildew severity; avoid very enclosed sheltered spots with very little air movement; adequate spacing (at least 40 to 50 cm for R. fulgida 'Goldsturm'); removing overcrowded congested inner stems when dividing and replanting opens up the crown. Soil moisture: mulch (7 to 10 cm) of well-rotted garden compost or composted bark applied in spring; water deeply and regularly during dry spells July to September; consistent soil moisture reduces mildew severity. Removing mildewed foliage: remove and dispose of leaves beginning to show mildew; do not compost mildewed foliage; dispose of in general waste. Chemical control: sulphur-based fungicide sprays approved in the UK for powdery mildew on ornamental plants; apply at first sign of disease in July or August; repeat at intervals stated on product label; primarily preventative rather than curative. Alternatives: Rudbeckia laciniata and R. nitida may show somewhat less severe mildew than R. fulgida 'Goldsturm' in certain conditions.

Is rudbeckia fulgida Goldsturm a perennial?

Yes. Fully hardy herbaceous perennial throughout the UK; tolerates well below UK winter minimum temperatures; dies back to a low ground-hugging rosette in winter and re-emerges vigorously in spring. Performance: established clumps improve year on year for the first several years as the clump expands; a well-established 3 to 5 year old clump produces very large numbers of flowers and a very impressive long-lasting late summer and autumn display. Division: after 5 to 7 or more years the central portion may become congested woody and less productive; divide in spring (March to April as new growth emerges) by digging up and splitting into sections with a sharp spade; replant outer more vigorous sections; discard congested centre; also the simplest reliable method of propagation. Deadheading and winter interest: deadhead during flowering season to extend display; alternatively leave spent flower heads through autumn and winter for attractive dark seed-cone interest, food for seed-eating birds, and habitat for overwintering invertebrates.

How do I grow rudbeckia hirta from seed?

When to sow: indoors in a propagator or on a warm windowsill at 18 to 22°C from late February to April; earlier sowing gives earlier flowering plants; later sowing gives plants flowering from August to October. Sowing method: sow seed thinly on the surface of fine moist peat-free seed compost; cover with very thin layer of fine compost or vermiculite; water gently; cover with a clear propagator lid or polythene; place in a warm propagator or on a warm windowsill at 18 to 22°C; seeds germinate in 10 to 21 days at the right temperature. Pricking out: prick out seedlings when large enough to handle into individual small pots or module cells; grow on in a frost-free greenhouse cold frame or on a bright frost-free windowsill; pot on as the plants grow. Hardening off and planting out: harden off gradually over 1 to 2 weeks before planting out after the last frost date in late May to June. Position and spacing: plant in a sunny position in well-drained reasonably fertile soil; space at 30 to 45 cm; water in well; feed with balanced liquid fertiliser every 2 weeks from June to August.