Friday, October 12, 2007
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. They 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. In general, roses grown in USDA Zones 8 to 10 need no special precautions, while those in Zones 6 and 7 will probably require covering and those in 5 and below most surely will. Another guideline: If your temperatures stay below 20 degrees Fahrenheit for considerable periods of time without a predictable snow blanket to shield plants, protect your roses. Still another: If the ground freezes solid for most of the winter and temperatures are likely to drop below 10 degrees, again without consistent snow cover, your hybrid teas will need covering. 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. Although specially made plastic coverings can be purchased, the time-honored (and perhaps simplest) 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 if you are in a moderate zone, but at least 12 inches in colder areas (Zones 6 and colder). The soil conducts 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. On the other hand, take care not to stimulate your roses unduly as autumn approaches lest they put out new growth that will not be tough enough: cease fertilizing by summer’s end, and stop deadheading spent blossoms at about the same time. 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 most efficiently protected. Don’t worry about such fine points as the location of buds; that can be addressed in the spring when you do precise pruning. At the same time, to help keep your bushes from drying out in the winter wind (dryness is if anything more of a threat to them than cold), 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. 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.