Overwintering vegetables: Tree Collards
Tree collards: Brassicaolercea oleracea
With a flavor like kale, and a host of nutrients, Collard greens are a staple food in the American South, where they are typically cooked with ham or bacon. But tree collards have been an elusive prey of mine: their secret was heavily guarded within the minority community and only recently available to the general public.
Their history and biological identity seem to be shrouded in mystery, but Tree Collards are reputed to have come from Africa and have been preserved and passed on within African-American communities in America. They do not normally flower or make seed; if they do the seed does not breed true. So propagation is by cuttings, which are passed along from gardener to gardener.
Growing tree collards are much like growing regular collard greens or kale except that they are 5-6 feet tall (hence the name) with purple-tinted leaves that grow up a tall, single stalk. They are a lovely addition to any food forest or perennial garden and can also be eaten fresh, like kale, in salads. They are definitely perennial where I live in Zone 8 and through Zone 10, and maybe will overwinter in sheltered areas in USDA Zone 7, depending on the conditions. In colder zones, if you have established plants, you can try taking cuttings as winter begins and rooting them indoors for planting outside the following spring. You should make 12" cuttings. Half the nodes on it should be below the soil to form roots, and the other half of the nodes should be above the potting soil, to form leaves. Make several cuttings in case some of them fail!
Tree collard greens are especially tender and delicious in cool weather, so they are a good choice for a low-maintenance winter vegetable in mild climates. (They're pretty good in warm weather, too.) And the nutrition! Collard leaves are rich in calcium (226 mg per cup, cooked), vitamins B1, B2, B9, and C (which may be leached by cooking, so eat some raw for that, as well as beta-carotene. They are high in soluble fiber and like most cruciferous vegetables contain multiple nutrients with potent anti-cancer properties.
Here is a supplier: http://www.bountifulgardens.org/Tree-Collards/products/141/