Thank you for reading my question. I want to put a climbing rose on the corner of my deck. For that I will have to build a small raised bed (bottomless) that comes from the ground level upto the level of the deck ( 2 feet high ). So if I put a rose ( alchemist) in the 2 x 2 raised bed, will it survive the winter? will the soil stay warm enough?
Thank you for contacting the Toronto Master Gardeners.
The ‘Alchemist’ climbing rose grafted onto the Rosa Multiflora rootstock produces beautiful apricot/pink fragrant flowers. You can expect this climber to grow to 8-10’.
When selecting a container for growing roses, the size of the container matters, the larger the better. Roses have extensive root systems. The container should be big enough to accommodate the root ball of the plant, plus offer room for growth. A large container also holds more soil volume and dries out less frequently than a smaller pot, which means less watering for you and more insulating factor for overwintering. Good drainage is another essential factor to consider. If the soil is too wet, the roots will rot. Make sure your container has adequate drainage.
The hardest part about overwintering any plant in a pot is the freeze-thaw cycle that happens when water in the container soil constantly melts and refreezes in the winter sunshine. This can cause the soil to become dry and be damaging to the roots, and root health is crucial to successful container gardening. Be sure to water the container well before the soil freezes. The container must be both large and well insulated, using something like styrofoam sheeting. You can also insulate the container by piling compost, straw, mulch or leaves on top of the soil, and by placing garbage bags full of leaves around the container.
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.
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 do not mention where you are located in Toronto. There is no exact science for predicting how long roses grown in a container will survive. Each winter brings a new set of challenges.
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.
Below is a link from our library which answers your questions.
www.torontomastergardeners.ca/askagardener/growing-roses-in-container
Here are some more links for further research.
www.provenwinners.com/overwintering-perennials-shrubs
https://www.midwestgardentips.com/container_roses.html
Container Rose Gardening Made Easy