Growing roses in containers

(Question)

I read in the Q&A that with proper protection, roses can survive Toronto’s winter. My home is at Leslie and south of Steele. However when I bought 8 floribundas roses from Sheridan garden, the advice is it will not survive even with protection. Bringing containers back to garage is not an option.
Regarding planting of roses, I read in cold weather like Toronto to plant with bud union 3 inches below surface. Sheridan said to plant bud Union just below surface.
Looking forward to your response soonest possible. Thank you

(Answer)

Thank you for contacting the Toronto Master Gardeners.

Different types of roses possess various levels of winter hardiness, and sadly not all of them are winter hardy in Toronto. The rule of thumb for Toronto’s hardiness zone is: zone 6a south of the 401 and zone 5B north of the 401. Then you need to subtract one full zone to account for the fact that the insulating properties of soil are greatly reduced when a plant is grown in a container. Therefore, to find roses that would reliably overwinter in a container in your north of 401 garden, you should choose from ones that are hardy to Canadian hardiness zone 4.

Unfortunately the hybrid tea and floribunda roses, and any rose that has significant hybrid tea and/or floribunda parentage, are generally hardy only to zone 5 or 6 and will not survive in a pot in our winters. When you are shopping for roses and reading the plant labels, keep in mind that the hardiness zones listed are almost always USDA zones; to arrive at a rough Canadian equivalent, add one zone. You still have many beautiful roses to choose from; to get you started, here is a few of the more compact varieties of roses hardy to zone 4:

  • ‘Campfire’
  • ‘Champlain’
  • ‘Cuthbert Grant’ (and almost everything from the Canadian Parkland series!)
  • ‘Marie Bugnet’
  • ‘Parfum de l’Hay’
  • ‘The Fairy’

The most tender part of a grafted rose is the bud union; you want to make sure that this part survives the winter so that even if everything is killed back to the soil line, the rose can generate new canes from the grafted stock and not from the root stock. Therefore in cold climates it is advisable to situate the bud union at least 3 inches below the soil line, to take full advantage of the insulating properties of soil. However, if you are planning to culture the rose in a container, the entire plant will need winter protection anyway and the depth of the bud union is unlikely to make a difference. In fact, some rosarians argue that leaving the bud union exposed will help promote new basal growth.

Good luck!