Once the foliage of herbaceous perennials (plants that die back to the ground each year), have been killed by a hard freeze, their stems can be cut off near ground level. Foliage of diseased plants should be removed and destroyed since dead leaves serve as an excellent overwintering site for fungal spores that will re-infect your garden next year. Make sure plants are well watered, going into the winter months.

Perennials damaged or killed during the winter usually are not injured directly by cold temperatures, but indirectly by frost heaving. Frost heaving occurs when the soil alternately freezes and thaws, resulting in lifting and damage to the dormant crown and root system.

This action can be reduced by a winter mulch, which helps prevent rapidly fluctuating soil temperatures. Any perennials that are not reliably winter hardy should be mulched after the ground freezes, usually in late November. A mulch about three inches thick is best. Evergreen boughs, clean straw, or other loose, coarse materials are good mulches. Materials such as tree leaves or grass clippings may compact too much around the plant, inhibiting water drainage and promoting disease development. All new perennials planted this summer would benefit from an application of mulch. Remove mulch gradually as new growth begins in the spring, usually in early March.