Let’s call them earth vegetables, because the name “root vegetable” doesn’t always quite fit. A potato, technically, is a tuber — that is, an enlarged underground stem. A kohlrabi, on the other hand, is an enlarged stem that sits just above the ground. Beets, carrots, parsnips, turnips and rutabagas are all true roots, of a type called a taproot. And a celery root is actually a swollen hypocotyl, which grows in the space just below the seed leaves and just above the root. But never mind. What’s important about this motley clan of food storage organs is that they make great winter food.
All of them grow either in or in very close contact with the soil, and are comfortable there. So when fall comes and you’re wondering when to harvest them, think about how long you can keep them exactly where they are. The approach of winter brings out the best in them, and their flavor will only improve while they’re sitting in the garden. Some can stay longer than others. Kohlrabi, celery root, beets, turnips and rutabagas can all take some frost, but should not be allowed to freeze hard or they won’t keep as well. So into the root cellar they go, or — try this! — into a garbage can or large picnic cooler, sunk into the ground with an insulated lid. Perhaps you have a cold, unfrozen shed, a spare fridge, or a cold, walled-off section of the house cellar. Any of those would work, as long as you splash water around from time to time to keep the air moist. Remember, you’re trying to create a place that is cold, dark and damp, just like the ground, because that’s where earth vegetables want to be.