How to Grow Tussock Bellflowers in Australia

Tussock bellflower (Campanula carpatica), or Carpathian bellflower, is a low perennial in the bellflower family (Campanulaceae), grown for its upturned cup flowers. Its blue, white or rose pink clumps suit path edges, rockeries and pots, and it is unrelated to native tussock grasses (Poa species). The mistake most gardeners make is burying the dust-fine seed, which needs light to germinate.

Three mistakes that matter

1. Burying the seed. The seed is as fine as dust and needs light to germinate, so seed covered with mix often fails to appear. Press it onto the surface and add no more than a dusting of vermiculite to hold moisture.
2. Planting in wet, heavy soil. The clump will not tolerate soil that stays wet, and its roots and crown rot in waterlogged ground or an overwatered pot. Plant in free-draining soil, a raised bed or a rockery pocket, and water when the surface dries.
3. Giving it the full afternoon heat. Hot sun and dry soil stress the clump, and humid nights that stay above about 21°C shorten its life. In hot inland and northern gardens, plant where afternoon shade falls and mulch to keep the roots cool.

When to plant

Seed germinates at 18 to 24°C, so the warmth of the tray decides when to start. Sow in autumn while the days stay warm, or in spring once a tray on a bright sill or a seedling heat mat holds 18°C. One sowing is enough, because each plant forms a clump that lasts for years. Sow Canterbury bells in autumn, from February in the south to July in the north, for flowers the following spring and summer.

At the cold edge of a window, start trays indoors and plant out after the last frost. At the hot edge, keep trays in bright shade so the surface-sown seed never dries out.

Site, soil and setup

The clump stays in one spot for years, so it needs no yearly rotation; replant divisions into freshly composted soil. For ground that stays soggy after rain, read about waterlogged garden soil.

Container growing

All three tussock bellflower colours, blue, white and single rose pink, stay low and suit pots, troughs and hanging baskets. Give one plant a pot at least 20 cm wide and deep, about 5 L. Canterbury bells is taller and needs a pot at least 30 cm wide. Fill pots with premium potting mix, with about a third perlite added for drainage.

• Watering. Water when the top of the mix feels dry, and empty any saucer after rain. See watering pots through summer.
• Feeding. Give fish and seaweed blend at 25 mL per 9 L every fortnight from spring until flowering ends.
• Position. Morning sun and afternoon shade in hot gardens, full sun where summers are cool.
• Snails. A band of copper tape around the pot keeps snails and slugs off the leaves.

Sowing Seeds

Start tussock bellflower in trays, where the fine seed stays lit, moist and out of reach of snails.

Starting under cover

• Fill a clean tray or punnet with fresh seed raising mix, firm it and water it before sowing.
• Mix the seed with a pinch of dry sand, scatter it thinly and press it onto the surface, as in sowing tiny seeds.
• Leave it uncovered, or add only a dusting of vermiculite, then mist it or water the tray from below.
• Keep the tray at the temperature under When to plant, in bright light out of direct sun, under a clear cover.
• Seedlings appear in 10 to 28 days, most within 2 to 3 weeks. Lift the cover once they do, to let air in.
• Prick out seedlings into 8 cm pots once they can be handled, and grow them on somewhere cool and bright.

Sowing direct

Seed can go straight into a fine, weed-free bed in mild weather after the last frost. The seedlings are tiny, hard to find among weeds and easy prey for snails, so trays are the safer start. Press the seed onto raked soil, keep the surface moist with a fine spray and thin seedlings to 30 cm apart.

Transplanting

Plant out once roots fill the 8 cm pot. Harden seedlings off first (a week or so of gradually longer spells outdoors that toughens soft growth), as in hardening off seedlings. Set each plant at its pot depth, 30 cm apart, and water it in with seaweed solution at 30 mL per 9 L.

Canterbury bells

Canterbury bells is a different species: a biennial that makes a leafy rosette in its first year and flowers in its second. Sow and transplant it the same way, and push in a stake at planting, because the flowering stems grow tall.

Care by growth stage

Even moisture, cool roots and light feeding decide how long a clump lives and flowers. It needs far less feed than annual bedding flowers.

Weeks count from sowing. First flowers usually open 23 to 26 weeks after sowing, so autumn sowings flower the following spring. If growth stalls in poor soil, a light dose of all-purpose controlled release granular (NPK around 14-5-10) scratched in each spring can help.

