For a complete discourse on the management of winter greens you are invited to inspect Vegetable Gardening the Colonial Williamsburg Way, 18th Century Methods for Today’s Organic Gardeners (Rodale Press).
In the frosty days of mid-winter, plant growth comes to a halt but the prudent gardener has stocked the garden with plants that will withstand the cold and may be harvested at leisure. Cabbages, once they have formed their heads, are extremely tolerant of freezing and become even sweeter as the weather becomes colder. It has long been believed that it is a great help to earth your cabbage before the ground freezes. This will hold their heads erect and prevent the frost from penetrating the ground to their roots. Before the plants are earthed it is advisable to cut away the bottom leaves, this will not only facilitate the task but will remove the lower leaves which are apt to yellow and rot. As John Evelyn reminds us, “Remember to cut away all rotten and putrify’d leaves from your cabbages, which else will infect both earth and air.” There are few smells as objectionable as that which comes from rotting cabbage leaves, and the gardener will find that a tidy garden is a more pleasingly fragrant garden. At the approach of severe weather the gardener need only provide a brush mulch to preserve the cabbages. We keep a couple of privet bushes along the fence line to the orchard for this very purpose. When the brush is wanted we cut them as you would a pollard and then simply lay the boughs over the plants. With this small precaution you will be able to harvest cabbage at your convenience throughout the winter. I have often pulled cabbages that are frozen near solid and yet their hearts remain crisp and sweet. For those that live in colder climes you may heed the words of Mr. Hanbury who advises that the gardener dig a trench in which to transplant their cabbages. Then you may set, “the Cabbages close to each other against the sides of the ridges, burying the stalks in the ground, and this in some measure secures them against the inclemencies.” A covering of straw or brush will greatly improve their chances of surviving the severest weather.