Ornamental Horticulture (OH) Leaflet #4
Hybrid roses so frequently fail to survive winters in Vermont that many gardeners have given up on them. Experience of others has shown that at least limited success is possible. These notes are written for the still-hopeful rose gardener and are not intended as foolproof instructions on how to bring roses through the coming winter.
Rose plants can be killed or injured during winter in any of several different ways. These include:
1. Direct injury to tops or roots from extreme cold
2. Root injury from drying-out as a result of plants being heaved out of the ground by alternate freezing and thawing
3. Rapid variation of temperature caused by warming of stems by strong winter sunshine and then rapid freezing
4. Injury caused by animals such as mice
5. Snow or ice breakage
What can the gardener do to prevent such injury?
Injury from extreme cold can be avoided only by selecting the hardiest varieties available. Unfortunately, most hybrid roses have not been thoroughly evaluated for winter hardiness, so Vermont rose gardeners must be willing to experiment for themselves or rely on the experiences of other rose growers in their area. Generally, polyanthas, floribundas, hybrid perpetuals, shrub roses, and many of the "old-fashioned" roses prove more winter hardy than the hybrid teas and grandifloras. The Meidiland series appears from our trials at the University of Vermont to be hardy to at least USDA zone 5, (USDA hardiness map) and marginal by variety in zone 4. The new English David Austin roses also vary widely by variety, ranging from zones 4 to 6. The Canadian explorer series, bearing names of Canadian explorers such as Champlain and Cabot and Kelsey, are either shrub or climbing roses and mostly live in zone 4. (descriptions of varieties, hardiness)
Many gardeners have found that mounding mulch around individual bushes is the most practical way to overwinter roses in this climate. Erect a frame around the rose bush to hold the mulch in place. Chicken wire, roofing paper, or any other sturdy material can be used. Fill the frame to at least 12 inches deep with a loose, porous mulch such as light soil, peat moss, vermiculite, or straw. Too often a dense soil mound cuts off oxygen supply to the roots and crown, smothering the plants. Oak or beech leaves can also be used, but leaves that tend to mat down when wet, such as maple, willow, and poplar, should be avoided as these too can smother plants. The top of the frame can be covered with opaque (not clear) plastic or burlap to keep the mulch from blowing away if necessary.
Canes of bush roses can be cut back to 18" in late fall to facilitate mulching. In early May, before new growth begins, this deep mulch should be removed. The surest method for overwintering roses is to dig the plants in mid-November and bury them in a trench covered with soil. This should be done in a place where water won't stand in the soil during winter. This treatment is especially useful for tree roses whose height makes covering the upright plants difficult or impractical. Uncover the plants and replant them in early May just before growth would normally start.
Climbing roses can be protected by removing the canes from their supports and laying them on the ground. Use a wire hoop to hold them to the ground. Lay a piece of burlap over the canes to protect them during the spring uncovering operation, then mound soil over the canes. Uncover the canes in early May and fasten to a support.
Winter protection should be applied in late November. If protection is applied too early in the fall, it interferes with the natural development of winter hardness in the plant. Roses that are covered before mid-November may be more susceptible to winter injury than ones left unprotected. Before mulching or mounding, the fall cleanup should be completed, removing all plant debris and diseased parts. Even with these treatments, tip dieback can be pruned back at least to 12 inches next spring and the injured tips will be removed at that time. Don't prune too soon--wait until active growth and shoots are several inches long. What appears to be dead at the beginning may really be alive!
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Issued in furtherance of Cooperative Extension work, Acts of May 8 and June 30, 1914, in cooperation with the United States Department of Agriculture. Lawrence Forcier, Director, UVM Extension System, Burlington, Vermont. University of Vermont Extension System and U.S. Department of Agriculture cooperating, offer education and employment to everyone, without regard to race, color, national origin, sex, religion, age, disability, political beliefs, and marital or familial status.
last reviewed 10/31/96