Overwintering Roses: Protecting the Graft and the Canes

Preparation starts in late summer

Winter survival is mostly decided before winter arrives. A rose that is still pushing soft, sappy shoots when the first frost comes will lose them, and the dieback can run some way down the cane. The way to avoid that is to stop feeding nitrogen roughly eight weeks before your first expected frost so the wood has time to ripen and harden.

The second signal is deadheading. Stop it in early autumn on any rose that sets hips, and let the fruit form. A plant that is ripening seed slows its growth down of its own accord, which is exactly what you want going into the cold.

Do not do the main prune in autumn. Every cut is an open wound going into the cold, and you cannot yet tell which wood will come through. Cut properly in late winter instead.

The graft union is the part to protect

Most bush roses are grafted, and the swollen knuckle where the cultivar joins the rootstock is the least hardy part of the plant. Lose the top growth and it regrows; lose the graft union and everything above it dies, and what comes back is the rootstock, which is a different rose entirely.

In a mild garden the union can sit at soil level and needs nothing. In a cold one, mound loose soil or compost eight to twelve inches (20 to 30 cm) over the base after the ground has cooled, which insulates the union against the freeze and thaw cycles that do the damage. Bring the mounding material from elsewhere rather than scraping it from around the roots.

1. Wait until the ground has cooled Mound after a couple of hard frosts, not at the first cold snap. Mounding while the soil is still warm keeps the plant active and invites rot at the base.
2. Use loose, free draining material Soil, compost or bark from elsewhere in the garden. Anything that packs down wet and stays wet against the stems causes the rot you are trying to prevent.
3. Cover the union fully Aim for a mound that puts 8 to 12 in (20 to 30 cm) of material over the knuckle. Partial cover protects nothing.
4. Remove it gradually in spring Pull the mound away in stages as the hard frosts end. Removing it all on the first warm day exposes tissue that has spent months insulated.
5. Check the height afterwards Heavy winter rain washes mounds away and can leave the union bare. Look again midwinter and top it up if needed.

Roses grown on their own roots have no union to lose. If the top is killed they resprout as themselves, which is why own root plants are worth seeking out in the coldest gardens.

Roses in containers need more protection

A rose in the ground has the whole mass of the soil buffering its roots. The same rose in a pot has a few gallons of compost that freezes solid from all sides, and frozen compost means the plant cannot take up water even while cold wind pulls moisture out of the canes. Container roses are lost to winter far more often than roses in beds.

Move pots against a house wall or under an overhang, group them together so they insulate each other, and wrap the sides of the pot rather than the plant. Water occasionally on mild days: a dormant rose still drinks a little, and a pot that dries out completely over winter is as damaging as one that freezes.

Wrap the pot, not the plant. Wrapping the canes traps damp against them and causes more rot than the cold would have caused dieback.

Reading winter damage in spring

Some cane damage every winter is normal and not a problem. Blackened or shriveled tips are cut off at the late winter prune and the plant carries on. What matters is how far down the damage goes, and the way to find out is to cut and look at the pith in the middle of the cut face.

White pith means live wood; brown or gray pith means the cane is dead at that height and you keep cutting lower. Work down cane by cane until every cut face is clean. If you reach the base and the pith is still brown, that cane goes out entirely.

Be patient before writing a rose off. Growth can be several weeks late after a hard winter, and a plant with no visible buds in early spring is often still alive. Scrape a little bark with a thumbnail: green underneath means wait.

Getting the timing right at both ends

The two mistakes that cost roses over winter are protecting too early and unprotecting too late. Mounding or wrapping while the soil is still warm keeps the plant growing when it should be shutting down, and leaving the covering on into a mild spring cooks the new growth and holds damp around the base just when the plant needs to dry out and breathe.

Take the protection off in stages as the hard frosts finish and before the buds break, then do the main prune. Record the date you mounded, the date you uncovered, and how much dieback you found. After two winters those notes tell you whether your protection is doing anything at all, or whether your garden simply never needed it.