Louise Coleman, firstname.lastname@example.org, Consulting Rosarian, Eastchester, NY
If you live in a part of the country without winter, lucky you! The rest of us must deal with the problem of winterizing roses. Winter hardiness of roses is subject to many variables, mostly the micro-climate of your garden and the fluctuations of the weather. Some varieties can withstand the winter better than others.
Be assured there is no one right way to protect roses from fluctuating temperatures and icy winds. If you have never protected your roses bushes and have lost few or none, then there is no need to start now, except for new bushes planted last spring. How much protection your bushes need will depend on their particular spot in your garden. Bushes planted near the house are already protected to some degree. Spots in the garden that are sheltered by shrubs or walls from icy winds will also require little protection. However, the bushes out in the open and especially those in low ground, may require the full treatment.
Winter survival of roses depends as much on the condition of the bushes in autumn than on any type of winter covering. Sickly bushes may not make it through the winter no matter what you do. Those bushes heavily infected with black spot and/or mildew will be at greater risk of serious damage than the healthy bushes.
What causes winter damage?
The plant cells of roses contain a lot of water, water freezes and expands. This expansion ruptures the cells, damaging and even killing them. Cold temperatures alone are not harmful as the bushes become dormant. The trick to successful plant protection is to keep them dormant. If you apply your winter protection before the ground surface is frozen, you will delay dormancy by keeping the soil warm with your cover. Therefore, it is important to wait for the right time! Some roses have the ability to convert water to a form that doesn’t freeze. This ability is an inherited characteristic that makes the variety “hardy.”
Pruning roses in the fall makes then more subject to winter damage as it encourages the sap to rise to form new tender growth. The sap freezes and the plant is damaged.
Another cause of damage can to be due to drying out of canes exposed to high winds at low humidity. The roots are dormant and cannot supply more moisture to the canes. Often the bushes could survive better in a more protected situation. There are many easy ways to create this protection; a snow fence, burlap screen or some protective covering will do the job. You might even try spraying with Wilt-Pruf® to cut down on moisture loss. Some growers are successful just using evergreen branches or discarded Christmas trees to cover the roses.
The other side of the coin is too much moisture. A heavy mulch of soggy maple leaves can wreck havoc. Mulch with materials that will not hold so much water – oak leaves, pine needles, salt hay, etc. Piled high on the bushes, these materials will also protect the canes from wind damage.
Before using any winter protection method, it is important to clean off the surface of the rose beds to prevent overwintering of diseases. If possible, one last spray for fungus is advisable. Some rosarians like to use a dormant spray at this time.
There are many ways to winter protect roses. But if your present methods work – don’t change. Protection can be as simple as heaping leaves in the rose bed or as elaborate as making styrofoam boxes.
Let’s start with the simplest to winterize – the minis. Once they are completely dormant just cover with several inches of leaves. That’ s it!
Hybrid teas, grandifloras and floribundas are a bit more work. Trim tall dormant bushes to about 5 ft. to prevent them from rocking in the wind. Some bushes may need to be tied up and staked.
Secure climbers by tying and staking, as trimming will reduce spring bloom.
The oldest method of protecting roses is hilling with 10 to 12 inches of soil. Never scoop up the soil around the bushes as this exposes their roots. It is better to use some material that can be spread as a mulch in the spring. Compost is a good choice but be sure the ground is lightly frozen before applying any hilling. In many areas a cover of straw will do the job.
In colder areas, it may be advisable to first mound the bushes then add the straw cover to protect the canes. Gutter screening, commercial collars or good old newspapers (several layers folded in half) can be used to hold the hilling material in place.
In order to help us solve our question, we might ask: “Are there any scientific studies to help us determine whether winter protection is necessary or not?” There are but they only help to muddle the issue. In Chicago, results of overwintering records—8,500 of them during the fifties— seemed to prove Dr. Westcott’s later contention that winterizing was not essential. The best type of winter protection resulted in over twice the percentage of plants lost than when no protection at all was used. No one could deny that that seemed to bear out Miss Westcott’s conclusion. But, during the same years, in Cincinnati records were kept on 2,700 plants and the results clouded the issue, in fact, one could say the results were stunning, because they came to the opposite conclusion. Eight times as many unprotected plants were lost percentagewise as were protected plants. What could one say, except that “winter protection is necessary, maybe.”
In lieu of cones, you can construct styrofoam boxes to protect several plants at one time. Its easy! A box to cover several plants can be made with 2″ thick styrofoam sheets. Put 3 sets of stakes in side by side (2″x 2″ boards 2 feet high) and 2 feet apart to hold a 2″ x 8″ sheet of styrofoam to form one side. Do the same for the other side and the ends. Slide the styrofoam in place, butting the ends as close as possible. Another sheet is used for the top and bricks are placed on the corners to hold the top in place. If your box must be wider than two feet, glue pieces for the right size to form the top. It helps to tie a rope around the box to keep it firmly in place.
Boxes can be made in smaller sizes using the same method. The box works very well. All foliage must be removed from the plants and the surface of the ground should be free of any debris. There is more flexibility with the box as the plants do not have to be tied and the sides can be put in place before a hard frost, leaving the top off until the ground is frozen. This allows for a quick cover-up and you can do most of the work without freezing yourself. If your roses suffer damage or death due to the ravages of winter, try some of the methods here. I hope this information helps your roses make it safely through the winter, rewarding your efforts with healthier bushes in the spring.
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