When I was young, the farmers had a test for whether their corn crop would be good. The saying, "Knee-high by the fourth of July" meant that if their corn was knee-high by then, the crop was likely to be a good one. Of course, it was just a vague rule of thumb, since corn matures much more quickly farther south than it does in the northern states or in Canada.
This summer, it looks to us as if the corn in our area is about waist-high on the fourth of July. We have had some good warm stretches and lots of moisture. The farmers around here are working very hard to find something about the weather to complain about... 8-)