Softnecks and Hardnecks
Your first choice is between hardneck garlic (Allium sativum var. ophioscorodon) and softneck garlic (A. sativum var. sativum). Or perhaps a few of each—garlic takes up little room and cross-pollination is not an issue, so there's no reason not to grow as many varieties as you can lay your hands on. Here are the key differences between the two subspecies:
Softnecks are adapted to a wider range of climates, they keep longer in storage (which is why supermarket garlics are almost always of this type), they tend to mature faster, and they're generally more productive than hardnecks. The stems of softnecks are easier to braid, but the cloves are comparatively hard to peel.
Hardnecks demand a little more attention than softnecks to produce good-quality large bulbs. But they are more colorful and offer more variety of flavor. They also produce a flower stalk or scape, prized for its delicate flavor when harvested in spring while it is still tender. Removing the scape also encourages more vigorous bulb production. (Some softnecks can occasionally develop flower stalks.)
North and South
Within the broad categories of hardneck and softneck, garlic is further classified into five types: The Purple Stripe, Porcelain, and Rocambole types are hardnecks; Artichoke and Silverskin types are softnecks. Which are best for your climate?
Most of the hardnecks do best where winters are cold, spring is damp and cool, and summer is dry and warm—that is, in the Northeast, Midwest, northern tier states, and Canada—advises Bob Anderson, owner of Gourmet Garlic Gardens in Bangs, Texas. Rocamboles and Purple Stripes, in particular, thrive in more frigid winters and cool springs, he says. Porcelains can fare well in warm-winter climates in years when winter and spring tend toward the cooler side.
In the South, on the West Coast, and wherever winters are moderate, softnecks are the least fussy, Anderson says. In particular, he recommends 'Creole Red', an exquisite burgundy Silverskin with a unique clove pattern and "a taste that is full but almost devoid of heat." Other Silverskins, Artichokes (the standard variety in most supermarkets), and some of the marbled Purple Stripes (particularly 'Metechi') also do well where winters are mild, he says.
When choosing any varieties for your climate, consider their place of origin. 'Siberian', 'Bogatyr', and 'Choparsky' (all hardnecks with large cloves) come from cold and icy Russia, so it follows that they'll perform well in northern zones of North America. 'Polish White' (a softneck also sold as 'New York White') is adapted to the cold winters of Poland and so will also do well in cooler areas of the United States. If you garden in a more moderate climate (humid or dry), try 'Creole Red' (from Louisiana and California), 'Guatemalan Ikeda', 'Chelote' (from an island near Chile), or 'Xi'an' (from China).
Despite all of these preferences, garlic is highly adaptable over time, particularly when pampered. In my moderate northern California climate, I successfully grow several varieties of each of the five main types, including 21 Rocamboles. If you find a variety that really moves you, give it at least two or three years to adapt to your conditions and see what happens.
Farmers' markets and the many garlic festivals held throughout North America each year present excellent opportunities to find varieties suited to your conditions and your individual taste (a personal point indeed because we all have different body chemistries). You can ask the local growers which varieties perform best for them and probably buy some from them, too.