Mother Nature Can't Do it for You
Hybrid roses so frequently fail to survive winters in New Hampshire that many gardeners have given up on them. These notes are written for the still-hopeful rose gardener. Although they are not fool-proof, they should help to bring your roses through the coming winter in good shape. Rose plants can be killed or injured during the winter in several different ways. These include: direct injury to tops or roots from extreme cold; root injury from drying-out as a result of plants being heaved out of the ground by alternate freezing and thawing; injury caused by animals such as mice; rapid variation of temperature-caused by warming of stems in strong winter sunshine followed by rapid freezing; and snow or ice breakage.
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 New Hampshire rose gardeners must be willing to experiment for themselves or rely on the experiences of other rose growers in the area. Generally, floribundas, hybrid perpetuals, shrub roses, and many of the "old-fashioned" roses prove more winter hardy than the hybrid teas and grandifloras.
Many gardeners have found that mounding mulch and soil around individual bushes is the most practical way to overwinter roses in this climate. The following procedure should be almost fool-proof. Prune your rose just enough to adjust the size of the plant to its winter covering. Tie the canes together with twine. Erect a cylindrical frame around the rose bush to hold 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 peat moss, vermiculite, pine bark or straw. If you have an especially tender rose you may first want to bring in enough soil to cover just the graft (usually 2-4 inches is sufficient). 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 can smother plants. The top of the frame can be covered with opaque (not clear) plastic or burlap to keep the mulch from blowing if necessary then mound soil to a depth of 10-12" around the base of the frame. If you have small plants you can also use the styrofoam covers sold by garden centers; then mound soil around the outside base of the styrofoam cover.
For climbing roses either of the following procedures can be used. If your roses are growing in a fairly protected area, out of harsh winds and extreme temperatures, wrapping with burlap or evergreen boughs will give sufficient winter protection. After the first hard frost of the fall, secure canes to their support and prune off long ends. Next wrap the canes in burlap, straw or evergreen boughs and tie with twine. Mound 10-12" of soil around base of the plant.
In extremely cold areas where winter damage is common, the best way to protect a climbing rose is to shield the entire plant with earth. After the first hard frost of the fall, detach the plant from its support and tie its canes together. Bend the canes to the ground arching them near the plant's base to avoid breaking. Pin the canes down with crossed stakes to heel in canes. Lay a piece of burlap over the canes to make the springs uncovering operation easier. Then mound the soil over the entire plant and drive a stake into the ground at each corner of the mound to mark the spot.
Winter protection should be applied in late fall. If protection is applied too early in the fall, it interferes with the natural development of winter hardiness 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, fall cleanup should be completed, removing all plant debris and diseased parts. Even with these treatments, tip dieback can occur. This is not usually serious, as the canes should be pruned back at least 12 inches next spring and the injured tips will be removed at that time.
Fall pruning of roses should be restricted to removal of only tall, lank growth. It is important to remember that most varieties of roses will generally die back several inches during winter months. The degree of such dieback will determine the severity of next spring's pruning. Such dead wood should then be cut from the plant an inch or so below dark colored areas. Other pruning in the fall often results in canes that are too short next spring.
If you don't get a chance to mulch your roses, your only alternative is to depend on Mother Nature to mulch the garden herself. You know how snow is, it always falls where and when you lease want it.
If you would like more information on anything mentioned here please feel free to visit our web site or call UNH Cooperative Extension's Family, Home & Garden Center's Info-line (tollfree) at 1-877-398-4769. Trained volunteers are available to answer your questions Monday through Friday 9:00am to 2:00 p.m.