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Last revised February 5, 2010
Note: Information specific to the production of garlic for planting stock or dehydration is found in the file Garlic for Production of Planting Stock.
Most of the garlic grown in the Pacific Northwest is the non-bolting (soft-neck) type, typically strains of California Early and California Late. The information that follows in the next two sections "Growth and Development" and "Climatic Requirements" is from work done on a number of varieties by various researchers over the years, and has been selected to relate primarily to the temperate region garlic (bolting and non-bolting types) grown here. The most important references relied on are those by L. K. Mann and Y. Yamada in the 1950s and 1960s, and the exhaustive review of literature on garlic that is found in the three-volume Onions and Allied Crops edited by H.D. Rabinowitch and J.L. Brewster, CRC Press, 1990.
Photo credit: Alex Stone, Oregon State University
TYPES OF GARLIC
Two species, Allium sativum (domestic) and A. longicuspis (wild) of garlic are recognized. They are so similar visually that these species distinctions are not generally used. A more useful distinction is the classification of garlic into softneck and hardneck types. All wild garlic is of the hardneck type but domestic garlic may be either hardneck or softneck. Both begin with leafy tissue in spring but hardneck garlic will produce a seed stalk in late May or June.
Hardneck garlic is represented by varieties such as Roja, German Red, and Valencia. Continental garlic may be purple striped or white, and includes many of the southern varieties. Creole garlic is the type grown in Mexico, South America and the Imperial Valley of California. It is covered with a deep purple skin, is quite late and is not suited for production in the Pacific Northwest.
With some of these varieties, seedstalks may often be topped with a cluster of small capsules called bulbels (also referred to as bulbils, topsets or, erroneously, bulblets). Although bulbels are sometimes used to produce small garlic bulbs, the seedstalks should be removed as they appear in order to minimize yield reduction of the crop. The term bulblet is more correctly applied to the small round bulbs embedded in the scales of, or attached to the large main bulb of certain cultivars and types. Bulblets are especially common in elephant garlic.
Softneck garlic is also referred to as Silverskin, artichoke, or Italian. Softneck types are best represented by the varieties California Early and California Late (also categorized as artichoke types). Silverskin garlic may also be differentiated into many-cloved or few-cloved varieties, and may also be tan, all white, or purple tinged. Numerous strains exist, having been selected over the years by the various companies that produce them for dehydration (Creole), or growers producing them for fresh market. Silverskin garlic rarely, if ever, produces seedstalks.
Further general classifications (each with its own group of varieties or strains) include: Rocambole, Continental (eastern European), porcelain and Asiatic (all hardneck types).
Elephant garlic (Allium ampeloprasum) is not a true garlic but a type of leek that produces very large cloves, often only 3 or 4 per bulb. Several small bulblets may also develop. It produces a large seedstalk that may be cut and sold to florists! The tenderer, fleshy lower portion of the seedstalk is also prized for stir-fried Oriental dishes. Elephant garlic is not generally used for dehydration, but is becoming popular for "medicinal" purposes. Flavor is milder than garlic and can be slightly bitter. The fresh market product is sold mainly through farmers' markets or through specialty produce stores or specialty sections of produce supermarkets. More recently, sales to specialty processors for medicinal or health food use have increased.
General Descriptions of Garlic Types
Rocambole, serpent, or Bavarian garlic, sandleek, Spanish shallot and top-setting garlic. Their distinctive flower stalks form a coil after they emerge. Blotchy-purple coloration on wrapper leaves, cloves brownish sometimes reddish. Cloves arranged in a circle around the flower stalk and are full flavored.
Roja: Symmetrical, attractive, uniformly colored brownish-red, medium-sized bulbs. Commonly grown by gardeners.
Continental: Purple-striped, symmetrical bulbs. Some purple coloration of cloves.
Porcelain: Tight, paper-white, shiny wrappers. Plump, large cloves.
Asiatic: Uncommon in the northwest. Cloves plump and well defined. Bulbs usually well colored. Skins often very thick. Bulbels often dark purple.
California Early and California Late. The most common commercial garlic grown in the Pacific Northwest and California. Many selections and strains developed by dehydration companies for their own use in dehydration. Some also used for fresh market. Synonymous with "artichoke" garlic.
"Silverskin" types: Similar to California types above except bulbs have more but smaller cloves. Adapted to colder areas of the Northwest. Numerous strains grown by gardeners.
Many other less common "gourmet" garlics are available in limited quantities. The Garlic Store has an extensive listing of garlic and other alliums.
GROWTH AND DEVELOPMENT
Information from various publications indicates that:
* Matured garlic cloves, planted in the fall, go through a short (about 2-week) dormant period. With adequate moisture and temperature (see below), roots emerge and leaves sprout, and the plant goes through a period of vegetative growth. With the onset of winter, the plant undergoes vernalization (induced to bulb and flower) by low winter temperatures.
* Although vernalized, no inflorescence or lateral buds (that later form the bulb) are developed until early spring with the onset of lengthening days and suitable temperatures. Proper bulbing is a function of adequate growth, vernalization, and subsequent growth under long days.
