Since the "planting" garlic sometimes found in garden centres in the spring is often somewhat expensive and isn't always available as early as you might want to plant, I decided last spring just to plant a couple of bulbs I bought from the grocery store.
This experiment seemed to work well. I separated the cloves and planted them early in the spring. They quickly sprouted and were not affected by cool weather. Eventually, the tops died down and I pulled them out of the ground, where I was actually surprised to see that they appeared to have formed bulbs!
I braided the tops together and hung all the cloves in a dark storage room in our basement, where they appear to be keeping very well. I have used several bulbs for cooking, and the flavour is very good.
Unfortunately, several of the bulbs that I have used didn't actually form cloves the way they should have. From the outside, they appear normal, but when they are opened, there are one or two regular cloves on the outside, and one giant clove in the middle. Although they seem to be storing well and the flavour is good, the big part of these garlic bulbs is awkward to cook with, because it is usually bigger than the two or three cloves that most recipes call for. I'm also not sure how well it would grow if I replanted it.
Why didn't my garlic form cloves? I did everything you are supposed to when planting garlic in the spring: I selected a softneck variety, planted early, and gave it plenty of time to mature. However, many varieties of garlic are, like onions, sensitive to daylength, and the variety I ended up with may not have been appropriate for short spring days and long summer days, since it was probably originally grown in California.
So the solution for the next time I grow garlic is probably to either find a variety more suited to my area, or grow hardneck garlic, a hardier type that is usually planted in the fall and allowed to overwinter. Hardneck garlic is often available from mail-order catalogues, but it is sometimes only available in large quantities with extra shipping fees tacked on, so a local source would be better, if I can find one.