Notice when the silk strands appear.
image by Andrew Beierle/sxc.hu
There are a plethora of corn varieties that are either white, yellow or bicolor. Fortunately, you can grow corn in such a way that you can harvest corn for a couple of months. Simply plant several varieties, each with their own mature time. In addition, stagger the plantings of the same kind so they are ready for harvest at different times. Expect each stalk to produce only one or two ears of corn.
Know when the corn was planted and estimate when the corn is about ready to be picked based on its variety. For example white "Aspen" corn is ready to harvest in about 83 days while white "Kiss n' Tell" corn is ready to harvest in about 68 days.
Notice when the silky stands first appear out of the ears. It takes about 20 days for the ears to mature from this point.
Gently squeeze the corn and check one to be sure. The kernels should be plump and smooth. Poke a hole with your fingernail in one of the kernels; it should excrete a milky juice.
Harvest--or pick--the corn. After using all the above measures do determine when your corn is ready to be harvested, grab the ears at the bottom and quickly push it down. Twist and pull it off. It should snap right off.
Eat or refrigerate the freshly harvest corn as soon as possible. Either cut your cornstalks down or pull them out after harvesting.