Grafted roses such as hybrid teas and floribundas need winter protection in Newfoundland and Labrador. Many tough shrub roses growing on their own roots, in the milder coastal parts of the island, do not. The protection itself is simple. Once hard freezes have settled in, bury the base of the plant under about a foot of bagged soil and leave it alone until spring. Plastic wraps and sealed cones do more harm than good. Everything else about the plant is in growing roses in Newfoundland and Labrador.
Do roses need winter protection in Newfoundland and Labrador?
St. John’s, the reference city for the province, sits in Canadian hardiness zone 6a, according to Natural Resources Canada’s plant hardiness site. That is a Canadian rating and it does not convert to a USDA zone. The Canadian system weighs seven climate variables where the USDA system uses one, and Natural Resources Canada says plainly that there are no simple conversions between the two. Read on its own terms, Canadian zone 6a is a mild rating for the country. A rugged shrub rose on its own roots, in a sheltered yard near the coast, often comes through winter with no mounding at all.
The zone number leaves out what actually damages roses on the island. Winter swings between thaw, rain and refreeze, and wind off the water dries out exposed canes. A grafted rose is among the most vulnerable because its named variety is joined to a rootstock chosen for vigor. If the graft union freezes, the plant that regrows from below is the rootstock. That usually means a rangy rose with small, plain flowers, and not the one you paid for.
Which roses need mounding in Newfoundland and Labrador?
Plan on mounding every grafted rose. That includes hybrid teas, grandifloras, floribundas and many other nursery roses sold grafted. The tag or the grower will tell you which you have, and a grafted plant shows a swollen knuckle at the base of its canes. Own-root hardy shrub roses, rugosas among them, can usually stay as they are, though in an exposed yard they still lose cane tips to wind. Which ones are worth planting in the first place is covered in Roses That Hold Up in Newfoundland and Labrador.
Do roses in Labrador need winter protection?
Yes, and the answer is stronger there. Labrador lies far north of St. John’s, and Canadian zone 6a does not describe it. Winters are colder, snow arrives earlier and stays later, and anything tender needs full protection. Even hardy roses may die back to the snow line. Snow is excellent insulation, so canes above it take the damage while the buried base survives. Look up the rating for your own community on the Natural Resources Canada map before you choose plants.
When to start, and what triggers it
The trigger is a run of hard freezes, and the calendar only gives a rough window. At the St. John’s airport weather station, Environment and Climate Change Canada puts the average first fall frost at about October 15 to 17, depending on the reference period. That is a midpoint, so in roughly one year out of two the first frost arrives earlier, and in the other half it comes later.
A first frost is not the cue to mound. A rose often keeps leafing, and sometimes blooming, for weeks after it. Mound too early and you cover a plant that is still growing. Fresh soil over warm ground holds heat and moisture around the crown, and a rose that has not hardened off takes a deep freeze badly. Most years the right moment falls somewhere in late October through November, later along the mild coast and earlier on higher or more northern ground.
How do you know the freeze is hard enough?
Watch the plant and the ground, not the date. The leaves have yellowed and dropped or hang limp, new shoots have stopped, and several nights in a row have frozen hard. Then try this test. Push a trowel into the soil beside the rose in the morning. If the top layer is stiff, and still stiff by afternoon, the plant is dormant and the mound can go on. A few mild days in between do not cancel that.
What if snow comes before the ground freezes?
On the coast it happens. If snow lands first, wait for the ground to stiffen under it, then brush the snow off the base and mound. The practical trouble is the soil itself. Bagged soil left outdoors can freeze into a block and cannot be spread. Buy it in October, while garden centers still stock it, and keep the bags in a shed or garage until the day you need them.
How to mound, and how deep
What has to be buried is the graft union, the swollen knuckle at the base of the plant where the variety was joined to its rootstock. The canes are expendable. They may die back to the mound or the snow line, and spring pruning removes them. The union is what regrows the rose you chose. So the whole job comes down to one action: bury the graft union under 10 to 12 inches of loose soil, shaped into a cone around the base of the plant.
What should you mound roses with?
