June 19, 2018
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Proper protection can help hardy roses survive winter

By Reeser Manley

In my education as a gardener, I had a rose period. It was long ago, but I remember having a penchant for old English shrub roses. I don’t remember ever worrying about winter protection for my roses, but then I lived in coastal South Carolina where, I now realize, there was no winter.

Non-native roses of all types, including hybrid teas, grandifloras and floribundas, can be grown in Maine, provided the gardener focuses on the most winter-hardy varieties. Some climbing roses and many old-fashioned shrub roses are hardy in Maine as well, including the Explorer varieties developed in Canada for superior winter hardiness.

Maine winters can damage even the hardiest of roses in several ways: rapid changes in temperature, root injury from desiccation as a result of plants being heaved by alternate freezing and thawing, gnawing by mice beneath the snow and snow or ice breakage. Often, it is the rapid changes in temperature and the repeated freezing and thawing that do the most damage.

The good news is that all of these problems can be mitigated by proper winter protection.

Winter protection begins by ending nitrogen applications in late August. Nitrogen encourages the growth of new shoots which will be less winter-hardy than the older shoots. If you see any new shoots starting to grow from the base of the plant in September, remove them to prevent freezing damage to the plant.

Many rose growers believe that you can increase the winter hardiness of your roses at least one zone by autumn fertilizing with potash. One formulation of potash, “Sul-Po-Mag”, also contains two other beneficial nutrients, sulfur and magnesium. Potash is also in organic materials such as manure, wood ashes and seaweed.

Stop deadheading your roses (removing spent blossoms) after Oct. 1, and allow them to develop hips (fruits). Fruit development promotes hardening of plants as they go into winter.

Beginning in early September, gradually reduce watering. This will also help initiate the process of hardening. Continue to monitor soil moisture through the fall, watering only as needed to avoid extremely dry soil. Stop all watering when the ground freezes.

Don’t do any pruning during the fall except for removing dead, damaged and diseased canes. Wait until the end of April, at the earliest, to prune your roses for summer growth and flower production.

Winter protection techniques are designed to keep rose plants uniformly frozen through the winter and to prevent the damaging effects of freeze-thaw cycles. Do not start too early.

Wait until a hard killing frost has caused most of the leaves to fall, then clean up all dead leaves and other debris around the base of the roses. This eliminates the overwintering stages of fungal diseases and should result in far fewer disease problems next year. Throw the debris into the trash or fire rather than into the compost pile, where temperatures are not high enough during winter to kill the diseases.

In late October or early November, before winterizing your roses, remove all of the old mulch from around the plants and put down new organic mulch such as composted manure or seaweed. This helps control diseases and jump-start growth in the spring.

In mid-to-late November, a couple weeks before the ground freezes and when the plants are fully hardy, bush roses (climbers will be discussed later) should be mounded with 10-12 inches of well-drained soil around the base of each plant. This soil should come from another location in the garden, not from around the roses. Then cover the mound with another 12-16 inches of mulching material such as leaf mold, straw, pine needles or wood chips, holding the mulch in place with evergreen boughs or chicken-wire fencing. This added mulch will help stabilize soil temperature and reduce heaving. If your garden has resident rodents, you may want to skip the addition of this mulch material as it will provide them with a winter home.

Remove the soil and mulch in April when you feel the worst of winter is over. If an extended period of freezing temperatures looms, you can always replace the mound of soil to protect the sensitive crown.

Climbing roses are best winterized by removing the canes from the fence or trellis, laying them on the ground, and allowing snow cover to protect them from extreme cold. If you cannot count on continuous snow cover during the winter, you can mound soil or mulch over the canes on the ground. The practice of leaving the stems attached to the trellis and covering them with burlap offers only a few degrees of winter protection, at best.

The only roses growing in Marjorie’s garden were planted years ago by a bird, perhaps a thrush sitting on a high branch of the old yellow birch at the edge of the drive. The trunk of this tree is now skirted with a colony of native roses that bear simple summer flowers, each a single whorl of pink petals encircling golden stamens, and bright red autumn hips. I don’t worry about their winter survival.

Send queries to Gardening Questions, P.O. Box 418, Ellsworth 04605, or to rmanley@shead.org. Include name, address and telephone number.

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