Garlic needs about 9 months to develop fully. The secret to a harvest of large garlic bulbs is fall planting; generally four to six weeks before the soil freezes. This way the roots can become established before the winter sets in and will be ready to support vigorous leafy growth come early spring.
The cold of winter is needed to initiate the side buds that will ultimately grow and swell to become cloves (and in some types, to initiate the flower bud). The lengthening days of spring are the signal for the initiated but undeveloped side buds to start forming into cloves.
It is possible to sow in early spring and get a reasonably good harvest, but everything is against you - wet, difficult to work soil; no early root growth; less exposure to winter chill. Early Spring is possible, but definitely a second choice.
Garlic grows best on friable (crumbly) loamy soils that are fertile and high in organic matter. Gardeners who can grow onions can grow garlic since the culture is similar.
The soil must be kept evenly moist as dry soil will cause irregularly shaped bulbs. Heavy clay soils will also create misshaped bulbs and make harvesting difficult. Add organic matter, such as well-rotted manure or compost to the soil on a yearly basis to keep it friable.
How to Plant Garlic
Garlic is started by planting cloves that are divisions of the large bulb. Each bulb contains a dozen or more cloves; each clove is planted separately. The larger cloves yield larger mature bulbs at harvest. Do not divide the bulb until ready to plant‹early separation decreases yields. Select "seed bulbs" that are large, smooth, fresh, and free from disease.
Before planting garlic cloves, work in a couple tablespoons of general purpose granulated organic fertilizer into the soil several inches below where the base of the garlic will rest.
Plant garlic cloves three to five inches apart in an upright position in the row and set them at a depth of one-half to one inch deep. Setting the bulbs in an upright position ensures a straight neck. Be sure to allow 18 to 30 inches between the rows. Do not divide the bulbs into cloves until you are ready to plant since early separation results in decreased yields.
Mulching After Planting - Garlic roots and shoots can tolerate freezing conditions provided that sudden drops in temperature do not occur. Therefore, after planting, rows should be covered with a three-inch to four-inch layer of straw mulch, shredded leaves, pine needles, wood chips or a combination to moderate soil temperatures and minimize excessively fluctuating temperatures in the winter and early spring.