A pril at the Greenmarket is known as that bleak interregnum between last year’s apples and potatoes and the first tender ramp. But this year had two unexpected, almost subversively early bright spots: corn and tomatoes, both sweet, juicy, and, yes, locally grown. Was global warming to blame, or some brazen flouting of Greenmarket rules? Nope. Just some savvy infiltration of a couple places that know no season: greenhouses and the freezer case. Last summer, when Ken Migliorelli’s corn was in, he cooked up a bunch, stripped the kernels, and froze a thousand small bags ($4 each). “I’ve been eating it all winter,” he says. “Tastes like it was just picked.” We’d concur, and so would Colin Alevras, who’s been using the corn for a creamy sauce he serves with mackerel at the Tasting Room. More recently, Shushan Valley Hydrofarm made its Union Square debut with a stand full of plump, red tomatoes and fragrant basil plants, both traffic-stopping anomalies among the cellared roots. Eleven years ago, owners Wayne and Phyllis Underwood sold their dairy herd and built a quarter-acre greenhouse on their Washington County farm, but only this spring started making the eight-hour commute to sell their delicious hydroponically grown beefsteak and vine-cluster hybrids to tomato-starved Manhattanites ($3.99 a pound, Wednesday and Friday). Not everyone is willing to pay for superior flavor and the locally grown factor, though. “People complain about the price,” says Migliorelli, “but we’re not set up like Birds Eye. This year we’re gonna get a machine that takes the kernels off. Last year, we did it with a knife.”