Cutting Back

Regular deadheading keeps flowers coming for weeks, and a trim after the main flush tidies the clump and stops self-sown seedlings.

• Snip each faded flower off at the base of its stalk every few days while the clump is flowering.
• After the main flush, shear the flowered stems back to the leafy mound.
• If the leaves look tired in summer, cut the clump back to its basal growth; fresh leaves follow.
• Where winter cold kills the leaves, clear them away before growth resumes in spring.
• Divide the clump every 2 to 4 years, in early spring or late summer, as in dividing perennials.
• Pull out Canterbury bells once flowering ends, since the plant usually dies after its second summer.

Companion planting

Tussock bellflower belongs at the front of a border or rockery, beside plants that share its free-draining soil and leave it room.

Grows well with

• Aubretia, which likes the same rockery pockets and wall tops.
• Thyme, a low, sun-loving edging that does not smother the clumps.
• Violas, which suit the same cool, lightly shaded front-of-border spots.
• Vegetable beds, where the flowers draw bees and other pollinators.

Keep apart

• Sunflowers and other tall, dense plants, which shade and crowd the low clump.
• Mint and other fast spreaders, which overrun a slow-spreading clump.
• Lettuce and other soft seedlings, which draw snails and slugs to the same bed.

Harvesting Blooms

Pick tussock bellflower once the cups are fully open.

• Cut in the cool of the morning and stand stems in water straight away.
• Cut each stem at its base, so picking doubles as deadheading.
• Pick Canterbury bells when two or three of the lower bells on a stem are open.
• Carry and store Canterbury bells stems upright, because they bend when laid flat.
• Leave a few flowers on each clump if you want to save seed.

Keep cut flowers in a cool room out of direct sun, and top up the water each day. After flowering, seed capsules turn brown and dry; collect them then and store the seed in a paper envelope somewhere cool and dry. The three colours are one species and can cross, so seed from mixed plantings may not come true.

Use the thin-stemmed tussock bellflower in small table posies, and Canterbury bells as a long-stemmed cut flower.

Common problems

Seeds did not come up. Buried seed (see Three mistakes that matter), a tray that dried out or one kept below 18°C are the usual causes. Read more

Pale, stretched seedlings. Seedlings raised in poor light stretch and flop. Read more

Clump wilts and rots at the base. Root and crown rots take hold in wet, heavy soil, and a badly affected plant seldom recovers, so lift healthy pieces into better drainage. Read more

Flowering stops early. Spent flowers left on the plant, and hot, dry weather, end the flush sooner; deadhead as under Cutting Back.

Fewer flowers and a bare centre. The clump is crowded; divide it as under Cutting Back.

Canterbury bells made only leaves. This is normal in the first year, because the plant is a biennial and flowers in its second.

Pests and diseases

Snails do the most harm, from the seed tray onward, while aphids and mildew are usually minor.

Common garden snail (Cornu aspersum). This introduced snail, found in every state and territory, chews holes in soft leaves and flowers, and slugs do the same. Hunt them at night, sink shallow beer traps into the soil, or ring pots with copper tape. Read more

Foxglove aphid (Aulacorthum solani). This green aphid sucks sap from shoot tips and buds, leaving sticky honeydew. Hose it off, or spray horticultural oil or soapy water, but not in hot weather. Read more

Powdery mildew (Erysiphe species). White powdery patches spread over the leaves, most often in warm, humid weather. Pick off affected leaves and spray 1 part full-cream milk to 10 parts water. Read more

Damping off (Pythium species and Rhizoctonia solani). These soil-borne pathogens rot seedlings at soil level, so they collapse in the tray. Read more

Prevention first

• Sow in fresh seed raising mix in clean trays, and lift the cover once seedlings appear.
• Space plants 30 cm apart and water at soil level in the morning.
• Check shoot tips and leaf undersides each week in warm weather.
• Clear leaf litter and rubbish where snails and slugs hide by day.

Tips

1. Tuck plants into gaps in a dry-stone wall or between pavers, where drainage is sharp and the stones keep the roots cool.
2. Plant the blue, white and rose pink forms in a run along a path edge; they share one height and flowering season.
3. In cold gardens, label each clump in autumn, because it can die back in winter and is easy to dig into by mistake.
4. Label Canterbury bells rosettes in their first year so nobody weeds them out before they flower.