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Almost every campanula problem traces back to the same conditions: warm, humid, still air, and soil that stays wet around the crown. Get the site right and most years pass with little trouble. Canterbury bells in particular are fairly untroubled apart from rot in badly drained soil and the odd aphid colony.
Slugs and snails are a spring and wet-weather nuisance on new shoots, aphids build up on soft growth, and mildew and rust tend to show from midsummer on, especially after the main flowering when plants are tired.
| Problem | When to watch | What you see |
|---|---|---|
| Damping off and stem rot | Seedlings; wet autumns and winters | Stems collapse at soil level, rosettes go soft |
| Southern blight | Hot, humid summer weather | White threads and tiny round bodies at the base; sudden wilting |
| Powdery mildew | Midsummer on, in still air | White powdery film on leaves |
| Rust | Humid summer and autumn | Orange or brown pustules under leaves |
| Aphids | Spring and early summer | Clusters on shoot tips and buds; sticky leaves |
| Slugs and snails | Spring and wet spells | Ragged holes and slime trails on young growth |
| Spider mites | Hot, dry spells, pots near walls | Pale speckled leaves, fine webbing |
| Caterpillars | Late spring to summer | Chewed leaves and buds, droppings |
Rots at the base
Damping off takes seedlings in wet, crowded trays; use fresh seed mix, sow thinly and water from below. Older Canterbury bells and perennials can develop stem rot where the soil stays waterlogged, especially over a wet winter. The fix is prevention: raised beds, grit in heavy soil, and never burying the crown.
Southern blight is a fungal rot that strikes in hot, humid weather. Look for fine white growth like cotton at the base of the stems, often with tiny tan to brown round bodies the size of mustard seed, and a plant that wilts suddenly. Dig out the plant with the soil around its base and dispose of it in the trash, not the compost. Do not replant a bellflower in that spot for a few years.
Powdery mildew and rust
Powdery mildew shows as a white dusty film, and rust as orange to brown pustules on the undersides of leaves. Both love crowded plantings and still air, and both are worse on tired plants after flowering. Peach-leaved bellflower is often the first to suffer in muggy summers.
Pick off affected leaves early, and after flowering cut badly marked plants back hard to fresh basal growth. Thin congested clumps, water at the base rather than over the leaves, and do not overfeed. Clear away and dispose of infected foliage in autumn so the fungus has less to overwinter on.
If a fungicide seems necessary, choose one labeled for ornamentals and for the specific disease, and follow the label. Improving spacing and air flow usually does more.
Aphids, mites, caterpillars and slugs
Aphids gather on shoot tips and flower buds. Rub small colonies off by hand or knock them off with a jet of water, and let ladybugs and lacewings do the rest. Avoid lush, overfed growth, which is what aphids seek out. Spider mites turn leaves pale and speckled in hot, dry spells, mostly on pots against warm walls; misting the undersides of the leaves and moving pots to a cooler spot helps.
Caterpillars chew leaves and buds; check the plants in the evening and pick them off. Slugs and snails can strip young shoots, and the low-growing Serbian and trailing bellflowers are especially at risk. Collect them on damp evenings, use traps, or apply an iron phosphate bait around the plants in spring.
Prevention in short
Plant in fast-draining soil, raise beds on clay, keep the crown at soil level, and leave room for air between plants. Give afternoon shade where summers are hot, water at the base, feed lightly, and deadhead and cut back spent stems so tired foliage does not linger.
Divide perennial clumps before they become congested, and remove any plant that collapses from rot rather than trying to nurse it. Healthy, uncrowded bellflowers seldom need anything stronger than a pair of scissors and a watering can.