Grafted roses such as hybrid teas, floribundas and grandifloras need winter protection almost everywhere in Minnesota. The fix is a mound of bagged soil, 10 to 12 inches deep, over the base of the plant. It goes on after a run of hard freezes, usually early to mid November in the Twin Cities. Hardy own-root shrub roses can often skip it. If you are still deciding what to plant, start with the overview on growing roses in Minnesota.
Do roses need winter protection in Minnesota?
It depends on the rose, and the climate sets the stakes. Minnesota runs from USDA hardiness zone 3a to 5a. The USDA system rests on a single number: the average coldest night of the year. The Twin Cities, in the southern half of the state, sit in the milder part of the state’s hardiness zone range, where winter cold is less severe than in the north. Northern Minnesota slides toward the colder end of the state’s hardiness zone range, where winter cold is far more severe. Other parts of the state fall between those two, so check your own spot before you copy anyone’s schedule.
Those lows matter because of how a grafted rose is built. The top is a named variety joined to a tougher rootstock, and the join is a swollen knob at the base called the graft union. Canes above the snow line often die back in a Minnesota winter, and that is survivable. A frozen graft union is not. When it dies, the plant regrows from the rootstock, which sends up the wild rose it was grafted onto. You pay for a hybrid tea and end up with something else.
Roses growing on their own roots and bred for the north are a different story. Many of them tolerate cold winters with nothing more than a blanket of snow. They may lose cane tips, but they regrow from the base. In much of the state, a hardy own-root shrub rose usually does not need mounding, and fussing over it wastes a weekend. The Roses That Hold Up in Minnesota page sorts out which types fall into that group.
Snow cover changes the odds for every rose. A deep, early snowfall insulates the base the way a quilt does. A bare, dry, windy winter strips that insulation, and a January thaw followed by a hard refreeze can do more damage than steady cold. Mounding is insurance against the winters when the snow does not show up on time.
When to start, and what triggers it
The trigger is a run of hard freezes. The calendar only tells you roughly when to expect one. NOAA NCEI’s 1991-2020 Climate Normals for the Twin Cities put the first 32°F freeze between October 11 and October 23, and the last one in spring between April 17 and April 30. Those are ranges, because any given year can fall early or late within them.
The first frost is the wrong signal. It tells the plant to slow down, but the soil is still warm and the canes are still alive. Pile soil on at that point and you hold warmth and moisture against the base. The plant keeps pushing soft growth underneath, and that growth is what rots. Wait until nights hold at or below freezing, daytime highs stay barely above freezing, the leaves have yellowed and growth has stopped. In the Twin Cities that usually arrives in early to mid November, a few weeks after the first frost.
Farther north the whole season is compressed. Northern Minnesota’s season is compressed at both ends, by several weeks in the far north, so winter arrives sooner and spring comes later. A gardener near the Canadian border will hit the trigger earlier than someone in Minneapolis, and should uncover correspondingly later in spring.
| Timing marker | Twin Cities (reference city) | Northern Minnesota |
|---|---|---|
| Last spring frost (32°F) | April 17 to April 30 | Several weeks later |
| First fall frost (32°F) | October 11 to October 23 | Several weeks earlier |
| Mounding window | After a run of hard freezes, usually early to mid November | Same trigger, reached sooner |
How to mound, and how deep
The graft union is what you are burying. The canes matter much less. Once the plant is dormant, the goal is to put an insulating layer of soil around the base so the union stays at a steady, cold-but-not-brutal temperature. The canes above can freeze, and you can deal with them in spring.
- Water deeply once or twice if autumn has been dry, then let the soil drain before the ground freezes.
- Gather the canes loosely and shorten only the very tallest, enough that winter wind cannot rock the plant in its hole. Save the real pruning for spring.
- Pour bagged soil over the base until you have a cone 10 to 12 inches deep, covering the union and the lowest part of the canes. Plan on a generous amount per plant.
- After the ground freezes solid, add a loose layer of straw, shredded leaves or evergreen boughs over the cone to hold snow in place.
Using bagged soil instead of soil scraped from around the plant has a practical reason. Digging beside the rose exposes the shallow roots near the crown, and the trench you leave fills with meltwater that freezes into ice around the plant. Garden soil can also carry the leaf-spot spores that built up in the bed over summer, and you would be packing them against the canes all winter. Bagged topsoil or a bagged soil and compost blend comes in clean and drains evenly. Fresh soil from another part of the yard works too, as long as it did not come out of the rose bed.
In spring, the job runs in reverse. Pull the straw first, then take the soil off in stages as the last spring frost window approaches, which runs April 17 to April 30 in the Twin Cities and later in the north. Pick a cloudy day, and keep some straw handy in case a hard freeze returns. Once the buds begin to swell and you can see which canes are alive, follow the timing on When to Prune Roses in Minnesota. Whatever you do, leave the mound on until the worst freezes have passed, because a plant uncovered in early April can lose its swelling buds to one cold night.
What does not work in this climate
Plastic wrapping looks protective and does the opposite. Clear or black plastic heats up on a sunny January afternoon and traps moisture against the canes. The plant warms up, starts to wake, and then the temperature drops overnight. Condensation inside the wrap leads to mold and cane rot, and plastic offers almost no insulation against deep cold. Burlap or a breathable cover of straw at least lets moisture escape.
Rose cones sealed shut have the same flaw. A foam cone is meant to be a shelter, but a closed cone gets warm in winter sun, lets damp air collect inside, and becomes a snug nest for mice that can chew the canes. A cone also sits on top of the plant without covering the graft union with soil, and a light cone can blow over in a prairie wind. If you already own cones, fill them with soil or straw and vent them on mild days. They work best as a topper over a proper soil mound.
The third mistake is mulch piled on while the ground is still warm. Heavy mulch in October holds the earth’s summer heat in, keeps the plant growing, and gives fungus a damp, sheltered home against the base of the canes. Mulch should go on after the ground freezes, so it keeps the soil cold and steady through January thaws instead of keeping it warm. In short, wait for the hard freezes before covering anything, whatever the material.
Checking this against your own county
Minnesota has too many microclimates for one schedule to fit. University of Minnesota Extension has county offices and Master Gardener volunteers who know local growing conditions in your area. Elevation matters as well. Cold air drains downhill and pools in low spots, so a yard at the bottom of a slope can freeze earlier and harder than one on a rise a few blocks away. A city yard near pavement and buildings runs warmer than open farmland. Ask your county extension office about local conditions before you set the date to mound.
Common questions
Can I cover my roses with a pile of fallen leaves?
Whole leaves mat down, hold water against the canes and can rot the base. Shredded leaves work as a top layer over a soil mound after the ground has frozen. They should not be the only protection.
Do climbing roses need different protection?
Hardy climbers can stay on the trellis. Tender grafted climbers need more work: untie the canes, lay them down gently along the ground, and cover the whole length with soil and straw. Bend them slowly, because frozen canes snap.
What about roses in pots?
A pot freezes from the sides, leaving the roots far colder than they would be in the ground. Move the pot to an unheated garage or shed once the plant is dormant, or sink it into the garden and mound over it. Check the soil once or twice over winter so it does not dry out completely.
Should I water roses before winter?
Yes, if autumn has been dry. A deep watering before the ground freezes keeps the roots from drying out over winter, since dormant roses still lose moisture to cold wind. Water well, let it drain, and then mound once the hard freezes arrive.