Our oldest son is taking "corn" for one of his 4-H projects this year. While this might seem like the lamest project ever, we are really getting into it! He had to examine a seed corn bag's tag to learn about what's actually in the bag and the science behind the corn seeds. He conducted a germination experiment and has plans to do a soil "tilth" experiment, as well. He also learned about "growing degree days", which is a unit that measures how much heat the corn is exposed to over the growing season. Some varieties of corn require more degree days than others, but on average most corn varieties in Illinois require 2,300 to 2,700 growing degree days.
To figure out how many "growing degree days" each actual day is worth, use this formula:
high temp. + low temp. - 50
Some restrictions apply, though: if the daily high temp. is over 86, then only use 86, and likewise, if the low temp is below 50, then only use 50. This takes into account the stress on the plants on super-hot or unseasonably-cool days.
For example, Thursday's high temp. is forecasted to be 95 and the low temp. is forecasted to be 74.
That means that 86 + 74 = 160 /2 = 80 - 50 = 30 growing degree days on Thursday.
Now, if only it would rain...