Roses are resilient plants, but they are vulnerable to sudden and prolonged drops in temperature. Whether a rose bush needs covering is a localized decision, dictated by the specific location, the variety being grown, and the intensity of the incoming freeze. Preparing a rose for winter involves shielding the most sensitive parts of the plant from extreme conditions.
Assessing the Threat: When Protection is Necessary
A light frost, where surface temperatures fall between 32°F and 29°F, typically only harms new, tender growth and does not require covering established, dormant roses. The threshold for genuine danger is a hard freeze, defined as temperatures dropping below 28°F for an extended period. Temperatures below this point can cause significant damage to the rose’s canes and crown.
The hardiness zone is the first factor in determining a rose’s cold tolerance, indicating the average annual minimum winter temperature of your region. Roses planted outside their recommended zone, such as Hybrid Teas in colder climates (Zones 1-4), will require substantial protection to survive the winter. Even within the correct zone, a sudden, severe temperature plunge can still be damaging, especially if the rose has not yet fully entered dormancy.
The structure of the plant also impacts its vulnerability, particularly for grafted roses. A grafted rose consists of a desirable top variety joined to a hardier rootstock at the graft union. This union is especially susceptible to cold damage; if it dies, the original rose variety is lost and the rootstock may take over. Own-root roses, which grow on their own roots, are generally hardier and can regrow true to type even if the canes freeze to the ground.
Essential Pre-Freeze Preparation
Long-term winter preparation focuses on fortifying the base of the plant to protect the roots and crown area. As the weather cools in late fall, a deep watering is one of the first preparatory steps you can take. Moist soil retains heat much better than dry soil, acting as a thermal buffer that slows the temperature drop around the root zone. This deep, slow watering should continue until the ground is frozen solid.
The most effective way to protect the plant’s base is through hilling, which involves mounding insulating material around the lower canes. A pile of soil, shredded leaves, or compost 8 to 12 inches high should be placed directly over the crown and lower canes. This mound shields the vulnerable graft union from the damaging freeze-thaw cycles of winter. Using soil or compost is preferable to raking up the surrounding garden soil, which can expose shallow roots to the cold.
Immediate Freeze Protection Methods
When a sudden, severe hard freeze is forecast, temporary covers are necessary to protect the canes above the hilled base. The goal of covering is to trap the heat radiating from the ground and shield the canes from frigid wind. Suitable materials include burlap, commercial frost cloth, or old bed sheets, all of which allow the plant to breathe and moisture to escape. These covers should be draped over the entire bush and secured to the ground to prevent cold air from blowing underneath.
Avoid using heavy plastic sheeting directly on the canes, as this material traps moisture and creates a condensation layer that can freeze and cause cold burn. If covers are used for more than a couple of days during a sustained cold snap, they should be briefly opened on a warm, sunny day. This ventilation prevents excessive moisture buildup beneath the cover.
Using Cages for Insulation
For taller or more tender varieties, a cage constructed from wire mesh or stakes can be built around the rose. This cylinder is then filled with insulating material like straw, pine needles, or shredded leaves. This method provides an air pocket barrier around the canes for added protection.
Post-Freeze Care and Damage Assessment
Once the threat of freezing temperatures has passed, protective measures must be removed gradually. Covers should be taken off as temperatures stabilize, allowing the rose to acclimate to the spring air. The protective hilling mound should not be removed until the danger of a hard freeze is over, typically when new growth begins to appear in early spring. Removing the mound too early can expose the tender crown to a late-season frost, which can be just as damaging as a mid-winter freeze.
Assessing freeze damage requires patience; it is often best to wait for the plant to begin growing again before pruning. Freeze-damaged canes will appear blackened, shriveled, or discolored. The extent of the injury is determined by cutting back the canes until the pith, or center, is a healthy white or green color. Pruning dead wood encourages the plant to direct energy into new, vigorous cane growth, resulting in healthier and better blooms.