Astrantia, or masterwort, is one of the most distinctive cottage garden perennials, with deeply lobed palmate leaves and intricate pincushion flowers surrounded by papery bracts in white, pink, or deep wine red. It tolerates a wide range of conditions but performs best in moist, partly shaded positions. When the attractive foliage curls, develops white patches, or shows signs of pest damage, the most likely culprits are powdery mildew and aphids, both of which are extremely common on astrantia and both of which respond well to timely treatment.
1. Powdery mildew
Powdery mildew is the most common problem on astrantia and the primary reason its foliage deteriorates after the first flush of flowers. The fungal pathogen colonizes the upper and sometimes lower surfaces of the deeply lobed leaves, producing a characteristic white to grey powdery coating. Affected leaves curl upward and inward, yellow, and eventually shrivel. Warm, dry days combined with cool, humid nights create ideal conditions. Plants in sheltered borders or in crowded plantings with poor air circulation are most severely affected. The problem is so common on astrantia that experienced gardeners plan for it and cut back preemptively.
What to look for
- White or grey powdery coating on upper leaf surfaces
- Leaves curling upward and inward around infected patches
- Rapid deterioration of foliage in mid to late summer
- Symptoms spreading from the most crowded or sheltered parts of the clump outward
- New basal growth at the crown remaining healthy while upper leaves deteriorate
How to fix it
Cut the entire plant back hard to basal level immediately after the first main flowering flush, typically in early to mid summer. This removes all infected tissue and stimulates a fresh rosette of clean leaves and often a second flowering. Apply a sulfur-based or potassium bicarbonate fungicide every seven to ten days if mildew strikes before flowering is complete. Improve airflow by dividing congested clumps and spacing plants at least 40 cm apart. Do not compost infected material. Ensure consistent soil moisture, as drought-stressed plants are far more susceptible.
2. Aphids
Aphids colonize astrantia stems and the undersides of young leaves in spring and early summer. They are particularly drawn to the soft growth around developing flower stalks and the central crown. Their feeding causes leaves to curl and distort, and the sticky honeydew they produce can foul the intricate bracts of the flowers. Astrantia aphids include the root aphid (Dysaphis apiifolia), which feeds underground on roots, as well as more typical above-ground species.
What to look for
- Curled or twisted leaves on new growth and around developing flower stems
- Clusters of pale green, grey, or cream insects on stems and leaf undersides
- Sticky honeydew on leaves and flower bracts
- Ants foraging on stems
- Plant wilting and showing yellowing despite adequate moisture (root aphid)
How to fix it
Blast above-ground colonies off with a strong jet of water. Apply insecticidal soap or neem oil every three to five days until colonies clear. For suspected root aphid, water a neem oil drench around the root zone. Encourage natural predators by planting companion umbellifers and avoiding broad-spectrum pesticides. Healthy, well-watered astrantia in good airflow is much less attractive to aphids than stressed, crowded plants.
3. Drought stress
Astrantia is native to moist mountain meadows and woodland edges and struggles in prolonged dry conditions, particularly in full sun. The deeply lobed leaves curl inward when the plant cannot replace water lost through transpiration. Drought stress also accelerates post-flowering mildew and reduces the number of secondary flower stems. Container-grown astrantia and plants on free-draining soils are most at risk.
What to look for
- Leaves curling inward, looking dull or slightly bleached
- Soil dry at depth when probed
- Plant failing to produce secondary flower stems after first flush
- Symptoms worst in full sun and on sandy or gravelly soils
- Leaves recovering and flattening after deep watering
How to fix it
Water deeply and consistently at the base of the plant during dry periods. Apply a generous layer of organic mulch to retain moisture and keep roots cool. Astrantia performs far better in partial shade than in full sun on dry soils: if drought stress is recurring, relocate to a shadier, moister position. In cottage garden borders, plant alongside moisture-retaining companions and avoid positioning astrantia near the dripline of walls or fences that create dry shadows.
4. Slugs and snails
Slugs target astrantia's soft basal leaves and developing flower stems, particularly in spring and in moist gardens. They rasp irregular holes in the leaf surface and chew leaf margins, causing the damaged tissue to curl and deteriorate. The deeply cut nature of astrantia leaves means that slug damage can create a confusing pattern of holes between the natural lobes, but close inspection of the margins and the presence of slime trails confirm the diagnosis.
