Winterizing Container Roses
Winter conditions in any zone are unpredictable. As a rule, your potted roses and rose trees should be kept in an environment above 25 degrees F, and ideally at 40 degrees, but not above 40-50 degrees or they will not go dormant. Keep this in mind as you select a method to overwinter your container rose. And do NOT prune roses in fall or growth will be encouraged. Wait until very early spring when still dormant.
And don’t think that just because you potted a super hardy rose that it will survive winter in a container. The soil in a container will freeze completely, whereas the ground will not. A hardy rose loses 2 or 3 hardiness zones in a container. In other words, a rose hardy in the ground to zone 3 will survive winter in a container without protection in zone 6, perhaps zone 5. A very large container, and therefore a large amount of soil, will help. It will take a longer period of consistently subfreezing temperatures to freeze the soil.
Generally speaking, potted roses and tree roses of any type should be able to weather a zone 7 winter outside with minimal protection steps. Stop fertilizing by the end of August or first week of September, but continue regular waterings right through winter. Less and less water will be used through the winter, but keep checking the soil at least every 3 to 4 weeks, as you do not want the roots to dry out. If at all possible, protect your rose from wind. Place the pots in an area sheltered from northern winds, and preferably in the shade but definately out of the late afternoon sun. The idea is to maintain a cold temperature so the rose remains dormant. Your rose may not remain dormant if it becomes too warm in a sunny area. A burlap wrap will help protect the rose or tree rose from both wind and sun, especially if the pot is so large that you cannot move it to a sheltered location. Tie the wrap loosely in place. If freezing weather is expected, move the pots up close to the foundation to benefit from the heat of the house, and add additional wrapping. A temporary covering of a blanket, heavy sheet or plastic should protect the plant from freezing for a short period.
To prepare container roses for winter in zone 6, stop fertilizing by the end of August or the first week of September, but continue regular waterings right through winter. Less and less water will be used throught the winter, but keep checking the soil at least every 3 to 4 weeks, as you do not want the roots to dry out. If you plan to overwinter your container rose outside, they should be in plastic or wood containers. Ceramic and terra cotta pots will crack if the endure freeze and thaw cycles. Right after the first frost winter protection should be applied, usually middle or late November. “Bury” the entire pot in leaves or mulch. Use some means of containing the mulching material, such as a chicken wire ring or a sack that allows air to flow such as burlap. Or bring the container into a shed or unheated garage for the winter. Be sure, however, that a garage stays cool enough to prevent the rose from growing. And don’t forget to water if you bring them inside, they tend to dry out more quickly in a closed shelter.
In zones 5 and colder, container roses must be either “Minnesota tipped” or brought into a shelter that does dip below 25 degrees F or above 40-50 degrees. Put simply, you need to completely bury your rose. This can be done pot and all, or you can dig out the rose and bury it bare root. If you keep a vegetable garden, that provides the perfect spot to bury a rose in its’ container. Stop fertilizing around mid August, but continue regular waterings until the rose is buried. About mid to late October after the first hard freeze, dig a hole and bury the pot or bare root rose. The bud union should be at least six inches deep, burying the pot on its’ side is fine and works well for a tree rose. If you prefer to keep the plant and container “clean” for easier spring removal, wrap it all in burlap. Once the ground has frozen, cover it with a thick layer of mulch to help maintain a constant soil temperature.
If your container rose can be stored in an unheated garage, be sure the temperature remains between 25 and 40-50 degrees F. Even in zone 5, overnight temperatures in a garage may dip below 25 degrees. The rose and container should be entirely wrapped in a heavy blanket and stored up on blocks so it is not in contact with the very cold cement floor. Place it in a corner that adjoins the heated house to borrow a little warmth. Some gardeners in the most northern regions have even rigged a light bulb inside coverings to maintain minimal warmth. Do use caution with such a method, making sure it is fire safe.
If you have an extremely large container that just cannot be buried or stored, do as much as you can to protect it. Place it up against the heated wall of a house or patio door - we lose a lot of heat through glass and your rose will make good use of it. Then heavily insulate the around the other three sides of the rose and container and hope for the best.
With proper care your roses can live their entire life in the container. Should your roses grow much larger than expected, transplant into a larger pot.