Some temperate-region varieties may be adapted to spring planting because the long photoperiod of northern temperate regions are adequate, even if only minimal cold treatment has occurred. The degree of bulbing and flower stalk formation varies considerably and with genotype. From a flowering standpoint, three classifications are reported:
1. Non-bolting types. These do not form flower stalks, or do so only rarely. Only primary cloves form (as in strains of California Early and California Late).
2. Incomplete bolting types. These usually produce a flower stalk, the terminal of which (the bulbils) often remains enclosed in the pseudostem. Some of these types form a second set of cloves within the primary cloves, and may be confused with non-bolting types.
3. Complete bolting types. These bolt readily, producing a scape that terminates in an inflorescence containing sterile flowers and topsets (bulbils).
The relationship between temperature and photoperiod is complex and variety dependent. Generally, a photoperiod longer than a critical value is the main factor inducing storage leaf formation after a period of cold treatment. Also, the longer the cold treatment, the shorter the critical photoperiod required for storage leaf induction (and subsequent bulb formation).
A garlic bulb develops from the bud primordia (2 or 3) of the cloves that are planted. Each bud primordia forms between two and six growing points, each of which develops a lateral bud which later develop into a clove. Temperatures during growth determine the rate of leaf growth, clove, and flower stalk development. Clove formation in non-bolting types differs slightly in that lateral-bud primordia (which form the cloves), form in the axil of the youngest 6-8 foliage leaves, beginning with the oldest one. At maturity, these develop into cloves. The growing point may then either form a clove and go dormant, or form an incomplete leaf that degenerates.
A garlic bulb can therefore be best described as an aggregate of cloves surrounded by a sheath consisting of the basal portions of one or more mature dry leaves. Each clove consists of a vegetative bud and two modified mature leaves. The inner of these two leaves forms a thickened base that makes up the clove. The base of the outer leaf forms the dry sheath surrounding the clove. The blades of both these leaves abort just above the clove. The vegetative bud is imbedded in the clove and consists of one or two leaf initials.
Garlic grown in temperate regions such as the Pacific Northwest is responsive to temperature and photoperiod for proper clove and bulb formation (and subsequent seedstalk development of some varieties). Varieties adapted to southern latitudes, that bulb under the temperature and short day conditions common to those latitudes, may not bulb or segment properly in the Pacific Northwest.
With varieties such as California Early and California Late, a period of cold exposure is needed for proper bulbing and clove development. That cold treatment is thought to be about 6 to 8 weeks of a mean temperatures below 40 F but may be considerably shorter with some strains. Garlic may be sensitive to a cold treatment range of between 32 and 50 F and is sensitive either during growth or while the cloves are in storage. Photoperiod interacts with temperature so that cloves held in cold storage will bulb quickly when planted in spring (increasing photoperiod) resulting in small bulbs.
Bulb and clove size is related to the amount of vegetative growth that takes place before bulb and clove initiation occurs. This determines optimum clove storage temperature, planting date and associated growing temperatures and changing day length.
Cloves exposed to adequate cold treatment may have a reversion of vernalization under water stress and high temperatures (above 85 F) so normal bulbing does not occur. The longer the cold treatment, however, the more difficult it is to devernalize the plants. Also, plants that are growing rapidly with good soil moisture are less susceptible to devernalization.
Planting equipment for garlic is specialized and often custom built. A Canadian company which manufactures a planter suitable for garlic and shallots is BDK Fabrication, 240 Argyle St., Delhi, Ontario N4B 2W8. The contact person is Mr. Don Haskins, 519-582-8348. BDK Fabrication also manufactures single and multiple-row garlic harvesters. For small acreage plantings, a potato attachment designed to be used with a Holland Transplanter may be suitable for use. Contact the Holland Transplanter Co., 510 East 16th St., Holland, MI 49423-0535. Another machine is the Model 4000 carousel plug transplanter from Mechanical Transplanter Co., 1150 S. Central Ave., Holland, MI 49423. Cloves must be individually hand-fed in the latter machine.
Silver skin garlic cloves should number approximately 75-80 per pound, while elephant garlic cloves may be up to 4 ounces each. Clove sizes will vary from year to year as production conditions affect bulb sizes, quality and yields.
Garlic for seed purposes should not be stored under refrigeration. When necessary, store garlic for seed at 50 F and maintain a humidity of 65-70%. Garlic cloves sprout most rapidly at 40 to 50 F, hence prolonged storage at this temperature range should be avoided. Storage of planting stock at temperatures below 40 F may result in rough bulbs, side-shoot sprouting and early maturity, while storage above 65 F may result in delayed sprouting and late maturity.
Extreme care must be exercised in using pest-free planting stock. Bulbs and cloves used for planting can carry and transmit diseases such as Sclerotinia cepivorum (white rot), Fusarium cumorium, (basal rot), and possibly Botrytis allii and B. porri. The seed may also be infected by Penicillium, a fungus that can cause a decay of the seedpieces and reduce stand. Other important pests that can be carried on the seed stock are several species of nematode (stem and bulb). Some of these pests may render the soil unusable for further production of garlic, onions and related crops. Whenever possible observe the field from which the planting stock is to be obtained for these and other pests. See also the section on disease and insect control.
