Hello,
I would like to plant a tree in a very large container on my patio. It’s not possible to plant it in the ground there. I am hoping to be able to grow it tall to extend above our fence to provide privacy. I’m in zone 5b so of course winter protection with the roots above ground would be a concern. I am hoping that something would grow 8-10 feet tall? Is this at all possible? What tree should I get and how large and deep should the container be?
Thanks!
Thanks for contacting Toronto Master Gardeners! Growing trees in containers can be tricky, but it’s definitely possible. You’ve already identified some factors to consider, such as your growing zone, winter protection, and size/depth of container. Let’s touch on those factors, along with a few others.
Tree Selection: A good rule of thumb for growing any plants in containers is to select plants that are hardy to zones *lower* than yours, since their roots will remain above ground and exposed to colder temperatures than if they were grown in-ground. In your case, you’ll want to select a tree species that is hardy to zone 3 or 4. Here is a list of understory trees that would be ideal candidates. Not only do they tick the hardiness box but they also tend to grow smaller than other trees and will be better suited to growing in a container.
Soil: Opt for a high-quality potting soil, which is specially designed for growing in containers and will provide better drainage and moisture retention than other soil mixes.
Container Selection: Get the largest, durable pot you can find. It should be, at the very least, twice as wide and deep as the tree’s root ball. Specialty garden centres or tree nurseries will be your best bet for finding extra (extra!) large pots that are manufactured to last outdoors for many years and can withstand freeze-thaw cycles without cracking. The larger the pot, the heavier it will also be, and the less likely you will have to worry about wind and other extreme weather blowing the tree over.
Watering and Fertilizing: A container-bound tree will require more water than a tree grown in-ground, as the soil will dry out faster. During summer months, be sure to check the container regularly and water when the top two inches of soil feel dry. Add a slow-release granular fertilizer specifically formulated for trees and shrubs, being sure to follow the manufacturer’s instructions. This is typically done in spring, but may also be needed later in the season depending on the type of tree you decide to grow.
Winter Protection: This ties into tree selection. By choosing a tree that is hardy to zones 3 or 4, it will be more likely to survive winter in a container. Additional strategies can be used to offer further winter protection, such as wrapping the container in a thermal covering or bubble wrap, or moving it to an unheated garage, if that is feasible.
For a more complete rundown on growing in containers, please check out our Container Gardening guide.
You may also find this previous post about trees and shrubs for a rooftop terrace helpful.
April 26, 2024