I live in Zone 6a to 7a Toronto new Lake Ontario.
The soil is largely clay we added topsoil and regularly add compost.
I would like to plant an evergreen tree in an area that gets full sun 4 hours a day then is shaded.
I would like to plant this tree near a cement block garage
I would like a mini white pine but I understand it does not tolerate clay soil. Can you recommend an evergreen for this spot
P.S. I would prefer to plant a Canadian species.
Thank you for contacting the Toronto Master Gardeners with your inquiry.
Working with clay soil requires persistence, dedication and time. The problem with clay is that the particles (aggregates) are small and fit together fairly tightly leaving very little space between for drainage or oxygen. Because of the lack of oxygen and drainage the plants have difficulty absorbing nutrients and attaining the amount of oxygen they need to function properly. By slowly incorporating compost into the top few inches every year, which you are currently doing, will allow the clay to slowly loosen up.
Many coniferous trees require excellent drainage and full sun (6 hrs sunlight), but there are a few varieties which tolerate clay soil and part shade (3-6 hrs). Without knowing the size of your planting area it is difficult to suggest one specific plant, however below is a link to one of our earlier posts which lists evergreens of various size that are tolerant of shade and clay soil:
Another evergreen to consider is Thuja occidentalis ‘Degroot’s Spire’, a dwarf, slow-growing, evergreen shrub with an upright, pyramidal habit which thrives in full sun ( 6 hours of direct sunlight), however it will tolerate partial shade (3-6 hours of morning or early afternoon sun). At maturity this type of cedar will grow to be about 12 feet tall, with a spread of 3 feet within 15-20 years. This cedar prefers moist, well-drained soil but it tolerates clay soil.
Also, you might be interested in the following links to Toronto Master Gardener Fact Sheets on Improving your Soil Organically, Compost for your Organic Garden, and Growing Trees and Shrubs Organically, which you may find helpful.