Turnips are actually a member of the cabbage (or "brassica") family. In fact, there are a few varieties of Turnip, which have no root to speak of, are grown only for their leafy tops. But for the most part, they are root vegetables. Most of a Turnip is white or yellowish from having ground in the ground, but Turnip crowns are often purple or green from having poked above the soil to get a bit of sun.
Turnips flourish in poor soil where other vegetables struggle, and don't require a long growing season. They are resistant to frosts and mild freezing. And they used to be a veg that would keep forever (see storage below.) Turnips are more popular in the Southern United States than they are in the north. But they have a history of long unpopularity everywhere, as they were seen as a poor man's food, and even those who weren't poor cooked them wrong and made them taste bitter and Turnipy.
The most common variety is white and globe-shaped. But there are many different varieties, leading to confusion between what is a Turnip and what is a Rutabaga and what is a Swede. Thankfully, you can use them all interchangeably. See separate entries on Swede and Rutabaga to understand the actual differences.
Younger and smaller Turnips -- less than 3 inches (7.5 cm) wide -- will be sweeter and more tender. Don't buy any that are soft or shrivelled; they should feel "hefty" for their size. Larger Turnips may be tougher and a bit bitter. Sometimes the Turnips will come with the greens attached still; sometimes they will come with the greens already removed. It depends on when in the year you are buying them. If the greens are fresh, crisp, bright and green; you can cook with them. Otherwise, they won't be bad, they'll just be unappealing. Young greens can be eaten raw in salad, older ones need to be boiled, steamed or microwaved with a bit of water -- as you would spinach. The raw greens will add a perky, mustardy taste to your salad greens.
Younger Turnips can be sliced up and served raw, for instance as part of a fresh veg and dip platter, or shredded for use in a coleslaw, etc. Older, big Turnips won't have as mild a flavour so you won't want to use them raw. But overcooking any Turnip, whether young or old, makes them taste "Turnipy" -- as in the overboiled Turnip taste we all grew to hate. Another way to avoid that Turnipy taste is to leave the cover off the pot a bit when boiling, which allows gases to escape that would otherwise get trapped in the water and make the taste stronger (same principle as for cabbage, which Turnip is related to.)
Turnips are best cooked in enamel or stainless steel pots as the Turnip may interact with aluminium or iron pots and go dark. Turnip is quite uninteresting on its own, but is very good combined with other vegetables such as parsnip, carrot and potato, either mashed with cream and cheese (got any pieces of bacon to toss in?), or diced with butter.
If Turnips are less than 3 inches (7.5 cm) wide, place in pot of boiling water for about 20 to 30 minutes or until tender. If Turnips are larger, halve them. If you are in a hurry, you can dice or slice your Turnips, and reduce cooking time to 6 to 8 minutes.
Cube or slice the Turnip, place in a covered microwave-proof dish along with a few tbsp of water, and zap for anywhere up to 9 minutes, depending on the zap power of your microwave. Let stand covered for 3 minutes after removing from microwave. Prepared this way, they will be particularly uninteresting.
Prepare as for boiling, then steam. Will take about the same time as boiling for whole Turnips, cut up Turnips will need to be steamed for up to 15 minutes.
Quarter the Turnips, and about 45 minutes before your meat will be done, place in roasting pan alongside the meat.
Some Asian recipes will have you stir-fry Turnip. The Turnip is cut into thin slices or shredded, then stir-fried with other ingredients. Small cubes also works.
1 pound (450g) of chopped raw Turnip equals about 4 cups of chopped or about six 3-inch (7.5 cm) Turnips unpeeled, without tops
Commercial storage of Turnips requires a humidity of 90 to 95%, which can be achieved -- commercially. But we can't at home, outside of root cellars. And a quick reality check, in case you had a nostalgia moment there about root cellars: spiders, bugs, rats....
So, modern storage guidelines are: if the Turnips came with tops (the leaves still on), and you plan on using the tops, cut off the leaves, bag them separately and refrigerate for use within a few days at the most. Refrigerate the roots unwashed in a plastic bag. They should keep for anywhere from 1 week to 2 weeks, depending on your refrigerator.
To freeze, wash, peel, slice and place in pot of water that just covers them. Bring the water just to the boiling point, then drain water off the Turnips (why not drain into a bowl and freeze to use as part of a tasty stock one day?), dump the Turnips into a sink of very cold water, then drain again, pack in freezer bags and freeze.
Turnip continued to be a staple food in the Middle Ages. The variety that we use today emerged then. They were dead easy to grow and keep, and provided starch and filler to many dishes. And, until pumpkins came over from America, that's what Jack O' Lanterns were made from.
But then, along came the potato when explorers returned from the New World. Not that the potato caught on right away, but as people became exposed to it and were able to grow potatoes, who wouldn't be fed up after eating just Turnip for 1,500 years? Plus, potatoes are more nutritious. Not that anyone would have hefted a potato in one hand and said, "potassium and vitamin C content feels better to me", but they would have noticed the effects in their diet.
While potatoes were coming to Europe, the Turnip was passing them mid-Atlantic and reaching the Americas. Jacques Cartier's men planted them in Quebec in 1541, and Virginia colonists planted them in 1609.
By the 1700s, potatoes were definitely elbowing their way into the local Turnip patches.
Turnips got a boost in 1730. On farms, many livestock were slaughtered in the fall simply because it was too difficult to try to afford to feed them economically over the winter. Viscount Charles "Turnip" Townshend (1674-1738), a Brit, began experimenting and found that cattle thrived on Turnips, which were cheaper than growing and storing hay all winter. In fact, Turnips had been fed to livestock before this, but his experiments documented that Turnips were good for cattle and highlighted to farmers the economies to be realized. So, Turnip cultivation got a whole second life, and Turnips turned from being primarily a human food to being a livestock food. In the Victorian era, Mangelwurzel would come to rival Turnip as a food stock for overwintering livestock.
Literature & Lore
Note, however, that what the Scots today call "neeps" is not Turnip, but swede.
"I didn't just fall off of the turnip truck" is a colloquial phrase meaning "I'm not that dumb". The allusion is, perhaps, to some country rube arriving in the city with a load of turnips, which is itself a lowly country vegetable. Incidentally, rube, or more precisely "Rübe" is a German word for Turnip.