Lesson 4
Common problems
Powdery mildew is the classic aster complaint, especially in dry summers. Choose resistant varieties (Symphyotrichum 'Little Carlow', S. 'Calliope', A. × frikartii) and water roots not leaves. Mulch in spring to keep the roots cool.
Aster wilt fungus causes whole stems to collapse from the base. Lift and bin affected plants (NOT in the compost); don't replant asters in the same spot for 2 years.
Aphids cluster on bud tips in dry weather — encourage ladybirds with companion calendula, or blast off with water.
Slugs eat fresh spring growth — copper rings or wool pellets at the base of perennials when they re-emerge in April.
Mildew — when to act, when to relax
- A dusty white film on lower leaves in August: normal in dry years, doesn't kill the plant.
- Lower leaves go grey and crisp: increase mulch and weekly deep watering.
- ENTIRE plant white from top to bottom: spray once with 1:9 milk-water; remove worst leaves.
- Stems collapse from base: aster wilt, NOT mildew — lift and bin, rotate.