Campanula persicifolia Blue Bells
Grown for the long spikes of open, bell-shaped flowers it sends up through early summer, Campanula persicifolia Blue Bell is one of the more straightforward perennials in a border. The blue bells face outwards along wiry stems, held well above a flat rosette of narrow evergreen leaves. The season runs November to January, and more stems keep coming where spent ones are taken off.
This is a bellflower for the middle of a mixed planting, set in threes so the spikes read together. It goes well with roses, cranesbills and grasses, and the blue sits cool beside soft yellows and creams. Cottage schemes suit it, as does a large pot on a courtyard where the flowers can be seen at close range.
Give it full sun to part shade and free-draining soil. It grows reliably across most of New Zealand. Campanula copes with light shade better than most early summer perennials, which makes it useful on the shaded side of a house. Improve thin or new-build ground with compost and mulch in spring. Set plants 30 cm apart. Check young rosettes for slugs.
Stems carry the flowers to 0.6 to 0.9 m, out of a rosette around 0.3 m wide that persists through winter.
Trimming: Once the last spike has finished, cut the flowering stems down to the basal rosette and leave the evergreen leaves in place. Plants often push a second, shorter flush in February where they are growing strongly. Divide clumps in early autumn every third or fourth season to keep them vigorous.
Deadheading: Work through the clump every week or so during flowering, removing finished spikes at the base. This is the single thing that most extends the display, because the plant redirects energy into new stems rather than setting seed.
Fertilising: One application of balanced slow-release fertiliser in early spring covers the whole season. Keep nitrogen moderate so the stems stay firm enough to hold the flowers upright without staking. Mulch with compost at the same time.
Watering: Steady moisture while the flower stems extend in late spring makes the difference to spike length. Water deeply in dry spells rather than sprinkling, and mulch to keep the root zone cool. Established plants tolerate short dry periods once flowering is over.
Pest Control: Snails and slugs graze the overwintering rosette and the first spring shoots, so control them from late winter. Aphids sometimes build up on flower stems in warm weather and are dislodged with a jet of water.
Disease Management: Powdery mildew and rust both show up in still, humid conditions. Give plants room, water at ground level, and take off affected leaves as you see them. Wet winter soil causes crown rot, so plant on ground that drains freely.
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