Grafted roses in New Brunswick need winter protection, and the job is short: bury the base of the plant under loose, bagged soil once a run of hard freezes has shut the plant down. Hardy own-root shrub roses usually get by on snow alone. Timing is easy to get wrong. Cover too early and the plant keeps growing. Cover with the wrong material and it rots.
Do roses need winter protection in New Brunswick?
It depends on how the rose was made. The reference city of Moncton sits in Canadian plant hardiness zone 5 (5a or 5b depending on the map edition and the exact spot), according to Natural Resources Canada’s plant hardiness map. Cold snaps there can sink below zero Fahrenheit, and a rose bred for a milder region will lose canes, or the whole top, in that kind of weather. Hybrid teas, grandifloras, floribundas, and most grafted garden roses fall into that group. They need cover every year.
One caution on the number itself. The Canadian system is built on seven climate variables, while the USDA system uses one, so a Canadian zone 5 does not convert to a USDA zone. Use it as it stands, and compare it only with other Canadian zone ratings.
Hardy roses are a different story. Rugosas, many Canadian-bred shrub roses, and many own-root roses grow from a root system that can regrow even if the canes die back. In the milder pockets of the province, such as sheltered spots near the Bay of Fundy, these roses need no mounding at all. A reliable blanket of snow does most of the work for them. For those plants the honest answer is no, and you can skip the soil bags. Picking roses suited to the climate is a separate question, covered under rose varieties for New Brunswick.
Cold alone is rarely what kills a rose here. The bigger threats are a midwinter thaw followed by a hard freeze, drying wind on exposed canes, and late-winter sun that wakes the buds before the soil has thawed. Snow insulates against all three, which is why a rose in a wind-scoured front bed often suffers more than one tucked beside a house or fence where drifts pile up. If your bed is open and windy, treat even a moderately hardy rose as one that needs protection.
For a broader look at the plant itself, see our guide to growing roses in New Brunswick. What follows covers only the cold months.
When to start, and what triggers it
Start after a run of hard freezes, not on a set date. A rose needs real cold to go dormant, and a mound built in mild weather keeps the soil warm enough for the plant to stay active. That means soft new growth, which a deep freeze then kills. A frost that blackens the leaves is only the first signal, since the plant is still alive underneath.
The mean first fall frost at the Moncton station is October 2, so in half of years the first frost comes earlier and in half it comes later. The hard freezes that matter come several weeks after that. Around Moncton, plan to mound in late October into November. Colder, higher districts get there sooner, and the coast tends to run later. Judge by the weather, because the calendar only tells you when to start watching.
Three signs tell you the plant is ready:
- Most of the leaves have yellowed and dropped, and no new shoots are forming.
- Several nights in a row have frozen hard, with the surface of the soil stiff in the morning.
- The forecast shows daytime highs staying close to freezing, not swinging back into the 50s.
Use the weeks before that to get ready. Buy bagged soil in September, while garden centers are well stocked, and stack it near the beds. Stop deadheading in late summer so the plant sets hips, which helps signal that growth should slow. Skip heavy pruning in fall, because cuts invite new growth at the wrong time. The right time to prune comes in spring, and When to Prune Roses in New Brunswick explains how to read the buds.
How to mound, and how deep
What you are protecting is the graft union, the knobby swelling at the base of the plant where the cultivated rose joins its rootstock. Canes can die back and regrow from that point, but if the union freezes, the plant is usually lost. So the job is to bury the graft union under a mound of loose soil about 10 to 12 inches deep, and the canes matter far less than that.
What should you mound with?
Use bagged topsoil, garden soil, or a compost-and-soil blend. Bring it to the plant, rather than digging beside it. Pile it up around the base in a cone, working it between the canes so no pockets of air are left near the crown. Before you start, tie the canes loosely together so they stand upright, and trim only the tallest ones that would whip around in winter wind. Leave the rest of the cutting for spring.
Once the mound has frozen, some gardeners add a loose layer of evergreen boughs or straw over the top. This helps catch snow and shades the soil from late-winter sun, but it is a bonus and not a replacement for the soil itself.
Why is bagged soil better than soil from around the plant?
Digging soil from beside the rose strips away the ground over the shallow feeder roots and exposes them to frost. It also leaves a trench around the plant where water collects and freezes. Soil from around a rose also carries whatever disease spores have built up in that bed over the season. Bagged soil is clean, loose, and usually drier, which makes it a better insulator. It also keeps the mound from packing into a dense, wet mass that holds cold against the crown.
When do you take the mound off?
Remove it gradually in spring, starting in April once the ground has thawed and the buds begin to swell. Pull away the top layer first, then the rest over a week or two, so the plant is not shocked by sudden sun and wind. The mean last spring frost at Moncton is May 23, which means frost arrives after that date in half of years. Keep a bedsheet or an upturned pail ready for a cold night after the mound is off, and spread the leftover soil around the bed.
What does not work in this climate
Plastic wrap looks protective and does the opposite. On a sunny day, even in winter, the air inside a plastic sleeve heats up and the canes sweat. That moisture stays trapped. Mold grows on the stems, and when the temperature drops again the damp wood freezes. The plant also gets a false signal to wake up. Burlap wrapped loosely around a frame of stakes breathes, and plastic does not.
Rose cones, the foam or plastic domes sold in fall, work only if they are managed. A sealed cone behaves like a small greenhouse on a sunny March day, with temperatures that climb and humidity that rots the canes. Those same cones are also warm, dry nests for mice and voles. If you use one, fill it with soil first, cut vent holes, and open or lift it on mild days so air can move. Most gardeners here will get better results from a mound of soil with nothing sealed over it.
Mulch piled around the base while the ground is still warm causes a quieter problem. The layer holds heat in the soil, so the plant keeps growing well into the cold season. It also gives rodents a cozy place to settle before winter and a convenient supply of bark to chew. Wait until the soil has begun to freeze before piling anything, and use a mulch that sheds water, such as evergreen boughs or straw, rather than wet shredded leaves that pack down into a soggy mat.
Burying the whole plant in leaves has the same drawback. Leaves hold water and mat down, and in a New Brunswick spring that mat stays wet and cold long after the snow has gone. Whatever you use, a dry, loose, well-drained cover will protect the plant, and a wet, airtight one will rot it.
Checking this against your own county
The Moncton figures are a reference point. A province is not one climate, and northern and upland districts run weeks behind the Moncton frost dates, with hard freezes arriving earlier in fall and the thaw coming later in spring. A few hundred feet of elevation can shift your timing, as can a low spot where cold air pools. Write down the date of the first hard freeze each fall and the date the soil thaws each spring, and your own record will soon beat any average. For local advice, contact the provincial agriculture department or start with Agriculture and Agri-Food Canada.
Common questions
Can I use fallen leaves to mound my roses?
Leaves alone are a poor choice, because they mat down and stay wet. They work better as a loose top layer over a soil mound, ideally mixed with evergreen boughs so air still moves through them.
Do climbing roses need the same protection?
Hardy climbers often survive on snow cover. Tender climbers need the base mounded like any other rose, and the canes can be unfastened, laid along the ground, and covered with soil or boughs. Check each cane for flexibility first, because a cold cane snaps easily.
Should I water roses before the ground freezes?
If fall has been dry, give the bed a deep watering before the soil freezes. Moist soil holds heat longer than dry soil and helps the roots through winter. Stop once the ground is frozen.
What about roses in pots?
Roots in a pot are exposed on all sides and freeze much harder than roots in the ground. Move the pot to an unheated garage or shed once the plant is dormant, water it lightly now and then so the soil does not dry out completely, and bring it back outside in spring when the worst of the cold has passed.