Hello: I just moved to a typical downtown row house in Parkdale, Toronto. As the lot runs east-west, we have lots of sunlight in the backyard most of the day. The soil is loam and clay, but we can work on it. I really want a fine tall conifer in one corner, and have visited a house not far away growing a beautiful and huge Eastern White Pine. Should I try? Maybe dig out the area and give it more sand? Or will the pollution from the nearby Gardiner cause it grief? What other conifers, prefer native, could I try? Thanks!
For your backyard, which has clay-loam soil and is close to a source of air pollution, eastern white pine (Pinus strobus) is not an ideal choice, but it may be possible to make it work. Eastern white pine can tolerate a fairly wide range of soils; best growth occurs in moist, well-drained, sandy loam that is mildly acidic (pH level about 5.5). It can decline quickly if it is grown in clay, wet, or alkaline soils; it will suffer from chlorosis and eventually die if the soil pH reaches above 7. Its roots also have a strong affinity for a specific soil mycorrhizae. Moreover, it is sensitive to air pollution, and is not tolerant of salt.
You can improve the drainage of your soil simply by adding organic materials like compost or well-rotted manure; this will improve the structure of the soil. It is not practical to try to change the texture of a soil; no matter how much sand you add, the soil will eventually revert to its original clay loam texture. As for soil pH, do not attempt to adjust it until you have a proper soil test done at a reputable laboratory; the test result will include instructions on what type and how much amendment to add to achieve the level of acidity you need. Source your tree from a reputable nursery specializing in native plants, where it is more likely that the trees are pruned properly and grown in soil with the mycorrhizae already present.
Two native evergreen trees that are better suited to the soil condition of your backyard are the white spruce (Picea glauca) and eastern white cedar (Thuja occidentalis).
No matter what tree you choose in the end, it is vital that it is planted properly; even a healthy tree ideally suited to your location, receiving all the TLC you can give, will suffer and even die if it were incorrectly planted. For more information, please see Planting a Tree: A Toronto Master Gardeners Guide.
We wish you the best of luck with your new evergreen tree.