Hardy perennials tolerate freezing well – provided they stay frozen all winter long. It’s actually the cycle of freezing and thawing that damages most perennials, rather than the sheer cold. Your task is to provide your perennials by insulating them with mulch that allows your plants to gradually slow down in autumn and gradually start growing again in spring.

Winter’s chilling temperatures are accompanied by soil freezing-and-thawing cycles that can disrupt and damage perennial plant roots. A thick layer of mulch placed over and around the plants will insulate the soil and help protect roots from harm.

Photo Credit: ©2001 Dolezal Publishing/Donna Krischan

Winter care actually starts in midsummer. Summer is the last time for feeding plants with nitrogen, since nitrogen promotes growth of new leaves and shoots that will be hard hit by frost. In autumn, before the first frost, apply a new layer of organic mulch, 2-3 inches thick. This will insulate the soil so it retains late-season heat when roots are still active and help it stay cool in spring, so plants will remain dormant until the weather has warmed up. (Remove the mulch gradually in spring when danger of frost has passed.)

After plants experience the first hard frost of the season, cut their stems to 8-10 inches long, adding these clippings to your compost pile. You may want to leave the interesting seed heads of decorative grasses and other plants, especially if the ground will be covered with snow. (Hungry winter birds will be especially grateful.)

In areas that experience combined cold temperatures and limited snow cover, give perennials a single-layer, protective covering of organic mulch such as weed-free straw, pine needles, chipped wood or evergreen boughs. Cover the mulch with plastic net and weight it for wind protection. This covering protects the planting area from icy winds and keeps the ground frozen through cycles of freezing and thawing that otherwise might push unprotected plants out of the soil.

Most damage comes from autumn and spring frosts, when plants are growing. Be prepared to protect your perennials from frost with fabric or plastic floating row covers, cotton bedsheets or even cardboard boxes. It’s important that these covers don’t contact the foliage of your perennials; support them on stakes or poles stretched across the planting bed.

Even areas with mild climates experience the occasional frost. Warning signs to recognize are cold, cloudless nights with little wind and temperatures below 45 degrees F at 10 p.m. That’s when you should lay on protection. An antitranspirant spray, available at nurseries and garden centers, will also provide a few degrees of frost insulation protection.

To care for badly frosted plants, wait until new growth sprouts – or well into spring – to prune damaged stems.

The following pictures and captions demonstrate the easy steps to take in protecting inground perennials during winter.