What to look for
- Irregular holes through leaf surfaces, particularly at leaf margins
- Leaf edges curling and shriveling around damage sites
- Silvery slime trails on leaves, stems, and nearby soil
- Damage appearing overnight or after rain
- Young emerging growth in spring most severely targeted
How to fix it
Apply iron phosphate slug pellets around plants from early spring before new leaves fully emerge. Use copper tape around container astrantia. Check nearby mulch and debris at night with a torch. Encourage natural predators including frogs, hedgehogs, and ground beetles. Avoid over-mulching around the crown, as this creates ideal slug shelter at the plant's most vulnerable point.
5. Leaf spot
Fungal leaf spot diseases occasionally affect astrantia in wet seasons, producing dark spots on the lobed leaves. The tissue around each lesion may curl and crisp as cells die. Because astrantia leaves are already deeply divided, the distortion caused by leaf spot can make diagnosis harder, but the consistent presence of dark, water-soaked or dry spots distinguishes it from mechanical damage or pest feeding.
What to look for
- Dark brown or black spots on leaf surfaces
- Pale or yellow halos around lesions on some infections
- Leaf tissue curling and crisping around affected areas
- Infection spreading from lower leaves upward in wet conditions
- Symptoms worst after prolonged wet or humid weather
How to fix it
Remove and dispose of infected leaves. Avoid overhead watering. Apply a copper-based fungicide every ten to fourteen days during active infection. Clear plant debris in autumn as spores overwinter in fallen leaves. In very wet seasons, the post-flowering cut back removes infected material and gives the plant a clean restart.
6. Root rot
Despite preferring moist conditions, astrantia does not tolerate waterlogged or compacted soils where roots become oxygen-deprived. Root rot caused by Phytophthora or Pythium prevents normal water and nutrient uptake, causing leaves to yellow, curl, and collapse despite wet soil. This is more likely in heavy clay gardens or containers without adequate drainage holes.
What to look for
- Leaves yellowing and curling despite moist or wet soil
- Plant wilting progressively and not recovering
- Crown soft or discolored at soil level
- Root system brown and mushy when the plant is lifted
- Whole plant collapsing through wet winters in heavy soils
How to fix it
Improve drainage by adding coarse grit or organic matter to heavy soils. Plant astrantia in raised beds in problem gardens. Ensure container drainage holes are clear. Astrantia needs moisture-retentive but freely draining soil: loamy soil enriched with compost, not compacted clay or peat that becomes waterlogged. Lift affected plants, trim rotted roots, and replant in better-drained conditions.
Quick diagnosis checklist
| Symptom | Most likely cause | First action |
|---|---|---|
| White powder, upward curl after flowering | Powdery mildew | Cut back hard, sulfur fungicide |
| Curled stems, insects, sticky residue | Aphids | Water blast, insecticidal soap |
| Inward curl, dry soil, full sun position | Drought stress | Deep water, mulch, move to part shade |
| Ragged holes, slime trails, overnight damage | Slugs and snails | Iron phosphate pellets, hand pick |
| Dark spots, crisping curl, wet season | Leaf spot | Remove leaves, copper fungicide |
| Yellowing curl, wet soil, crown soft | Root rot | Improve drainage, lift and replant |
Frequently asked questions
Why are my astrantia leaves curling?
Astrantia leaves most often curl because of powdery mildew infection in warm, dry conditions or aphid colonies on new growth. Both are very common on this plant. Check leaf surfaces for white powder and inspect stems and flower stalks for clusters of insects to narrow down the cause.
Does astrantia get powdery mildew?
Yes. Astrantia is very susceptible to powdery mildew, particularly in mid to late summer after the main flowering period. Warm days with cool, humid nights trigger the fungal growth, which creates a white dusty coating on the deeply lobed leaves and causes them to curl. Cutting the plant back after the first flowering flush and improving airflow are the most effective preventative measures.
Can drought cause astrantia leaves to curl?
Yes. Astrantia grows naturally in moist woodland and meadow conditions and does not tolerate prolonged drought. In dry spells, particularly in full sun, the deeply lobed leaves curl inward and the plant may stop producing new flower stems. Water deeply at the base and apply organic mulch to retain soil moisture.
Should I cut astrantia back when leaves are curling?
Yes, cutting astrantia back hard to basal level after the first main flowering flush in early summer is the best way to tackle powdery mildew and stimulate a second flush of clean flowers and foliage. The plant responds vigorously to this treatment and often looks better in late summer after the cut than it did before it.
What causes astrantia leaves to curl in shade?
Astrantia in shade is most susceptible to powdery mildew (from poor airflow), slug damage (creating ragged holes and curled edges), and aphid colonies. It is less likely to suffer from drought in shade than in sun. Inspect the undersides of leaves for insects and check for slime trails near the plant base to identify the culprit.