Garlic (Allium sativum)
Jeanine M. Davis
Extension Horticulture Specialist
Garlic is a popular pungent herb which has been used for culinary and medicinal purposes for over 5,000 years. It is a close relative to the onion and belongs in the Amaryllidaceae family. Although it is a perennial, it is usually grown as a winter annual in the South. The plant consists of four or more flat, grayish green leaves which are about 12 inches long and a half inch wide. The edible bulbs are composed of thick modified storage leaves called cloves. The papery, outer covering on the bulbs varies in color from red to white. Some strains of garlic produce a 2 to 3 foot flowering stalk which may produce a cluster of small cloves called bulbils. Most cultivated garlic plants do not produce true seed. Thus, almost all garlic is propagated vegetatively from cloves and bulbils.
There are two main types of garlic; softneck (also referred to as silverskin, common, artichoke, or Italian) and hardneck. Softneck garlic is the kind usually available in the supermarket. It grows in most areas, rarely produces a flower stock, stores well, and has good flavor, but the cloves are difficult to peel. There is a wide variety of interesting hardneck garlics, but they tend to be more finicky about where they will grow. They also tend to produce a flower stock, do not store well, may or may not have good flavor, but they do peel easy! Without prior experience, it is difficult to know if a commercial variety of garlic will do well in your area or not. If you have never grown garlic before, consider buying small quantities of several varieties and testing them for a year or two. Another strategy is to secure garlic from a successful local garlic grower or gardener. Avoid planting the Creole types of softneck garlic (also called Early, Louisiana, and White Mexican) in western North Carolina because they are not very winter-hardy and do not store well. Recommended varieties for commercial production in North Carolina include German Extra Hardy (hardneck), many of the Italian varieties (softneck), and New York White Neck (softneck). Elephant garlic (Allium ampeloprasum) is a leek, not a garlic. It produces a bulb up to four times larger than garlic and is much milder in flavor. It can be produced like garlic and grows well throughout North Carolina.
In North Carolina, garlic should be fall planted from mid-September (western NC) through November (eastern NC). The cloves must be planted early enough for large root systems to develop before winter begins. A well-established plant will grow rapidly in the early spring as temperatures begin to rise. Spring planting of garlic is not recommended because the bulbs from spring planted garlic are usually very small and must often be allowed to grow a second season to reach marketable size.
Most strains of garlic require a cold period for about 2 months at 32° to 50°F to initiate bulbing. Fall planted garlic achieves this naturally, but spring planted garlic may benefit from a few weeks in cold storage (at less than 40° F) to produce larger bulbs. The bulbing response is stimulated by long days and warm temperatures in late spring. It is during this time that a flower stalk will develop on some varieties, particularly those of the hardneck types. To achieve the largest bulbs, break off the flower stalk or pinch off the flower buds. The young, unopened flower buds are edible and often used in spring salads. If the flower stalk is allowed to grow, the aerial bulbils that develop on some varieties can be used as planting stock that will produce marketable size bulbs in two to three years.
Store planting stock as whole bulbs, breaking the bulbs apart into individual cloves just prior to planting. Plant only damage and disease free cloves. If large bulbs are desired, plant only the largest cloves.
Plant cloves points up, 1 to 2 inches deep and 2 to 6 inches apart in the row. A common planting arrangement is 4 inches by 4 inches in triple rows on beds. Cloves that are fall planted too shallow are prone to winter injury. Although garlic is quite hardy, fall planted garlic can be mulched with straw or some other organic material for extra winter protection.
Plant garlic in a fertile soil high in organic matter with a pH of 6.2 to 6.8. Fertilize according to soil test recommendations for garlic. In moderately fertile soils, apply about 75 pounds nitrogen, 150 pounds phosphate, and 150 pounds potash per acre and disk about 6 inches deep before planting. When plants are about 6 inches tall (usually mid March), top dress with 25 pounds nitrogen per acre and repeat in early May. Apply all top dressings to dry plants midday to reduce the chance of fertilizer burn.
Good soil moisture is required during the growing season to produce large, well-shaped bulbs. This is usually provided by overhead irrigation. As harvest nears, however, irrigation should be halted to prevent deterioration of the bulbs.
Insect and disease problems are similar to onions. To prevent many of the problems that can arise, follow a strict crop rotation plan for garlic. A minimum of four years should pass between Allium plantings in a field. Follow good sanitation practices by purchasing clean planting stock, not planting any cloves that look diseased or deformed, and removing diseased looking plants from the field. If soils are too wet, root rot fungi and bacteria may be a problem. During hot, dry weather, thrips populations may reach damaging levels. If thrips counts exceed an average of 5 thrips per plant, control measures should be taken. Garlic is a weak competitor against weeds. Organic mulches can be applied to reduce weed growth. Careful, shallow cultivation is also recommended. Recent research in other parts of the country indicate that flame weeding may be the most cost-effective method for maintaining clean beds in garlic fields.
Garlic may be harvested when the leaf tops begin to discolor and dry. If the bulbs are immature when harvested they will tend to shrivel when cured. If harvested too late, the bulbs may be discolored and the outer papery covering will break down exposing the individual cloves. When a few of the tops begin to fall over, pull a sample. Garlic is ready for harvest when the cloves are fully segmented but the bulb is still tightly encased by an intact outer skin. Elephant garlic is ready to harvest in mid-May to mid-June and must be harvested when about 30% of the foliage is starting to yellow. If harvest is delayed past that point, the bulbs begin to split open, revealing the individual cloves.
When the optimum harvest time is determined, run a cutter bar under the bulbs to cut the root system and partially lift the bulbs. For small plantings, the soil can be loosened with a fork and the bulbs pulled by hand. The bulbs are often pulled, gathered into windrows, and allowed to dry in the field for a week or more. This is only appropriate during dry conditions. Otherwise, the garlic should be gathered and cured under cover.
Garlic yields vary greatly depending on location, spacing, and variety used. In general, yields range from about 3 tons to 8 tons per acre in this region with about 6 tons being the average.
Garlic must be cured for several weeks prior to storage. In areas where morning dew or rain is not an issue, field cure the bulbs by leaving them in windrows. Otherwise, place the bulbs in slotted vegetable bins in a covered but open area to cure. Small volumes of bulbs can be hung in the rafters of barns, garages, and packing houses. Under very humid conditions, the bulbs can also be cured on racks in forced air dryers. The bulbs must be thoroughly dried before being shipped or stored. After curing, discard diseased and damaged bulbs. Clean the remaining bulbs to remove the outer loose portions of the sheath and trim off the tops and roots.
When properly cured, garlic keeps well under a wide range of temperatures. Store in open-mesh sacks in a dry, well ventilated storage room. Optimum storage conditions are 32° to 35° F with 60% to 70% relative humidity. Storage life is 5 to 8 months.
Most garlic in North Carolina is sold directly to the consumer at roadside stands, tailgate markets, farmers’ markets, and through classified ads. This method brings the highest returns to the farmer. Wholesale garlic prices in 2006 often ranged between 0.85 to $1.20 per pound. At the same time, elephant garlic was selling wholesale for $2.60 to $3.65 per pound. Garlic braids, only available summer through Christmas, sell for $20.00 or more a piece retail and about $2.50 per pound wholesale.