In many areas across North America, cold winter temperatures are a challenge for potted plants. Despite being quite winter hardy, roses are no exception.
Why Pots Need Extra Care
The challenges for potted roses are temperature and moisture. Roses planted in the garden have the advantage that the earth insulates the roots and keeps temperatures and moisture levels more consistent.
Pots raised above the ground come with more volatile changes to the soil the roots reside in. For instance, rose roots freeze quickly, then winter sun warms the pots and raises the temperature, and at times, even to the point of thawing. These temperature variations can cause damage and even the loss of the plant. Dry winter winds and winter precipitation also challenge moisture levels, either by drying out the rose canes or by soaking the potted soil. Excess moisture is particularly a risk if your garden pot does not drain well.
Protection
Wait until your area has experienced a few frosts, which help move roses into dormancy. Then choose a method that best suits your potted roses and the space you have available.
An Unheated Garage Or Shed
This is the ideal option. A consistently cool space away from any windows and direct sunlight will offer excellent protection from temperature fluctuations. Check the soil once every 2-4 weeks. The soil should be slightly moist. Add a small amount of water as necessary.
For our zone CA-7a (US-6b), we suggest bringing pots in at the end of November once temperatures have dropped. This allows them to experience some frosts and cold weather pushing them into dormancy first. Depending on your garden zone, you may need to adjust this timeline. It’s best to move them before temperatures drop lower than about -4°C (25°F).
Sheltering Outdoors
If you have no garage or garden shed, you can overwinter the roses outdoors.
Small pots: If you have space in the garden, one option is to dig a hole and bury the pot, then dig it out again in the spring.
Pots of any size: Find a sheltered area of the garden and cluster the pots together. Top up each one with extra soil making a hill around the crown of the plant. Wrap the canes in a breathable fabric such as cotton or burlap to protect them from the wind. Evergreen boughs from Christmas trees can also be tied around rose canes to create a tent of protection. Consider purchasing a bale or two of straw to stack around the group as insulation.
Large pots: Larger pots are better insulated since the additional soil around the roots helps keep the temperature more even. However, their size makes them very difficult to move. Following the same as above, top up all pots with extra soil, hilling it up around the crown of the plant. Wrap with protective fabric or evergreen boughs and consider using straw bales as insulation as well. If you are able to move them to a sheltered area, do so, clustering them together keeping smaller pots surrounded by the larger ones.
Another option: If moving pots around is not possible, save room in the garden for planting these roses directly in the ground for winter. Be sure to bury the grafting union by 2.5-8cm (1-3 inches). The ground soil will solve the challenges of temperature regulation and allow excess moisture to drain away. Dig them up again in the spring while they are still dormant and return them to your pots for another season of elevated growth.
A Few Extra Tips
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Select roses that are cold hardy down to a zone or two colder than your own. This gives potted roses a helpful advantage against low winter temperatures.
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Rootstock winter hardiness varies from cultivar to cultivar. Those roses that are grafted and grown on Rosa multiflora benefit from its cold hardy qualities.
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Resist the urge to prune over winter. Give your pruners a rest until spring.
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For tips on choosing a rose and a pot, see our resource on Potted and Container Roses.
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For care specific to your growing zone, your local Rose Society, Horticultural Society or Garden Club is a great resource.
Spring Transition
Moving pots straight from a garage or shed into full sun can shock them, so bring them out gradually. In our zone CA-7a (US-6b), April 1st is often used as a guideline. Move the potted roses to a sheltered spot, then into full sun over several days. If a hard frost, prolonged wind, or nighttime temperatures below -4°C (25°F) are forecast after buds start to swell, move them back into shelter.
None of these steps are complicated, but protecting potted roses in a cold climate does take a little thoughtful care and time. Beautiful blooms are your reward, waiting for you next season.
Photo of Boscobel™ courtesy of David Austin®
