Roses vary quite a bit in their cold hardiness across different rose classes and even among different varieties in the same class. Gardeners in cold climates should take care to select varieties appropriate for their hardiness zone, to minimize the need for extensive winter protection.
All but the hardiest shrub roses may require protection when grown in cold climates where winter temperatures fall below 0°F (zone 7 and below). With good variety choice, gardeners in zone 6 and above usually do not need to make significant efforts to protect roses in winter.
There are multiple methods for providing winter protection to roses. These guidelines provide an overview of the options and include enough information to successfully winter rose plants in cold climates.
Gardeners should choose and plant varieties appropriate for their climate. “Own root” varieties that are not grafted may be a better choice than grafted roses for gardeners in very cold climates, as these varieties can regrow from their roots if severely damaged by extremely cold winter conditions.
Good Culture Promotes Hardiness
Planting rises in a good site with well-drained soil helps to ensure they survive winter. A heavy, poorly drained soil makes successful overwintering much more difficult.
Vigorous, healthy roses are more hardy than weak, stressed, or diseased plants. Good culture throughout the growing season, including protecting plants from insect and disease damage and watering and fertilizing on a timely basis, is an important foundation for winter survival.
Stop fertilizing roses by the end of July. Although it is important to keep a plant vigorous and healthy through the growing season, fertilizing too late in the season promotes excessive late growth that may not harden off fully before winter. In areas north of Madison, we recommended fertilizing be discontinued by the middle of July.
Allow September blooms to remain on plants. Removing spent blooms encourages new growth and continued blooming. By allowing September blooms to remain on the plants, plants are signaled to begin preparing for winter dormancy.
Fall Clean Up
Thoroughly clean up leaves and flowers after a killing frost. Once temperatures have fallen into the lower twenties, rose plants will have stopped growing. At this time the leaves, flowers, and any small or twiggy growth can be removed from plants. If black spot has been a problem in the past season, this practice is very important to reduce disease pressure the next year.
Plants and the surrounding soil can also be sprayed with a horticultural oil spray to further reduce the survival of overwintering of pests and diseases. Always read and follow label directions carefully when using pesticide sprays.
Water plants thoroughly just before the ground freezes. A final soaking in late fall helps protect roses from desiccation during winter.
Tie the canes together with a soft cloth before the ground freezes. This helps make plants more manageable to work with when taking further protective measures.
The most traditional way to protect rose crowns is in winter is “hilling up.” This is done by mounding six to ten inches of soil or compost over the crowns of plants. The soil or compost should not be taken from around the bases of the plants, but from another location. If roses were planted with the graft 2 to 3 inches below the soil surface, six inches of soil should be sufficient (see Figure 1). If the graft was not covered at planting or you know from past experience that a variety is particularly tender, increase the covering to ten inches.
After the ground has frozen lightly, cover the mounded plant with an organic mulch like straw, marsh hay, bark, pine boughs, or shredded leaves. Apply the mulch 6 to 12 inches deep. If your plants are in an open or windy site, use a wire cage, collar of fiberglass or tar paper, or burlap covering to hold the mulch in place (see Figure 2).
Rose cones are another option for winter protection. When using rose cones, select a cone large enough to not require significant cutting back of the canes. Trim canes just enough so the cone completely covers the plant (see Figure 3).
Punch 4 to 6 pencil sized holes in the top and bottom of each cone to ensure there is good ventilation. Heat can build up inside cones that are not ventilated and reduce overwintering success. Make sure cones will not blow away by anchoring them with soil, bricks, stones, or stakes.
In colder climates, or for more tender varieties, some gardeners cut the tops off of cones and fill them with organic mulch.
Tree roses, sometimes called “rose standards” are hybrid tea or floribunda roses grafted with a tall trunk. Tree roses are very tender and require special protection in winter because their graft unions are exposed.
There are three general ways to winter tree roses. The first method is for tree roses growing in containers. Containerized plants can be moved to a protected location before the soil freezes, usually around the first part of November. Ideally, the location maintains a temperature just above freezing from November through March. This is cool enough to keep plants dormant but warm enough to prevent winter damage. Unheated attached garages, glassed in porches, and minimally heated greenhouses are examples of structures that have worked for many northern gardeners.
The second option is trenching (sometimes called the “Minnesota tip”, as it is also used to protect regular roses in very cold climates.) In this method, an entire plant is buried in a horizontal trench large enough to accommodate the entire tree rose including the roots (see Figure 4). Before the ground freezes, dig up the dormant tree rose or potted plant and lay it horizontally in the trench, covering all parts with a minimum of six inches of soil.
Instead of completely digging up plants, they can be “tipped” by loosening the soil opposite the trench with a garden fork. Carefully use the fork to tip the plant over into the trench, leaving some of the roots anchored in the soil.
After the soil freezes lightly, cover the trench with 12 to 18 inches of mulch. Remove the mulch in early spring and remove the soil as it thaws, then replant the tree rose.
The final method is to hill up soil at the base of the tree rose, then wrap and mulch the upper part of the plant with an organic mulch held in place with a burlap wrap, chicken wire, or a wood frame. There should be 12 to 18 inches of mulch around the entire plant.
Most climbing roses bloom on wood produced the previous season, so winter protection is essential for maximum performance in all but the most protected sites. Winterizing climbing roses is best done by laying the canes down, staking them to the ground and covering them with 4 to 6 inches of soil just before the ground freezes (see Figure 5). Cover the soil mound with 6 to 12 inches of mulch after the soil freezes lightly. If the canes can’t be brought down, they can be tied together and insulated with straw. Hill up the base of the plant with soil, then pack straw around the canes and wrap the entire bundle with burlap to hold mulch in place (see Figure 6).
Removing Winter Protection
Winter protection can be gradually removed in the spring as the soil thaws. This is generally in early to mid-April in southern Wisconsin. Any additional pruning needed can be done at this time. In the event of unseasonably cold weather after the plants have resumed growth, provide temporary protection by covering them with a sheet, plastic, or a floating row cover.
Allen R. Pyle is the lead horticulturalist at Jung Seed Co. and has been a professional horticulturist for over 20 years, with decades of experience in gardening and landscaping. Allen has degrees in both horticulture and entomology from Michigan State University. He has extensive experience in plant propagation, pest management, growing perennials, and organic gardening. His knowledge spans a wide range of plants, including edibles, ornamentals, herbs, weeds, and native species. Allen is passionate about plants and gardening and is always happy to share his knowledge and expertise with others. He regularly speaks and writes on plant-related topics for both professional and amateur gardening audiences. Allen is also certified in Permaculture design.