Yes, for most garden roses. Winnipeg sits in Canadian hardiness zone 3b, and grafted roses such as hybrid teas and floribundas will not reliably survive a Manitoba winter without a mound of soil over the base. Start only after a run of hard freezes, usually late October into early November. Hardy own-root roses can often get by on snow cover alone. This is the winter chapter of growing roses in Manitoba.
Do roses need winter protection in Manitoba?
Natural Resources Canada places Winnipeg in Canadian plant hardiness zone 3b. That system blends seven climate variables, so it cannot be converted to a USDA zone, and a “3b” in a US catalog describes a different climate. In practical terms, a normal Winnipeg winter brings long stretches of nights well below freezing, drying wind and few mid-winter thaws that last. Environment and Climate Change Canada’s long-term averages for the Winnipeg airport station give about 122 frost-free days, between a mean last spring frost of May 23 and a mean first fall frost of September 22. Both dates are midpoints. In one year out of two the last spring frost comes later than May 23, and in one year out of two the first fall frost arrives earlier than September 22. Northern and upland districts run weeks behind the city.
Which roses need protection in zone 3b?
Anything grafted. Hybrid teas, floribundas, grandifloras and many modern shrub roses are a tender flowering variety budded onto a tougher rootstock. The joint between them, the swollen knob at the base called the graft union, is the part that must stay alive. If a hard winter kills everything above the mound, a protected union can push new canes in spring. If the union freezes, the rootstock takes over and sends up its own growth, which usually carries small, plain flowers that have nothing to do with the rose you paid for.
Which roses can skip it?
Hardy roses growing on their own roots. Rugosas, most species roses and many of the Explorer and Parkland series bred for the Prairies tend to lose some cane tips and regrow from the crown, true to type, with snow acting as the blanket. In an exposed yard with little snow, a light mound still helps them. The question of which ones are tough enough has its own page, Roses That Hold Up in Manitoba. Here is the plain answer for the province: there is no reliably mild corner where a hybrid tea can skip protection, and even the sheltered yards of the Red River Valley sit in the same cold zone.
When to start, and what triggers it
The signal is the weather, and the calendar only gives a rough guide. Plan on late October to early November for most of southern Manitoba, and expect it to slip earlier in the north and on higher ground. The first fall frost at the Winnipeg airport station averages September 22, but that frost only nips tender growth. Mounding then would be a mistake, because a rose buried in warm soil keeps its sap moving and never settles into dormancy.
How do you know the freeze has arrived?
Look for a run of nights that drop well below freezing, with daytime highs that stay near or below freezing, for a week or more. The top of the soil should be stiffening, so that a trowel meets resistance an inch or two down. The leaves will have yellowed and dropped, or been blackened by frost, and the canes will look dormant rather than green and active. A single cold snap followed by a warm spell does not count. Prairie autumns often serve up a hard freeze in mid-October and then a stretch of mild days, and a rose that has been covered during that stretch can start to rot under the soil.
What should you do before the freeze?
Three things come first, and all of them help the rose slow down. Stop fertilizing and stop deadheading by late summer, because both nudge the plant to push soft new growth that frost will kill. Leave the last flowers to form hips. Then water deeply in a dry fall until the ground freezes, since a rose that goes into winter thirsty is more prone to cane desiccation.
Buy your mounding material early. Garden centers across the province clear out their bagged soil once the weather turns, and a bag frozen to the pallet is hard to break up. A stack of bags waiting by the back door lets you act the day the forecast calls for it, rather than the weekend after the ground has frozen solid.
How to mound, and how deep
The job is to bury the graft union, because the canes will take whatever winter delivers. Even a well-protected hybrid tea usually loses much of its upper growth, and that is normal. What matters is that the crown and the lowest few buds sit under a thick, dry, insulating layer, where the temperature stays far steadier than the air above.
What do you mound with?
