Usually started from their cloves rather than seeds, garlic plants (Allium sativum) include the varieties soft-necked (Allium sativum subsp. sativum), hard-necked (Allium sativum subsp. ophioscorodon) and elephant or great-headed (Allium ampeloprasum). Most garlic plants grow only 1 to 2 feet tall, but elephant types can reach 5 feet in height. Garlics vary in hardiness from U.S. Department of Agriculture plant hardiness zones 2 through 10 and should be planted just after the first autumn frost, allowing them four to six weeks to grow before a deeper freeze. In USDA zone 5, therefore, the best time to set garlic cloves in the ground is between mid-October and mid-November.
Purchase garlic heads that are intended for planting because garlic in grocery produce sections may have been treated to prevent them from sprouting. For the best results in USDA zone 5, choose hard-necked types of garlic.
Although some soft-necked and elephant varieties also are considered hardy in USDA zone 5, it is the northernmost extent of their range. So they may not perform as well there as the more cold-resistant hard-necked types do. Soft-necked varieties store the best, however, and elephant types grow the largest, and so you may want to try a few of them anyway.
Wait until just before you intend to plant the garlic to separate its heads into cloves, leaving the paperlike husks on those cloves. Rodale's Organic Life recommends pretreating the cloves to help stave off fungus diseases. Do so by soaking the cloves for 2 hours in 1 quart of water to which you added 1 tablespoon of baking soda and 1 tablespoon of a liquid seaweed emulsion such as 0-0-1.
After draining the cloves, plant them while they are still damp. Choose a site in your garden with rich, well-drained soil – preferably with a pH between 6.2 and 7 – in full sun. If the soil is poor or poorly drained, then blend a 1- to 2-inch-thick layer of compost into the top 1 foot of the soil to improve its fertility and drainage. Avoid planting garlic where other Allium species have grown within the previous three years.
Use a hoe to make a furrow about 2 inches deep the full length of your planting row, and position the cloves in the bottom of the furrow with their flat bases down and pointy tips up. Space soft-necked or hard-necked garlic cloves 4 to 6 inches apart -- in rows about 12 to 15 inches apart, and fill the furrows with soil to cover the cloves. Double the depth and spacing for the elephant types. Water the soil well, and place a 3- to 5-inch-thick layer of straw or chopped dead leaves on the soil surface to act as mulch.
If autumn is particularly dry, then the garlic may need water occasionally while the cloves establish roots before the ground freezes. After the soil freezes, the plants should remain dormant all winter. When they begin to grow in spring, ensure their soil receives about 1 inch of water per week from rain, irrigation or both, but never allow the soil to become soggy.
In early spring, remove some of the mulch, leaving about a 2-inch-thick layer of it in place to help protect the young garlic sprouts and suppress weeds. After the garlic plants have begun to grow, feed them once every two weeks by spraying them with a solution of 2 tablespoons of 0-0-1 seaweed emulsion mixed into 1 gallon of water.
Remove all flower stalks that attempt to form on the plants in early summer; doing so concentrates all of the plants’ energy into their bulbs. The bulbs should be ready for harvest in midsummer, when about two-thirds of the plants' foliage has died. Don't water the plants during the two-week time period before you plan to harvest their bulbs.