Purple coneflower (Echinacea purpurea) is a staple of the summer garden and easy to prune. It grows in full sun or partial shade in well-drained soil. In the heat of the summer, the daisy-like petals will hold their rich colour longer if the coneflower gets some light shade. It has a stiff habit and looks best in a naturalised or cottage garden setting with textured plants nearby, such as Caryopteris, Amsonia or ornamental grasses.
Cut the stems to half of their height in late spring to delay flowering by 2 to 3 weeks and keep the plants shorter. This will eliminate the need for staking and keep the plants blooming well into fall.
Deadhead the flowers as they begin to fade in the blooming cycle. Look closely down the length of the stem and you may see small flower buds forming for the next blooming cycle. Cut the stem just above those buds. If you do not see flower buds, cut the stem just above the next leaf node down the stem. If the plants are too tall, this cut can be made lower on the stem to help keep the plant sturdy.
Remove all the stems to the basal growth (the new green growth at ground level) in late fall when all blooming is over. You may want to leave some stems present for winter interest or birds, but be aware that the resulting seedlings can be a nuisance in warm climates.
Early pruning and regular deadheading will keep your Echinacea purpurea looking fresh and blooming off and on until frost. If you have a large area of coneflowers, you can apply different pruning techniques to different sections to maximise blooming. The cultivar "Kim's Knee High" is a popular choice and tops out at 2 1/2 feet tall, unlike the native species that can reach as much 4 feet tall.
Avoid rich soil. Coneflowers prefer lean and well-drained soil or it will get tall and leggy.