Garlic

Introduction

Garlic (Allium sativum L.) is in the onion family. For thousands of years, it has been grown for culinary and medicinal uses.  Garlic grows in a wide range of conditions. While most production is in mild areas, such as California, some varieties grow well in cold climates, often with better flavor. 

Types and Varieties

There are two main types of garlic. Hardneck (or topset) garlic produces false flower stalks called scapes, which are also edible. It typically has about a half dozen cloves per bulb. Softneck garlic typically has more than twice as many cloves and generally has a longer storage life than hardneck varieties.  Softneck garlic dominates commodity production, but many growers in New England prefer hardneck types for retail sales due to their flavor and appearance.  Hardneck varieties often have a reddish-purple clove covering versus the white color common in softneck types. Elephant, or great headed garlic (A. ampeloprasum) is grown like other garlic but has a milder flavor and is not widely grown in New England.

After centuries of cultivation, garlic has lost the ability to produce seeds. Therefore, it is vegetatively propagated by saving bulbs and planting individual cloves from which new bulbs form. The small bulbils produced on hardneck scapes can be used for propagation, but it takes several years of planting and selection to achieve marketable size bulbs.

Although many different variety names are used in garlic commerce, recent genetic research suggests there are only about 10 major varieties of garlic. These express different characteristics from one location to another, complicating variety identification. Since there is no standardization of varieties, as with potatoes, one must take garlic variety names with a grain of salt. As with other vegetatively propagated crop plants, diseases and mites can be carried over from one generation to the next. It's a good idea to start out with several different varieties and/or seed-sources produced by reputable producers in your area, selecting and saving seed from varieties and individual plants that perform best and appear to be free of pests.

Soil Fertility

A well-drained soil with good tilth and plenty of organic matter is ideal for garlic.  Garlic has a shallow root system; excess moisture, compaction, or droughty conditions will reduce yields. The optimum soil pH is between 6 and 6.8. Since garlic commences growth very early in the season, it is important to have soil nutrients available at that time. The table below gives timing guidelines for use of quick-release sources, particularly for nitrogen. Adjust timing if using a slower release material. Since garlic has such an early start, avoid fields that are slow to drain in the spring. Sidedressing with 20-40 pounds of N every 3 weeks until 4-6 weeks before harvest will produce optimal yields.

PLANT NUTRIENT RECOMMENDATION ACCORDING TO SOIL TEST RESULTS FOR GARLIC
GARLIC NITROGEN (N) LBS PER ACRE PHOSPHORUS (P) LBS P2O5 PER ACRE POTASSIUM (K) LBS K2O PER ACRE
SOIL TEST RESULTS   VERY LOW LOW OPTIMUM ABOVE OPTIMUM VERY LOW LOW OPTIMUM ABOVE OPTIMUM
Broadcast and Incorporate in fall 40 150 100 25-50 0 150 100 50 0
Sidedress in spring when shoots are 6 inches high 40 0 0 0 0 0 0 0 0

Sidedress 3-4 weeks later 

40

0

0

0

0

0

0
TOTAL RECOMMENDED 120 150 100 25-50 0 150 100 50     0

Planting

Garlic is planted in the fall since it requires a cold temperatures to induce bulb formation. Planting typically occurs from October in northern New England to early November in southern areas. The goal is to time planting for good development of roots, but not enough time for the shoots to emerge from soil before winter (6-8 weeks before the grouns freezes). Many different planting arrangements are used by growers depending on irrigation, mulching, and weed control systems. Planting cloves too densely can reduce bulb size, while spacing too far apart reduces yield per area of land. Common planting arrangements include 2-row beds 30" apart on center with 6" spacing in- and between-rows, 3- or 4-row beds with 6-8" in- and between-rows, single rows spaced 24-30" with 6" in-row spacing. Wide row spacing between rows allows for easy mechanical cultivation for weed control; planting multiple rows per bed allows for use of plastic mulch to control weeds.

Garlic varieties differ in size and weight of cloves; generally, there are about 50 cloves in a pound. Large cloves tend to produce the most vigorous plants and largest bulbs; therefore, small cloves are often not planted. Bulbs should be separated no more than a day or two before planting so they do not dry out. Cloves should always be planted with the root side down, 3-4" deep, and so the top of the clove is 1" below the soil surface. Plant only healthy-looking cloves to avoid disease and pest problems.

Field Culture 

A layer of clean straw mulch is typically applied to garlic at planting to avoid drastic soil temperature fluctuations and heaving in the winter and early spring. The garlic will grow through the mulch in the spring. Alternatively, garlic can be planted into plastic mulch. Either will conserve soil moisture and suppress weeds. It may be advisable to remove straw mulches in very wet springs to allow soil to dry out and thus reduce the threat of soil borne diseases. In very cold growing areas, removing mulch can also speed soil warming and garlic growth in the spring. Because garlic is shallow-rooted, irrigation is very beneficial during dry periods. 

Clipping scapes from hardneck garlic once fully curled, just below the curl, has been found to improve bulb size. Scapes are edible, and can be sold and used as a garlic-flavored fresh vegetable similar to scallions.

Harvest and Storage

Although variable depending on variety and growing conditions, 1 lb of garlic 'seed' bulbs will usually yield 4-8 lb at harvest. Garlic may be ready to harvest over several weeks during July. When the lower third of leaves turn brown, it is advisable to pull several bulbs to check for maturity. Cut the bulbs in half width-wise, and check whether cloves have fully filled out within the skins or if there are gaps indicating they still have some room to grow. When no gaps remain and the cloves have filled their skins, they are ready to harvest. Gently pull, dig, and/or undercut the bulbs to remove them. Unless a lot of soil is adhered to the bulbs, they do not need to be washed at harvest (although some markets may demand it). Place the harvested plants on wire racks or tie in bundles for hanging and cure for several weeks in a dry area with good ventilation. Curing takes 10-14 days. Stems may be cut before or after curing. Curing is complete when the outer skins are dry and crispy, the neck is constricted, and the center of the cut stem is hard. After curing, tops can be cut to leave about an inch remaining, and roots should be trimmed closely. If necessary, bulbs may be brushed or the outer skin gently rubbed off to clean them.

For long-term storage, garlic is best maintained at temperatures of 30 to 32 °F with low RH (60 to 70%). Good airflow throughout storage containers is necessary to prevent any moisture accumulation. Under these conditions, well-cured garlic can be stored for 6-7 months. Storage at higher temperatures (60°F) may be adequate for the short term, but it is important to select a place with low relative humidity and good air flow. As with onions, relative humidity needs to be lower than for most vegetables because high humidity causes root and mold growth; on the other hand, if it is too dry the bulbs will dry out.

Seed.  Garlic bulbs that are to be used as seed for fall planting of next years’ crop should be stored at 5 °F and at relative humidity of 65-70%. Garlic cloves break dormancy most rapidly between 40 to 50°F, hence prolonged storage at this temperature range should be avoided. Storage of planting stock at temperatures below 40°F results in rough bulbs, side-shoot sprouting (witches-brooms) and early maturity, while storage above 65°F results in delayed sprouting and late maturity.

Garlic cloves used for seed should be of the highest quality, with no disease infections, as these can be spread to new fields and to next years’ crop.  Be on the lookout for garlic blight nematode which may have been distributed around New England on infested seed garlic.  This nematode, which is also known as a bulb and stem nematode, causes bloated, twisted, swollen leaves, and distorted and cracked bulbs with dark rings. Infestation with this nematode can weaken plants, causing them to be susceptible to secondary infections.