Winter greens

A recent comment had me thinking about winter greens and their response to the lengthening and warmer days to come in spring. Hardy kales, cabbages, and collards are able to withstand the frosts and freezes of winter because of their leaf chemistry and built-in ability to produce natural 'antifreeze.' But they don't have the ability (nor does much else) to grow very vigorously at low temperatures. So our winter vegetable gardens are basically in suspension, until warmer temperatures support the physiological functions that convert sunlight to sugars and drive cell division and expansion.

So collards or hardy lettuces in an unheated greenhouse can be harvested all winter, but won't start new growth until it's warm enough again.