Use bagged topsoil or bagged garden soil. Soil dug from around the rose seems free and handy, but it causes three problems. Digging strips soil off the shallow roots and exposes the crown you are trying to cover. It leaves a trench that fills with meltwater and freezes into a ring of ice around the plant. And late-fall garden soil is usually wet and heavy, so it packs into clods that hold water against the canes. Bagged soil is loose and drains well. It has not spent the summer under a rose with leaf spot, and if the bags were stored dry it stays workable even when the ground outside has turned hard.
How do you mound a rose, step by step?
- Tie the canes loosely together with twine so wind cannot whip them against the base.
- Rake away fallen leaves and debris around the plant, since leaf spot overwinters there.
- Pour bagged soil over the base and between the canes until the mound stands 10 to 12 inches high, then pat it firm.
- Once the surface has frozen, lay spruce or fir boughs over the mound and canes. They catch snow and shade the canes from midwinter sun.
- In an exposed yard, stake a burlap screen on the windward side, set away from the canes.
Spruce and fir boughs are easy to come by on the island, and a snow layer caught by them protects better than a store-bought wrap.
What does not work in this climate
Three habits look protective and cause trouble where winter swings between thaw and freeze. The first is wrapping the plant in plastic. Plastic holds moisture in and lets none out. On a sunny day during a thaw, the air inside warms well above the air outside, the canes sweat, and gray mold takes hold on wet tissue. Then the temperature drops overnight and the soft, damp canes freeze. Burlap breathes. Plastic does not, and that is the whole difference.
Can you leave a rose cone on all winter?
A foam rose cone sealed at the top acts like the plastic: a small greenhouse over the plant, warm by afternoon and damp by morning. Thaw spells and winter sun wake the buds inside, and the soft new growth freezes when the cold returns. Light cones also tip over in coastal wind, and without soil underneath they add little insulation against a deep freeze. A cone can work as a cap over a soil mound, with the top left open on mild days. It cannot replace the mound.
The third habit is piling mulch, straw or leaves around the plant while the ground is still warm. Warm soil under a thick blanket stays active and wet at the crown, which invites rot. The pile also gives voles and mice a sheltered place to spend the winter, and they chew the bark at the base of the canes. Wait until the ground surface has frozen before covering anything. After that, the cover keeps the soil frozen through midwinter thaws instead of letting it swing up and down.
Checking this against your own community
The frost dates and the Canadian zone above describe St. John’s. Newfoundland and Labrador has no counties, so the unit that matters is your own community and your own site. Higher ground, inland barrens, exposed headlands and northern districts run colder, and their frost dates fall weeks away from the airport’s. Compare your yard’s elevation and exposure with the airport’s before you settle on a mounding date. For regional advice, contact the provincial Department of Forestry, Agriculture and Lands, and look up your municipality on the Natural Resources Canada hardiness map.
Common questions
Short answers to what comes up once the mound is built.
When should you remove the mound in spring?
Take it off in stages as the soil thaws and the buds begin to swell. Lift the boughs first, then draw the soil down until the graft union is exposed. The airport station’s average last spring frost falls around May 30 to June 1, and in about half of all years it comes later, so keep soil and boughs close by in case of a cold snap.
Should you prune roses before mounding them?
Only enough to stop wind damage. Tie up canes, and shorten any tall enough to whip around. Save the real pruning for spring, when you can see which wood is alive. The timing is covered in When to Prune Roses in Newfoundland and Labrador.
Do climbing roses need protection?
Hardy climbers can usually stay on their supports, though the tips may die back. Tender or grafted climbers are better untied after the leaves drop, bent gently down along the ground, pinned, and covered with soil and boughs. The graft union still gets its own mound. Bend the canes a little at a time, because stiff wood snaps.
Do potted roses need different winter care?
Yes. Roots in a container freeze harder than roots in the ground, and a mound cannot fix that. Once the plant is dormant, move the pot into an unheated garage or shed. Water lightly now and then so the root ball does not dry out. Another option is to sink the pot into a garden bed and mound over it like any other rose.