Centranthus, commonly known as Valerian, is a reliable and long-flowering perennial that brings a relaxed, cottage-garden charm to borders and walls. Flowering over a long period from late spring to mid summer, it produces clouds of small, nectar-rich flowers that are highly attractive to bees and butterflies. Centranthus prefers full sun and well-drained soil, and is particularly tolerant of dry conditions and poor soils, growing happily in gravel or cracks in old walls. Fully hardy and low maintenance, it’s a great choice for informal planting schemes, gravel gardens or coastal areas. Here's how to get your Centranthus off to a good start:

How to plant

— Plant as soon as possible after delivery, ideally within a week. Centranthus is supplied as a 9cm root ball plant, like a potted plant with soil on the roots. It will need watering straight away after delivery and to be positioned in a bright place.

— Root ball plants can often be planted directly into a clear space in well prepared borders. Avoid planting them directly into a space which could become over-crowded by more established plants or directly into challengling growing conditions. Where growing conditions are more challenging, e.g. poor soil, dry areas or areas where there will be competition with other plants, root ball plants should be potted up and grown on in temporary pots in a sheltered spot outdoors until they are more established. They can be transplanted to borders once they have grown a stronger root system. It is important not to transplant them too soon - when they are ready to be transferred, the plant should should come out of the pot with the compost held intact by the roots.

— Plant bare roots or root balls so that the root system is fully submerged in the soil, leaving the top growth exposed above the soil surface. If planting root ball plants directly into a clear border, choose a sunny position with free-draining soil and space the plants 30-40cm apart. Add multipurpose compost to each planting hole to help the new roots grow. If you are planting in containers to grow-on first, you should use multipurpose compost and a 15-20cm pot for each plant.

— Water-in after planting and continue to water regularly whenever to soil feels dry 3-5cm below the surface. Keep hydrated wduring the spring and summer growing seasons, particularly during the first year. Once established they will rarely require warering.

— When planting or transferring into the garden, choose a position in full sun with well-drained soil, they should tolerate most light soils, including sandy or stony soils. Once established, Centranthus tolerates sunny, dry conditons very well.

— Centranthus are fully hardy perennials. There is no need to protect them from frost over winter, although newly-potted plants may need some cover during cold snaps in the first winter.

Aftercare:

— Valerian usually takes 2-3 years to form a full clump. It may produce some flowers in the first year but generally flowers from the second year onwards.

— When planting in autumn, they may produce some initial growth and then become dormant and stop making progress through winter - they will resume growing the following spring. Flowers appear from late spring through to summer.

— After flowering, lightly trim back spent blooms to encourage a second flush of flowering and to maintain a tidy shape.

— Centranthus is a herbaceous perennial and will die back in autumn. Cut back old stems to around 15cm in autumn or winter. New growth emerges from the base in spring.

— Space plants around 30–40cm apart. Over time, Centranthus will form bushy clumps that can be divided in early autumn or spring if needed.

— Prefers well-drained soil in full sun to light shade. Avoid waterlogged conditions, especially in winter.