We just harvest the cabbage after the first frost. A couple frosts makes them sweeter, plus they "pre-chill".... if the root cellar is staying pretty cold by then, (under 50 degrees F) you're good. We remove as many outer leaves as necessary to get rid of slugs and earthworms, wh8ch like to hide in the first couple of layers. Then we wrap the well in several layers of newspaper, and lay them on shelves in the root cellar.
And yes, they are coming out crisp and sweet... we don't buy fresh vegetables out of season... cabbage and carrots are our main fresh veggies in winter, although I'll often grow some hydroponic spinach and leaf lettuce for a treat.
I've tried all the suggested methods of keeping carrots... damp sand, damp sawdust, maple leaves. The leaves seemed to work best of the "natural" methods. But the simplest and most foolproof, which can give us perfect carrots as late as May of the following year, is the perforated plastic bag method.
I staple a dozen or so gallon Ziploc freezer bags together, and then run them through my unthreaded sewing machine, with a fairly heavy (size 16, or a denim needle) needle. I sew around in freeform designs , enough so the bag has fairly even perforations all over the surface...I usually sort of crisscross them about 3"apart.
Put clean (not scrubbed... you don't want to damage the skins... just remove excess dirt) PERFECT carrots in the bags, immediately chill in the root cellar. As long as you don't accidently get carrots with wireworm damage mixed in, they will be sweet and crisp well into spring.
If you miss some damaged roots, they'll rot into mush, and make a mess of the whole bag. I generally only have that problem with the couple bushels I sort out for the horses.
We store potatoes, apples, carrots, cabbages, and occasionally beets (same way as carrots) in our root cellar. Contrary to all the expert advice, storing apples and potatoes close together doesn't seem to affect the potatoes at all. I often have to pull my Yukon Gold seed tubers out in May into a warmer place to get them to sprout in time for planting.
Onions are stored in mesh bags separately... we found that they'll keep into June (Copras... the best storage onion, EVER) if we hang them at the bottom of the stairs that leads to our basement... outside the door to the basement that stays cold. It holds at about 50-55 degrees, and the humidity is quite a bit lower Dothan in the basement proper.
Winter squash is stored on pallets in the basement, to keep them up off the concrete floor. They often keep a full year.
We also use the root cellar for storing olive oil and honey. We've had 10 year old olive oil in sealed jugs show no sign of rancidity, and the cool temperatures keeps the honey from crystalizing as fast as it does in warmer temps.
Summerthyme