A Canadian winter does not kill plants with cold alone. It kills them with freeze-thaw cycles that heave roots out of the ground, drying winds that desiccate evergreens, rodents that chew bark under the snow, and wet crowns that rot. A little work before freeze-up protects your perennials, roses, and shrubs from all four. Here is what to do, and how much of it you actually need depending on where in Canada you garden.
First rule: wait until the plants are dormant
The most common mistake is protecting plants too early. Mulch and covers go on after the ground has started to freeze and the plants have gone dormant, not at the first chill. Cover too soon and you keep the soil warm, which delays dormancy, invites rot, and builds a cozy hotel for mice. The point of winter mulch is to keep plants consistently cold and stop the soil from thawing and refreezing, not to keep them warm.
Perennials
- Leave healthy stems standing where you can. Hollow stems shelter native bees, seed heads feed birds, and standing stems catch insulating snow. Cut back only what was diseased or mushy. (More on this in our fall cleanup guide.)
- Mulch the crowns after freeze-up with 3 to 4 inches of shredded leaves or straw, more for anything new or borderline-hardy for your zone.
- Water deeply before the ground freezes if fall has been dry. A hydrated plant going into winter is far more resilient than a thirsty one.
- Watch for heaving. New fall plantings are most at risk of being pushed out of the soil by freeze-thaw. Mulch holds them in place; if one heaves in a thaw, press it back down.
Roses
How much roses need depends entirely on the type. Hardy shrub roses bred for this climate, the Canadian Explorer and Parkland series, Rugosas, and most old garden roses, need almost nothing beyond a mulch. Tender hybrid teas, floribundas, and grafted roses need real protection in cold zones.
- Stop deadheading in late summer and let the last blooms form hips. This signals the plant to harden off instead of pushing tender new growth.
- Do not prune hard in fall. Shorten only the longest canes to stop wind-rock, and save real pruning for spring.
- Protect the graft union. After dormancy, mound 8 to 12 inches of soil or compost over the base of tender grafted roses. In the coldest zones, add a collar of leaves held by burlap or a rose cone with a ventilation hole on top.
Shrubs and evergreens
- Shield evergreens from wind and winter sun. Cedars, boxwood, and young conifers brown out when winter wind and bright sun pull moisture from needles the frozen roots cannot replace. A burlap screen on the windward and south sides helps most, especially for the first few winters and in exposed spots.
- Water evergreens well before freeze-up. They lose moisture all winter, so they go into it fully hydrated.
- Prevent snow-load splitting on multi-stem shrubs and columnar cedars by loosely tying the stems together with soft twine.
- Potted shrubs are a separate problem. Roots in a pot sit at air temperature and freeze far more easily than in the ground. Heel the pot into a bed or move it to cold storage, the same approach as our potted grape vine guide.
Keep the rodents off
Mice, voles, and rabbits chew bark at the base of roses, shrubs, and young trees under the cover of snow, and a fully girdled stem dies. Wrap trunks with a spiral tree guard or a cylinder of hardware cloth pushed an inch into the soil, and keep mulch pulled back a couple of inches from the bark so you are not building nesting cover right against the stem.
How much by zone
- Zones 2 to 4 (Prairies, the North, cold interior): the full treatment. Reliable snow is your best insulation, so mulch crowns, protect tender roses and young evergreens, and guard against rodents. Stick to plants rated at least a zone hardier than you for anything you want to survive without fuss.
- Zones 5 to 6 (much of Ontario, Quebec, the Maritimes): mulch after freeze-up, protect grafted roses and exposed evergreens, and you are in good shape.
- Zones 7 to 8 (coastal BC): winter is mild enough that a mulch and some wind protection for evergreens is usually all it takes. The bigger risk is wet, so make sure crowns are not sitting in soggy ground.
Two things not to do
- Do not fertilize in fall. It pushes tender new growth that winter kills. Feed in spring instead.
- Do not mulch before the ground freezes. Early mulch keeps the soil warm and invites rot and rodents. Wait for the cold to settle in, then tuck everything in.
Not sure when your ground will start to lock up? Your local first-frost date is a good signal that dormancy and freeze-up are close. Do this work in the short window after that, and your garden comes back in spring instead of greeting you with a row of dead roses.