We are looking to plant a flowering tree here at our condo complex in Scarborough, Ontario.. The site is partially over our underground garage roof with a depth of no more than 3 feet so roots must be more spreading than tap. We had all the landscaping removed 4 years ago in order to do a full waterproofing of the garage roof so I expect that the soil that was replaced was topsoil. There are other places on the property where we do have Scarborough clay under the grass topsoil. The site is in full sun all day but not particularly protected. We are looking for something with spring colour but not a huge tree. I had looked at the eastern redbud until I discovered it was prone to webworm. I have dealt with this problem before and in our re-landscaping of the property have worked to avoid trees that are prone to this issue. As stated, we are looking for something with spring colour, clean and low maintenance. Any suggestions would be appreciated.
Susan Montreuil
Thank you for contacting Toronto Master Gardeners. A wide variety of trees could fit into the site you describe. Under Canadian Nursery Stock Standards, trees grown in containers, or balled & burlap, will have fibrous roots because they must be root-pruned in the nursery to adapt to a small space. Even small trees may reach 10-15 ft. You might also consider a bush form of a tree, or a bush grown on a standard. The Redbud is in the Rosaceae family, and so like roses it is prone to some diseases. The fall webworm, native to North America, attacks many hardwood trees and is also found in Europe. It is important to check disease resistance for any tree you consider. The key to growing the tree successfully, when the soil is not very deep, is to have a watering system that keeps the soil moist and drains away from the garage roof underneath.
Before you plant the tree, the soil should be amended, even if it is topsoil, to give it the best chance of survival. A garden soil containing compost should be placed in the area where the tree is to be planted. You should expect the tree root area to extend at least two feet in every direction. The soil must settle well before you plant the tree. The tree trunk must not be buried so the hole, when dug, should be no bigger than the container the tree comes in. Ideally, buy from a nursery that offers a one-year guarantee.
The Sweetbay Magnolia, and cultivars, are native to Eastern North America. It is disease-resistant but likes to be wet. It is found in a shrub and a small tree (15 ft) form. One can be seen at the Toronto Botanical Garden. The flowers are cream-coloured. Also, the Star Magnolia should be considered. It blooms very early with delicate white flowers, and like the Sweetbay, is disease resistant. Crab-apple species might also be considered, but disease resistance varies greatly among cultivars. They are also in the Rosaceae family. Among the dogwoods, the native Pagoda Dogwood has attractive white flowers in the spring and turns a brilliant burgundy in the fall. It tends to be wider than it is tall. It is very disease-resistant. Japanese maples are beautiful, but they do best in partial shade and require a lot of water. They are susceptible to several serious diseases depending on the cultivar. Finally, the Serviceberry should be considered. It is a small tree, or multi-branched shrub, native to our region. It blooms in May before it or any other trees have fully leafed out. In fall it turns orange-red. The cultivar ‘Prince William’ is a large shrub with good fall color. More information on small trees can be found on the Morton Arboretum site.