THEY are among the easiest rock plants to grow from seed and provide heaps of colour, cascading over old stone walls or rocks in all shades of blues, purples and pinks.

The hybrids produce low-growing, showy mats of pretty flowers in spring and grow best in well-drained soil in full sun. Good varieties include Bressingham Pink, a double, and Greencourt Purple, a rich purple. Choose a planting site carefully as it's quite a vigorous growing plant that can swamp slower-growing species.

Things to do this weeK: Make sure that supports for herbaceous perennials are in place Deadhead spring-flowering bulbs Plant summer-flowering bulbs Replenish mulches around the base of trees, shrubs and climbers to keep the soil moist and weed-free Plant new crowns of seakale Transplant autumn-sown onions to their final place, spacing them 30cm (12in) apart Protect seeds, seedlings and crops from frost, using cloches and fleece Continue to sow cut-and-come-again crops under cloches or in the greenhouse, including lettuces, chicories, rocket and oriental greens Put a layer of grit or sharp sand around young plants susceptible to slug and snail damage, including hostas and lupins Prune roses and then apply a general fertiliser.