The period is between pollination in early July and the time that tasseling occurs a month later.

Tasseling is when the strings for pollination grow at the top of the stalk.

It's setting moral atmosphere, boosting character development, orchestrating everything from action to elegy: "Charlie died in May, and the long, buttery Chesapeake summer moved through plantings, through the flowering of the soybean plants toward the tasseling of the corn."