When to plant - You'll have to research this for your own part of the country, and perhaps you'll determine the timing better than my research yielded. I've seen instructions to plant in my area (zone 7) ranging from early fall to the winter solstice, Dec. 21. My experience has been that I harvest full heads in June when I plant in September, and I've read that garlic needs 9 months to mature. If you plant by the lunar calendar, root crops are planted during the two weeks after the full moon.
What to plant - Each planted garlic clove will grow into a full head, and you need to start with a head of garlic. Don't just buy a head at the supermarket and expect good results… produce department garlic is often treated not to sprout! Great if it will sit on your kitchen counter while you use it, but not good if you bury it in the ground and expect it to grow. You can buy garlic to plant from seed catalogs (like Seeds of Change, Hood RIver Garlic), you can buy from sources which you know don't treat it - like a local farmer - or you can save some of your own harvest to replant the next season. I bought mine from the nearby Mennonite Community farm stand. The yield sign I photographed on the road to the farm is pictured above - you don't see many of those graphics around these days!
Choose a Variety - To simplify, there are three types of garlic you can plant: hard neck (a very stiff straight stem in the center of the cloves), soft neck (no center stem), and elephant. The elephant is more closely related to leeks than to garlics, and some say it has only a mild garlic flavor, but I find it plenty strong. I love how easy it is to peel and get lots of garlic all at once! Hard neck varieties - like the Spanish Roja, a "Rocambole" type I bought from the Mennonites - are known for superior taste and easy peeling, but they don't store for long periods. Soft neck garlic heads tend to grow larger than hard necks, have superior shelf life, and are particularly good for warmer climates, but might be lacking in flavor. I've planted all three types in my garden.
Where to plant - I plant my garlic right in the vegetable garden, in an area that won't be rototilled in early spring, since I won't harvest until early summer. I have successfully dug up young sprouting garlic at the end of winter, tilled the area, then replanted, but I'm sure they do better without such disturbance. Plant in prepared fertile garden soil, good sunlight, good drainage, and a pH of 6 to 7.
How to plant - Don't break the head of garlic apart until you are ready to plant, or the cloves might dry out too much. In all cases, the larger the clove, the bigger head it will grow… plant the largest cloves from your "seed" head, eat the small ones, and discard any which look unhealthy. When ready, plant each clove 5 to 6 inches apart, with root end down and tip end up. I have had the best results planting each clove 3-4" deep, and up to 5-6" for the elephant garlic cloves. You can mulch with decomposed leaves or straw on the bed during the winter, especially in colder climates, but rake off the mulch in the spring to avoid mold, slugs or snails, and to give the plants some sunshine. If frost turns the green tops yellow, it will not harm the growth of the garlic bulb.
Plant your garlic this fall, and I'll update you on growing and harvest garlic early next spring. And you'll see lots of the recipes I post will call for fresh garlic. For me, I can't grow too much garlic!