Achillea ptarmica 'The Pearl'

An evergreen, clump-forming, herbaceous perennial that grows up to 50cm tall and wide.

Pure white, double pompom flowers in summer contrast with dark green, finely-toothed leaves.

Prefers full sun to partial shade and moist, well-draining soil.

Always choose healthy, well-grown plants and plant after autumn rains. Before planting, ensure the root ball is saturated and remove the planter bag or pot with minimal root disturbance. Trim any broken roots and plant at the same level as in the container. Dig a hole twice the diameter of the root ball and press into the soil once planted. Plant approximately 50cm apart; planting too closely leads to spindly growth, poor flowering and eventual plant decline. In a well-planned border, flowering plants should just touch to create a full effect without overcrowding. Water after planting and make sure the plants don't dry out until established.

Apply an organic mulch annually to benefit soil health, improve moisture retention and suppress weeds. Achillea is best propagated by division every two to three years to maintain vigour. Divide in early winter to allow new plants to establish while the soil remains relatively warm. The plants will then burst into life the following spring. Divide plants by placing two spades back to back in the centre of the lifted plant, then chop down and push outwards. The new plants can then be either replanted in situ or somewhere else. Deadhead throughout the flowering season to encourage further blooming. Delay cutting attractive seed heads to retain seasonal interest.

Space plants well apart to avoid powdery mildew in summer.

Perennial Garden