Hardy in U.S. Department of Agriculture plant hardiness zones 4 through 9, garlic is a biennial grown as an annual, usually planted in fall and harvested the next summer. A biennial grows during one year and flowers in the second. Garlic can act like a perennial plant if bulbs aren't harvested, with new plants growing from the cloves.
Getting Planting Stock
Growing garlic gives you a major advantage over buying it: You can choose different varieties of garlic with rich and unique tastes and known growing traits. Supermarket garlic is often treated with a growth inhibitor to retard sprouting, and bulbs can be from varieties not well suited for the climate. Nurseries sell garlic starts as do many seed companies. Once you acquire a variety with a taste you like and that grows well, reserve some of the crop for replanting the next season.
Timing Garlic Planting
Although you can plant garlic in the spring, fall-planted garlic has a longer time to establish and produces larger garlic bulbs at harvest. In temperate areas, time the planting for after the first frost and about four to six weeks before the ground freezes. In the spring, plant garlic after the ground thaws. In mild winter climates, planting time goes from late October to November or December. The goal is to get bulblets in the ground in time to form a good root system before cold weather sets in.
Preparation for Planting
Keep the head of garlic intact until just before you plant it. Then separate the individual cloves, leaving the papery layers of skin around the bulblets undisturbed. Choose the largest cloves for planting and save the smallest for kitchen use. Plant the cloves immediately upon separating them.
Soil and Spacing
Garlic needs loose, fertile, well-draining soil and a sunny location. Before planting, work the soil loose to a depth of 12 inches. Add 1 to 2 inches of organic material such as aged compost or aged manure and dig it in. With the pointed end up, plant garlic cloves 4 to 6 inches apart. In cold winter areas, cloves should be 2 to 4 inches under the soil. In warm winter climates, put cloves 1 to 2 inches deep. Rows should be 1 foot apart. To insulate bulblets from cold temperatures and prevent weeds, mulch the planted area with 3 to 6 inches of organic mulch such as straw or grass clippings.
Watering and Fertilizer
After planting the cloves, keep the soil moist but not soggy to encourage root formation. In cold weather, reduce watering since wet conditions can cause bulbs to rot. When you see new green shoots emerging to signal new growth as weather warms, resume regular watering so bulbs form well. A good guideline is to water when the top 1 inch of soil is dry. Fertilize in early spring when there's strong new growth and again a month later. Applyliquid fish emulsion at the rate of 6 tablespoons for every 1 gallon of water, spraying the foliage and soaking the soil around the plants.
Depending on the variety, planting time and climate, harvest garlic from early to midsummer. Mature plants have five or six leaves. Cut back on water as leaves begin to show yellow. When about half the leaves are yellow, carefully lift up bulbs with a garden fork, taking care not to damage them. Pull out the lifted plants, shake off extra dirt and lay them out to dry in a shady, airy place protected from rain.
Bulbs are ready for cooking right after being dug up. For storage, allow plants to dry for several weeks, trim stalks to 2 inches above the bulb and cut dry roots back to near the bulb. Brush off any remaining soil and store the bulbs in mesh bags in a dark area with good air circulation. For softneck garlic, braid the dry stems together. Effective storage temperatures are 50 to 70 degrees Fahrenheit. Hardneck garlic keeps for six to 10 months, and softneck varieties last up to 12 months.