Roses are susceptible to freezing temperatures, which can cause significant damage or even plant death. Freezing occurs when ice crystals form inside the plant cells, rupturing the cell walls. This internal damage leads to the visible dieback of canes and tissues. A rose’s ability to survive depends on its genetic makeup, its state of dormancy, and the severity of the regional climate. Understanding a rose’s hardiness is the foundation for successfully growing these plants in any climate with a true winter.
How Cold Tolerance Varies Among Rose Types
A rose’s inherent cold tolerance is categorized using the USDA Plant Hardiness Zone system, based on the average annual minimum winter temperature of a region. Certain rose classifications handle much lower temperatures than others due to their breeding. Less cold-tolerant varieties, such as Hybrid Teas and Floribundas, often suffer extensive cane death in regions colder than USDA Zone 7 without significant winter protection. These types are particularly vulnerable because they tend to be grafted, meaning the desirable rose variety is fused onto a hardier rootstock.
The graft union, the point where the two parts join, is often the most susceptible part of the plant to cold injury. If the graft union freezes and dies, the entire desired rose is lost, and only the hardy rootstock will grow back. Conversely, Shrub roses and species roses like Rosa rugosa are known for their exceptional cold hardiness, often surviving unprotected in Zones 2 or 3. Many modern shrub varieties are grown on their “own roots,” meaning the entire plant is the desired variety, allowing it to regenerate even if the canes freeze completely to the ground.
Identifying Symptoms of Cold Damage
Gardeners should inspect their roses in early spring for signs of freeze damage, which usually manifests as cane dieback. Canes affected by cold will appear withered, shriveled, or entirely blackened, especially toward the tips. This darkened, dead tissue indicates that the internal cell structures have collapsed from ice expansion.
Another symptom is split bark, where the outer layer of the cane has cracked or peeled away due to rapid temperature fluctuations. Damage to the plant’s crown, the swollen area at the base where the canes meet the roots, is the most severe form of cold injury and may result in the death of the entire plant. When pruning damaged canes, a cross-section of the stem will reveal brown or discolored pith, confirming that the tissue has been killed by the cold.
Essential Winter Protection Methods
The primary goal of winter protection is to maintain a consistently cold temperature at the plant’s crown and roots, preventing the damaging cycle of freezing and thawing. Protection should be applied only after the rose has entered full dormancy, typically after two or more hard freezes have caused the leaves to drop. Prematurely covering a rose can trap warmth and moisture, potentially encouraging disease or tender new growth that will be killed by the next freeze.
One of the most effective methods, particularly for grafted roses, is hilling, which involves mounding insulating material around the base of the plant. Gardeners should pile 10 to 12 inches of soil, compost, or shredded bark directly over the crown and the lower parts of the canes. It is important to bring in new soil from another area rather than scraping up the existing soil, as excavating around the base can damage surface roots and create a water-collecting basin.
In extremely cold climates (USDA Zone 5 and colder), an additional layer of protection is necessary for the remaining canes. This involves creating a protective cylinder, or cage, around the rose bush using wire mesh or a plastic rose cone. The cylinder should be placed over the hilled base and then filled with a light, airy insulating material such as straw, pine boughs, or shredded leaves.
The insulating material must be dry to prevent rot. The top of the cage should remain open or have ventilation holes to allow air circulation and prevent overheating on sunny winter days. Before installing the cage, long canes should be gently tied together with twine and cut back just enough to fit within the enclosure. This preparatory pruning prevents the canes from being whipped around by winter winds, which can loosen the hilled soil or damage the cane structure.
Post-Winter Recovery and Pruning
The process of removing winter protection in the spring must be timed correctly to avoid shocking the plant. Once the danger of a hard freeze has passed and the ground has thawed, the insulating material should be gradually removed over several days or weeks. This slow acclimation allows the plant to adjust to spring temperatures and sunlight, preventing new growth from being scorched.
The hilled soil or mulch mound should be gently spread away from the crown once all risk of a severe freeze has ended. Spring is the time for corrective pruning to remove the canes damaged over the winter. Gardeners should use sharp, sterilized pruners to cut the dead, discolored wood back until a healthy, white- or cream-colored pith is visible in the center of the cane.
Each cut should be made at a slight angle, approximately one-quarter inch above a bud facing away from the center of the bush. Pruning to an outward-facing bud directs the new growth away from the plant’s interior, promoting better air circulation and a strong, open structure. Even if a rose appears dead, cutting the canes back to the ground may reveal a living crown, allowing the rose to regenerate and flourish later in the season.