What is the best way to cover in ground roses during hard freezes?Updated a month ago
To protect in-ground roses, especially in warmer regions like most of California and Texas, you can use a combination of methods to safeguard the plants on the rare occasions there is a hard freeze. My farm is also located in zone 9b and in the last 10 years I haven't needed to do any hard freeze protection in my cut flower rose production field. While frost advisories and freeze watches are typical in the winter, hard freeze warnings are a rare occurrence.
Before taking steps to protect your roses, it's crucial to determine when such protection is truly necessary. For instance, frost advisories, freeze warnings, and freeze watches usually do not require any protective measures for roses. (Check out this helpful article that outlines the various types of cold warnings and their impact on roses.) Your question specifically addresses "hard freezes," which the National Weather Service (NWS) defines as periods when temperatures are expected to drop below 28°F for an extended duration. I will focus on options for protecting roses specifically during these "hard freezes," as the other types of freezes and frosts do not necessitate protective actions.
Step 1: In fall or early winter, avoid heavy pruning, as this encourages new growth that is more vulnerable to freezing. Lightly shape prune any damaged, tall or weak canes, but leave most of the structure intact for added cold resistance. (Click here for more info on fall shape pruning.)
Step 2: Water throughly before freezing as moist soil holds heat better than dry soil. Watering your roses thoroughly before a freeze can help maintain warmer soil temperatures and reduce the impact of cold air on the roots.
Step 3: Mound soil or mulch around the base of the rose as soon as you expect temperatures and conditions will be there for a hard freeze. Pile a mound of soil, compost, or mulch (about 8-12 inches high) around the base of each rose bush. This insulates the root zone and protects the graft union (if the rose is grafted). Make sure the mulch or soil is loose, not packed, to allow for some airflow.
Step 4: For added protection after mounding soil, consider wrapping the canes with a layer of materials such as burlap, frost cloth, or horticultural fleece. Secure the wrapping around the plants using stakes or twine to shield the canes from frost damage and drying winds. While blanket-style coverings provide good protection, I personally prefer a zip-up drawstring frost cover. This option allows for quick and easy wrapping around your plants, and they can be effortlessly removed once the freeze has passed—no need for additional stakes or securing. Avoid using plastic as a cover, as it can trap moisture and lead to rot.
Step 5: Once the threat of freeze has passed, gradually remove the protective materials to allow the roses to acclimate naturally to the warming temperatures. The cover does not need to stay on all winter long in mild climates like zone 9b. It's best to remove when the hard freeze has passed. Do not leave the covers on all winter.