Toronto gardening all year round: Markham

Useful websites

Geranium robertianum

Andy's Northern Ontario Wildflowers: a lot of them grow down here too! Includes shrubs, moss, fungi, and ferns as well as flowers.
Dave's Garden: a large, active online community. Be sure to check out their PlantFiles, a vast database with valuable information about thousands of different species and their cultivars.
Invasive Exotic Species Ranking for Southern Ontario (PDF): a must read for every gardener in Toronto.
Lady Bird Johnson Wildflower Center: although based in Texas, has a wealth of information about native plants from throughout Canada and the US
North American Native Plant Society: information about native plant gardening, plant sources, seed exchange
Plant Hardiness Data from Natural Resources Canada. Detailed maps for each plant showing where it grows (Canada and the United States only)
PLANTS Database from USDA. Great photos and illustrations about plants, as well as maps (Canada and the US only) showing in which states/provinces each species is found and in which it is native
Planting the Seed (PDF): A Guide to Establishing Prairie and Meadow Communities in Southern Ontario, from Environment Canada.
Plants for a Future: interesting website with information on the uses and care of 7000 plants, as well as information on permaculture and vegan organic gardening.