Knee high by the 4th of July? 

Phooey! 

Most sweet corn varieties take 75 to 85 days to harvest. Corn maturity time is actually based on "growing degree days" so warmer weather will result in earlier maturity and cooler weather, well, you know... 

Figuring 85 days to maturity, if you live in a zone where the first frost date is likely to be the middle of September (e.g. Minnesota), you can probably plant sweet corn as late as the third week of June.

Early October first frost (e.g. Iowa) plant as late as early July.

Mid-October first frost (e.g. central and south Missouri) plant as late as mid-July.

Early November first frost (e.g. south Arkansas) plant as late as mid-August.

That's all GREAT NEWS, because once you find out how much easier it is to process your sweet corn harvest with the Corn Kernel Cutter, you will want to plant more corn than ever!