You can also isolate corn crops by maturity or time. For instance, if the types of corn have maturity dates that are at least seven days apart, you can plant them close together, as when one variety is shedding pollen, the other type won't be receptive. Isolating by time is a matter of spacing your plantings; plant corn having the same number of days to maturity at least ten days apart.
The All-Important Peak Maturity Period
The problem with growing standard sweet corn is that its peak maturity period lasts only two or three days. So if you want to eat corn that's truly sweet, you have only two or three days to pick, cook, and eat your harvest. As soon as you pick it, the sugars start converting to starches and the corn's taste degenerates. As Darbie M. Granberry points out in "You Can Grow the Sweetest Sweet Corn Ever", normal sweet corn loses one-half of its sugar when held at 80 degrees for 24 hours. You can see why I said you had to be vigilant! If you were on vacation when the peak period hit, you missed your chance to eat sweet corn that season.
The new varieties of sweet corn (SEs and Sh2s) convert their sugars to starches more slowly, giving us more leeway with corn harvesting and more time to use the corn we pick. How much time depends a great deal on the temperature. J.E. Ells, vegetable crop specialist with Colorado State University Cooperative Extension says that, "at 60 degrees, an ear will remain in prime condition for five days. At 85 degrees, it will remain in prime condition only one day." ("Sweet Corn for the Garden"). So when you pick corn that you're not going to use right away, you should refrigerate it. If you're not near a refrigerator, the National Gardening Association recommends keeping the freshly picked ears in single layers, (rather than stacking them) and covering them with a damp cloth ( "Harvesting Corn: Getting the Most from your Crop").
How To Tell if Your Corn is Ready
Corn is ready to be picked as soon as the ears have rounded out. Sounds simple, doesn't it? You can tell if the ear has rounded out by feeling it; the end should be rounded or blunt rather than pointy.
Many gardening guides tell you to check corn's maturity by using the thumbnail test, opening the corn husk and piercing a kernel with a thumbnail. If the corn is mature, the kernel will squirt "milk"; if it's immature, the liquid will be watery. You should try to avoid doing this if you can, however; as the National Gardening Association points out, if you open an immature ear, then it will be easy prey for insect and bird damage.
