“The plants mature according to the approximate amount of heat they receive, starting from planting. “It all goes by growing degree units, GDUs,” Dave told me. One GDU is added for every degree the average daily temperature exceeds 50°F. So, for example, a day with an average temperature of 65° would be counted as 15 GDUs. “And they know how many GDUs it takes for the female hybrid to get to pollination and how many GDUs it takes for the male to get to pollination, so that nick happens at the same time,” Dave said. “If you put them all in at once, your male could shed pollen before the female has started to silk, and you get no pollination. If that happens—and it has—you can lose a whole crop.” “That’s why weather is such a big deal,” Dave continued.”
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Ted Genoways,
This Blessed Earth: A Year in the Life of an American Family Farm