Winter Protection for Your Roses
By Stan Barrett, Master Gardener, Colorado State University Cooperative
Extension, Denver County
One of the most important things you can do for the winter safety of your roses is to
keep them in good health during the summer. A rose that goes into dormancy after
several months of being properly fed and watered and kept reasonably free of diseases and
insect pests can realize its full hardiness potential. By contrast, the unfortunate
plant that is stressed and unhealthy will struggle to survive the rigors of winter.
It is quite possible to provide a reasonable degree of winter protection to roses
without going to an enormous amount of trouble. By preparing the roses before they go into
dormancy, allowing them to gradually go dormant, then insulating them from temperature
fluctuations, you can help their natural defense system to operate properly, with good
expectation of success.
What causes winter damage?
In order to understand what winter protection techniques are likely to be successful
you need to first understand the mechanism of winter damage. During the growing season the
plant cells of a rose contain water. If a sudden drop in temperature occurs, this water
can freeze. The subsequent expansion ruptures the cells, damaging or even killing
them. On the other hand, if the rose is allowed to go slowly into dormancy, the cell
walls thicken and the water is converted to a form that resists freezing. This new
liquid is quite literally--antifreeze! The degree to which the rose can make this
conversion defines its cold-hardiness.
Timing is important
After the rose is dormant it can withstand very low temperatures without harm, so the
trick to successful plant protection is to keep the plant dormant. If you apply winter
protection too early (before the ground is frozen) you will delay dormancy by keeping the
Step to take in preparing roses for winter
- Don't fertilize after the end of August. Fertilizing encourages the
growth of new shoots. If you have new shoots starting to grow from the base of the plant
in September, remove them to prevent early-freeze injury to the bush.
- Gradually reduce watering, starting around the beginning of September.
This will allow the plants to begin their hardening-off process in preparation for
- Clean up dead leaves and debris from around the base of the roses. This
will eliminate a hospitable environment for over-wintering insects or diseases.
- Apply a Dormant Oil spray to the canes and the soil surface if your
roses had serious insect problems during the summer. You must be sure the roses are
dormant before taking this step.
- Avoid dehydration. In Denver, another cause of winter damage is the low
humidity, combined with intense winter sunshine and wind. One way to combat this
dehydration, is to spray the plant with an antidessicant such as Wilt-Pruf as soon as it
is dormant. Roses should also be watered every three weeks or so if the winter is dry.
- Don't do any serious pruning in the fall. You may want to shorten any
extra long canes that could break from high winds or heavy snow, but otherwise prune your
roses no earlier than the end of April.
Different types of roses and their specific needs
- Miniatures: Most miniatures are very hardy and require a minimum of
winter protection. Because they are usually small they are easy to protect; simply
mound up mulch around the stems to a depth of 4 to 6 inches, plus three inches on the soil
around the plant. Mulch can be ground-up bark, loosely packed straw, chipped evergreen
boughs, shredded leaves or soil. If you use soil, bring it from a location away from the
rose bed. Using the soil that is already around the rose would expose and damage the
surface roots. Remove the mulch very gradually in the spring to allow any new growth to
become acclimated to the sun and wind.
- Shrub & old garden roses: Most of these roses are very winter
hardy. You may not need to do anything in the way of added protection, although a
little mounding up of mulch would provide additional insurance. Some of the new
David Austin shrub roses have not yet proven how hardy they are, so you may want to
protect them and any others that you feel might be questionably hardy.
- Floribundas and polyanthas: These types of roses are usually somewhat
hardier than the hybrid teas, but still benefit from receiving winter protection. They can
be treated in the same way as the Miniatures, using mulch to maintain dormancy.
- Hybrid teas and grandifloras: When purchasing a hybrid tea or
grandiflora rose, be sure to buy only those that are known to be hardy for this location.
The traditional way to protect these roses is to cover the base with 12 or more
inches of mulch. It is a good idea to contain the mulch somehow to prevent it being
blown away. This can be done with the use of a wire mesh cylinder about 12 inches in
diameter. Rose "collars" made of plastic sheeting, and serving the same purpose,
are available at most garden centers. Again, the mulch must be removed gradually, starting
around mid-April. Another device on the market is a foam cone which fits over the rose.
Unfortunately, the rose must be pruned quite drastically to accommodate the
come. The come may also allow the rose to heat up during warm spells, possibly
leading to breaking the plant's dormancy and stimulating shoot growth.
- Climbers: As a general rule, climbing cultivars of the hybrid
teas (such as Climbing Peace) are not recommended for our area, as they often do not
survive the winter. However, many of the so-called "large-flowered climbers"
(such as Blaze, America, New Dawn) have been very successful here. A recent
introduction from Canada, William Baffin, has been called "the first truly hardy
climber".Because of their height, climbers are fairly difficult to protect. One
method used is to take the climber canes off of their supports after they are dormant and
secure them to the ground,then totally cover the canes with mounded mulch. Another
method is to leave the canes on their supports and wrap the whole assemble with burlap.
Not surprisingly, many growers of climbing roses in the Denver area simply mulch the graft
area and tie the canes firmly in place to avoid wind damage. In most years this approach
seems to be adequate.
- Standard or "tree" roses: Because the graft union is so
exposed on standards, these are the most difficult types to protect in the winter and
their popularity is limited for that reason. You can either wrap the rose in burlap,
starting at soil level and going high enough to cover the graft, or loosen the soil around
the roots at one side and lean it over into a trench, then cover the whole plant with
mulch. Another alternative is to dig up the tree rose (or else grow it in a
container) and store it in a cool garage or basement until spring.
Photograph courtesy of Judy Sedbrook.
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