I heard delphiniums are challenging plants to grow and I am a little put off by the suggestion that they might not last longer than 2-3 years. How long do they usually live in Toronto?
Delphiniums have a reputation for being rather short-lived plants because they lose vigor after about 3-5 years, but that is not to say they can’t live longer and indeed many do. There are a few things you can do to ensure they stay as healthy as possible for as long as possible. First, be sure to plant them in rich, moist but well-drained soil. Add generous amounts of organic matter such as compost or well-rotted manure when preparing the planting hole, and give them lots of space to encourage air circulation and reduce the chances for disease. Delphiniums prefer summers on the cooler side so, if you live in Toronto, consider planting them in a location that receives some afternoon shade. When you notice a plant becoming overgrown after about 3 years, divide it in early spring just as new growth is emerging to help rejuvenate it and keep it happy for many more years to come (you can give some of the divisions away to friends/neighbours or add them to other parts of your garden).
Here are a few websites that might be of interest: Growing Delphiniums in the Home Garden , Plant Care Guide