As soon as the foliage of the common herbaceous peony turns brown, it can be removed from the plant. Remove the dead material down to the ground level. If the foliage was free of disease, place the plant material in your compost pile. If the foliage is diseased, discard it.
Mulching of herbaceous peonies is necessary only the first winter after planting. Mulch helps prevent alternate freezing and thawing of the soil, which pushes plants out of the soil. This action causes damage to the roots and crowns. After the ground freezes, a few inches of mulch should be applied. Any organic material that does not mat down will work, but leaves should not be used. The mulch should be removed before plant growth begins in the spring.
The less common tree peonies should not be cut back to the ground or pruned in the fall. They have woody stems like deciduous shrubs. The only pruning needed for tree peonies might include an occasional shaping of the tree, removal of branch tips damaged by winter injury, or removal of shoot growth (suckers) below the graft union.
Tree peonies also can be cut back to 8 to 12 inches at times, if necessary, to encourage the formation of new shoots. If they aren't diseased, you can collect the leaves from the plant and place them in your compost pile.
-- The Garden Calendar, a service of the Douglas County Extension Service, was written this week by Extension Director Dennis Bejot. For more information, call the Extension Center at 843-7058 from 8 a.m. to 5 p.m. weekdays.