When to plant Red valerian 'Albus'?

Centranthus ruber 'Albus' thrives in full sun or partial shade and is particularly well suited to free-draining soils. It performs best in sandy, loamy or chalky ground and tolerates poor, alkaline conditions better than most perennials. If your soil is heavy clay, dig in plenty of grit or sharp sand before planting to improve drainage—waterlogged roots are the main cause of failure with this plant. Plant in March, April or May for establishment before summer, or in September and October to give roots time to settle before winter. Space plants 45 cm apart to allow for their mature spread of 40–60 cm. Dig a hole slightly larger than the root ball, set the crown at the same level it was growing in the pot, and backfill with soil mixed with a little compost if your ground is very poor. Firm gently and water in well. After planting, water regularly for the first few weeks until you see new growth, then reduce frequency—Centranthus has low water needs once established and actually prefers drier conditions. A light mulch of gravel or grit around the base helps suppress weeds and keeps the crown well drained, which is especially useful on heavier soils. Avoid organic mulches like bark, which can retain too much moisture. This perennial self-seeds freely, so if you want to control spread, deadhead spent flowers before seed sets. Otherwise, allow a few flower spikes to mature and you'll find seedlings appearing in cracks in paving and gravel—often in the most unlikely spots, which is part of the plant's charm.