The magical safest-ever rule of gardening is to plant your garden after the May 24 weekend. But if you like to live a bit dangerously or if you can handle the small risk of frost a few weeks earlier against the possibility of extending your growing season, consider reading up on the average frost-free date for your region. This website shows the average frost free dates for cities all over Canada. It says here that Burlington's frost-free growing season, on average, is from May 5 to Oct 8th. I am not bad-girl enough to sow my delicate seedlings as early as May 5th, but perhaps the following weekend....
Whatever magical frost-free date you choose, after that you can plant your frost-sensitive plants. These are the ones that are generally seedlings when they go into the ground. If this is one of your first years of gardening, I recommend buying seedlings instead of trying to start them yourself. The crops that I put in after Mother's day include:
-green beans and yellow beans (these are seeds sown as seeds)
-zucchini and other squash
Zucchini plants take up LOTS of space. I didn't realize this the one year I put them in my garden and their gigantic leaves spread out and probably shaded out a square metre of garden.
Cucumber plants like to climb. I planted them near the chicken wire fence and let them climb up that.
Jalapeno plants produce lots of fruit (I'd guess 8-10 per plant). One year I planted six plants. I've found that too many peppers for our family, so now I try to just buy one or two.
~Miss Greenish Thumb~