Winterizing Roses
Excerpt by Oliver E. Allen
line drawings by Elayne Sears.
While wild roses and other native species are assuredly programmed to endure the wide temperature swings of their areas, hybrid teas are for the most part descended from plants of frost-free or moderate regions and are thus naturally vulnerable to the onslaught of cold. Deep freezing breaks their cell walls and dries out their canes; overnight they turn black and are gone. So the prudent gardener must protect them.
The amount of protection a hybrid tea rose needs depends on the climate. If your temperatures stay below 20° F (7° C) for considerable periods of time without a predictable snow blanket to shield plants, protect your roses. If the ground freezes solid for most of the winter and temperatures are likely to drop below 10° F (-12° C), again without consistent snow cover, your hybrid teas will need covering. But if very low temperatures are infrequent and heavy rains keep the ground wet, the bushes are better left uncovered, as wetness encourages fungus diseases and other ills.
The time-honored
method of protecting hybrid tea bushes is to pile up dirt around
the base of the 
bush.
The process is known as hilling and is done just before the ground
is likely to freeze solid. The hill should reach a height of six
or eight inches (15 or 20 cm) if you are in a moderate zone, but
at least 12 inches (30 cm) in colder areas. What the dirt does is
conduct heat up from the ground (which even if frozen will be warmer
than air whipped by icy blasts) to the crown and lower reaches of
the bush; if that much of the bush survives the winter, the rest
(even though blackened) can be pruned away in the spring and the
bush will swiftly put out new growth to replace it.
As with most plants, the best guarantee of a rosebush’s survival through the winter is good care in the summer, particularly pest control. A vigorous bush will withstand cold’s rigors far more readily than a weakened one.
1.
Prune back. A couple of weeks after the first frost in your area,
but before deep freezing sets in, prune your rosebushes roughly
to eliminate any dead or weak shoots or any that show signs of disease.
Trim long canes by half and shorter ones by about a third. The aim
is to reduce each bush’s overall bulk so that it can be protected
most efficiently.
At the same
time, to help keep your bushes from drying out in the winter wind,
spray them with an antidesiccant not long after you have pruned
them. By sealing in moisture, the antidesiccant minimizes the
damage that can come from cycles of freezing, thawing, and refreezing
in midwinter.
2.
Bring dirt from elsewhere. In late November or early December, or
whenever you sense that the ground is about to freeze, bring dirt
from elsewhere in the garden and pile it around the base of your
plants to the desired height. Lean, sandy soil is better than a
humusy mix. Do not obtain it from between the plants, as that risks
exposing roots and crowns to freezing and so defeats the purpose
of hilling. Pat the mound firmly to make sure it encloses the canes
snugly.
3.
Add a mulch. Especially if you are in one of the colder zones, you
will want to add some kind of mulch -- salt hay, bark chips, pine
needles, leaves -- as extra protection, holding it in place perhaps
with evergreen boughs or other branches. The mulch further minimizes
the possible damage that can come from abrupt temperature swings
in midwinter.
4.
Be cautious about removal. In the spring, wait until the ground
has thawed for good before removing the dirt. But then remove it
promptly so that new growth is not damaged. Be sure to keep some
extra mulch on hand to pile temporarily around the base of your
plants in the event of a sudden late frost.
line drawings by Elayne Sears.
