Garlic

Introduction

Garlic (Allium sativum) 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 and often develop better flavor in cold climates. 

Types and Varieties

There are two main types of garlic: hardneck and softneck. Hardneck (or topset) garlic produces false flower stalks called scapes, which are also edible. It typically has about 6 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 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, garlic variety names should be taken with a grain of salt. As with other vegetatively propagated crop plants, insect pests and diseases can be carried over from one generation to the next. It's a good idea to start out with several different varieties, selecting and saving seed from those that perform best and appear to be free of pests. It is also recommended to buy seed from reputable sources that test their stock for several serious seedborne pests and diseases (including bloat nematode, white rot, and Botrytis neck rot).

Soil Fertility

A well-drained soil with good tilth and 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 6–6.8. 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 twice in the spring, about a month apart, will produce optimal yields. Do not apply nitrogen once plants begin bulbing, as this can increase foliar growth at the expense of bulb development.

Plant Nutrient Recommendations According to Soil Test Results for Garlic

Planting

Garlic is planted in the fall since cold temperatures are required to induce bulb formation. Planting typically occurs from October in northern New England to early November in southern New England. 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 ground 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 acre. Plants are commonly arranged in beds with 3–5 rows each, spaced 6"–12” apart. Wider plant spacings also allow for better airflow, which can reduce foliar disease.

Garlic varieties differ in size and weight of cloves; generally, there are about 50 cloves in a pound. Large cloves with large basal plates 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 although it will still benefit from an insulating straw layer over winter to avoid frost heaving cloves to the surface. Straw can be raked back in spring to warm the soil. Both mulch options 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 soilborne 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, typically by about 15%–20%. Scapes are edible, and can be sold and used as a garlic-flavored fresh vegetable similar to scallions. The decision to remove scapes should weigh the labor involved in harvesting, the market for scapes, and the potential increase in bulb size.

Harvest and Storage

Although very dependent on variety and growing conditions, 1 lb of garlic 'seed' bulbs will 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 wrapper leaves. When no gaps remain and the cloves are fully developed, they are ready to harvest. Undercutting plants greatly aids in pulling up bulbs. Handling bulbs gently is critical, as any damage created in the harvesting or post-harvest processes create entry wounds for pests and diseases. 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). Do not leave bulbs in full sun because high temperatures (above 120°F) result in waxy breakdown, a physiological disorder that renders bulbs unmarketable. 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 1" remaining, and roots should be trimmed closely. If necessary, bulbs may be brushed or the outer skin gently rubbed off to clean them.

Table stock: For long-term storage, garlic is best maintained at temperatures of 30°F–32°F with relative humidity of 60%–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 stock: Garlic bulbs intended for use as seed should be stored at 55°F–60°F and at relative humidity of 65%-70%. Garlic cloves break dormancy most rapidly between 40 and 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 ("witch's broom") 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 firm wrappers and no apparent defects, as pests and diseases can spread to new fields and the next year's crop. If saving seed, consider submitting a sample of plants for a seed garlic test (University of Maine Plant Disease Diagnostic Lab) to ensure the the lot is free of several major and persistent pests.