Bagged topsoil, garden soil or a soil and compost blend, bought fresh. Digging soil from around the rose is a habit worth breaking. It strips cover from the shallow feeder roots right beside the crown, and it leaves a trench that fills with meltwater and freezes into an ice collar around the plant. Prairie garden soil is often heavy clay that holds water, and wet clay mounded against canes stays cold and soggy. Bagged material is looser, drains better, weighs less and brings no black spot spores from last summer’s leaves. Bring the soil from another part of the yard if you must, but not from the rose’s own bed.
How do you build the mound?
Clear every fallen leaf from the base first, since old rose foliage carries fungal disease through winter. Tie the canes together loosely with twine, and trim any that stick out far enough to whip in the wind and loosen the roots. Then bury the graft union under a mound of soil, shaped like a cone and pressed in gently with your hands. Fill any gaps so cold air has no pockets to settle in.
Once the mound has frozen and the cold is settled, add a loose layer of straw, shredded leaves or evergreen boughs over the top. This extra layer shades the soil from bright late-winter sun, which can thaw it on a south-facing bed and then let it refreeze. It also holds the snow where you want it, because snow is an excellent natural insulator for roses. Do not use whole leaves alone for the mound itself. They mat down into a wet blanket that stays soggy for weeks.
What does not work in this climate
Several well-meant habits can cause winter damage of their own. All of them make the same mistake, which is to trap warmth and moisture around a plant that needs to stay cold and dry.
Does plastic wrap protect roses?
No. Plastic sheeting or a bag pulled over the canes seals in humidity, and on a sunny day in February the air inside warms well above the temperature outside. The canes sweat, then freeze again when the sun drops. Canes that spend winter in a wet, still bag break dormancy early and often grow mold, while the crown stays unprotected from the real cold. Burlap or breathable fabric is a safer wrap than plastic, and is best used only as an outer layer over a mound.
Do rose cones work?
Foam rose cones were designed for milder places than the Prairies. A sealed cone is a small greenhouse. It warms up in bright winter sun, wakes the plant, and then the next hard night freezes the tissue that woke. Condensation inside also encourages rot, and a cone filled with leaves makes a cozy home for mice and voles that chew canes and bark. If you use one at all, put it on top of a soil mound and cut ventilation holes in the top so air and moisture can escape.
Is it a mistake to mulch early?
Piling straw, wood chips or leaves around a rose while the soil is still warm is a common one. The warm ground under that blanket stays active, fungi thrive in the damp, and voles move in before the cold arrives. The plant never hardens off properly. Wait for the soil to freeze, and apply organic cover only on top of the mound, not instead of it.
Checking this against your own area
Every date here follows the Winnipeg airport station, and Manitoba is a large province with a lot of variation. Higher ground such as the escarpment districts runs colder than the Red River Valley floor, and cold air also drains into low spots and hollows, so a garden at the bottom of a slope freezes earlier than one higher up. Before you fix a date, check your own frost dates with Manitoba Agriculture or your local Manitoba Agriculture office, and watch your own soil and the forecast rather than the calendar.
Common questions
Can I protect roses with fallen leaves instead of soil?
Leaves alone are a poor substitute. They pack down, hold water and freeze into a wet mat against the canes. They work as a top layer over a soil mound after the ground has frozen, when they help catch snow, but they do not replace the soil around the graft union.
How do I protect climbing roses?
Climbers are harder because their long canes cannot be mounded in place. Many Prairie gardeners untie the canes, lay them flat on the ground, and cover them with soil, straw or evergreen boughs once the freeze has set in. Cold-hardy climbers can sometimes stay on the trellis with some dieback, but a tender one left upright will usually lose its canes down to the snow line.
When do I take the mound off in spring?
Remove it in stages once the soil has thawed and the hardest frosts have passed. The Winnipeg airport station’s mean last spring frost is May 23, which means roughly half of all years bring a frost after that date. Take the top layer off first, then the soil over a few days, and keep some material nearby in case a cold night returns. The pruning step that follows is covered in When to Prune Roses in Manitoba.
Should I water roses before winter?
Yes, in a dry fall. A deep soaking until the ground freezes leaves the roots and canes better hydrated for winter, which reduces cane dieback from wind and cold. Stop once the soil is frozen, and do not water after the mound is in place.