WEST GARDINER — Early this month, a moment of reckoning came for vegetable growers around Maine. The maritime tropical air that had been over the state, sending daytime temperature into the 50s, was replaced by cold blasts from Canada and the Arctic. By Nov. 10, the temperature had plummeted into the teens and 20s. “It was like doomsday,” said Kevin Leavitt, a farmer who grows 20 acres of greens, beans, corn and other vegetables in and around West Gardiner. He worried the cold snap would kill many crops still planted outside, so he harvested as many of them as possible – carrots, potatoes, squash – and stored them in a freezer or a walk-in cooler.