Red valerian 'Albus' in August: monthly care

Centranthus ruber 'Albus' benefits from two pruning sessions each year to keep it tidy, encourage repeat flowering, and prevent it becoming too woody at the base. The main prune takes place in March, just as new growth begins to emerge at ground level. Cut back all the previous year's stems to within 5–10 cm of the base, removing the old woody growth entirely. This hard prune rejuvenates the plant, promotes bushy new shoots, and prevents the centre from becoming bare and leggy. Use clean, sharp secateurs or garden shears for the job. The second prune comes in August, immediately after the first main flush of flowers fades. Shear back the spent flower stems by about half their length, cutting just above a set of leaves. This tidies the plant, stops it self-seeding everywhere (unless you want seedlings), and often triggers a second, smaller flush of white blooms in early autumn. If you prefer a more natural look or want to encourage wildlife, you can leave some spent heads for finches, which enjoy the seeds. Centranthus doesn't require complex pruning techniques—it's very forgiving. If you miss the August cut, simply remove any tatty or damaged stems as you notice them. Avoid autumn pruning after September, as the old stems provide some frost protection to the crown over winter. If the plant becomes very woody and sparse after several years despite regular pruning, it's often easier to replace it or allow self-sown seedlings to take over, as Centranthus is relatively short-lived, typically performing well for four to six years.

Once established, Centranthus ruber 'Albus' is a low-maintenance perennial that tolerates neglect and dry conditions remarkably well. Water sparingly—only during prolonged dry spells in summer, and even then, established plants often manage without help. Overwatering or planting in poorly drained soil encourages root rot and reduces flowering, so err on the side of dryness. Feed lightly in April or May with a general-purpose granular fertiliser or a handful of blood, fish and bone scattered around the base. Avoid high-nitrogen feeds, which produce lush foliage at the expense of flowers. On poor, chalky or stony soils, Centranthus actually flowers more profusely with minimal feeding—rich soil can make growth soft and floppy. If your plant is thriving, you can skip feeding altogether. This perennial is fully hardy in zones 5–9 and needs no special winter protection in temperate Europe. The old stems die back naturally, and new shoots emerge from the crown in spring. A gravel mulch year-round helps with drainage and keeps the crown dry, which is more important than warmth. Pests are rarely a problem. Aphids occasionally cluster on young shoots in spring; a strong jet of water or a spray of soapy water usually deals with them. Slugs and snails generally leave the foliage alone. Powdery mildew can appear on leaves in late summer, especially in dry conditions, but it's mostly cosmetic—good air circulation and the August prune help minimise it. Root rot is the main risk, caused by winter wet in heavy soil, so drainage is your priority throughout the year.