Though most "last frost" charts report dates in April for my area, gardeners I know wait until more like mid May, or Mother's Day as a rule of thumb. While the weather warms pretty early most years, we can and do get very late frosts. Like Dave, I start watching the weather forecast around that time, and I don't plant them out until it looks like smooth sailing.
In recent years I've been wintersowing my tomatoes, so they tend to still be very small when they're transplanted into the garden. They show very little above ground growth during those cooler, early spring days, but they have amazing root systems. This is May 2012, after transplant.
This is those same plants in August
I'll never start my tomato seeds under lights anymore, it's wintersown all the way for me.
Karen