Garlic should be planted in early fall (September or early October). Data from California indicate that higher yields are associated with earlier fall plantings (comparing October and November plantings). Although plantings have been made successfully in late winter (February or March), under certain conditions these later plantings may not bulb properly if growth and cold induction has not been sufficient before bulbing begins in May.
Plant cloves about 2 inches deep. Select healthy large cloves, free of disease. Medium cloves may generate the best economic return due to the increased count per pound and reduced number of pounds required for planting. Cloves that are small may not segment adequately.
For ease of digging, and to reduce soil compaction, garlic is often grown on raised beds that are prepared in the fall. Beds are usually 40 inches apart center to center, with 2 rows of garlic grown on top of each bed. Rows are spaced 12 inches apart.
Silver-skin garlic is planted at about 6-8 cloves per row-foot (12-16 plants per bed-foot) for California Early and 8-9 cloves per row-foot (16-18 plants per bed-foot) for California Late. This should produce a population of about 100,000 to 150,000 plants per acre. From 1600 to 2000 lb of California Early, and 1400-1700 lb of California Late cloves are needed to seed an acre. The higher populations are used for processing or planting stock purposes. Elephant garlic is planted at 2-4 cloves per bed foot requiring 500 to 1000 lb of cloves per acre.
Garlic will grow in almost any well-drained, friable soil, preferably with good organic matter content. These soils allow the bulbs to expand without becoming misshapen. It will also aid in the soil water holding capacity, which is important due to the relatively restricted rooting characteristic of garlic. Soils must have a pH above 6.0. Ideal pH is between 6.5 and 7.0
The following are general recommendations. It is advisable to submit a soil test for each field being planted.
Nitrogen, Fall-Planted Garlic
Apply 50-75 lb N/acre in the fall. Band the fertilizer 4-5 inches below the soil and 1-2 inches to the side of the row together with the needed P (see below). Care in the timing of N applications is important. Witches-brooming is believed to be caused by heavy manuring or extended periods of high soil N levels during the short days of winter, lasting for about one or more months, and starting just before lateral-bud formation.
In the spring, apply 100-175 lb N/acre split into 2 or 3 applications as plants begin to grow. See also the comments in the section on N liquid fertilizers having herbicidal effects:
Nitrogen, Spring-Planted Garlic
Since spring planting results in smaller bulbs, use 100-150 lb N/acre depending on soil type and variety. Apply 1/4 of the N and all the P and K at time of planting and the remainder of the N when the garlic is 6 inches tall. See also the comments in the sections below on N liquid fertilizer formulations having herbicidal effects, and recommendations for P and K.
For N liquid fertilizer formulations for weed control in garlic and other alliums, see the file Nitrogen Fertilizer Solutions Providing Ancillary Weed Control in Alliums
Base P application rates on soil test. Usually, 100-200 (P2O5) lb/acre. All P should be banded at planting time.
Base K application rates on soil test. Usually, 0-150 (K20) lb/acre. Broadcast before planting.
Apply lime, as indicated by soil test to bring pH above 6.0, preferably between 6.5 and 7.0. Calcium deficiency can result in soft, watery cloves that appear paper-like when the bulbs are dry and mature.
Apply micronutrients only as indicated by soil test.
No irrigation is necessary in fall after planting if soil moisture was adequate at planting depth. If not, one irrigation may be needed to establish the planting.
In spring, keep garlic growing actively. From 6-10 inches of water may be necessary in western Oregon in late spring and summer. Approximate summer irrigation needs for the Hermiston area have been found to be: 3.5 inches in May, 5.0 in June, 7.5 in July, and 7.0 in August. Water stress during clove development has been implicated in witches-brooming.
Continue irrigation until cloves are well filled and bulbs are the desired size. Examine bulbs regularly as harvest date approaches for presence and condition of the scales surrounding the bulb. Terminate irrigation when there are 2-3 matured scales surrounding the bulb. If irrigated too long, these scales will deteriorate one at a time until there are none, causing bulbs to shatter at harvest. Garlic should not be irrigated once the tops begin to fall and become dry. In the Willamette Valley, irrigation is usually discontinued around mid to late June for California Early garlic and around July 4 for California Late Garlic.
Mid-May to mid-June is a critical period for Botrytis gray mold. Exercise care in disease control and irrigation.
Soil type does not affect the amount of total water needed, but does dictate frequency of water application. Lighter soils need more frequent water applications, but less water applied per application.
Some types of garlic produce flower stalks with small aerial bulbils. Removal of these stalks enhances crop maturity and yield. Research in Colorado and Washington indicates that crop yields (average bulb weights) can be dramatically increased (70%) by removing these flower stalks soon after they develop.
HARVESTING, HANDLING, AND STORAGE
Depending on the type of garlic being produced, yields can range from 5,000 to 17,000 lb/acre. Yields are dependent on planting date, plant population and planting stock size and quality. Yield of elephant garlic, which is normally planted at low plant populations, can range from 1,000 to 6,000 lb/acre. Garlic is ready for harvest when the tops become partly dry and bend to the ground.
Although garlic can be harvested several ways, single or multiple-row harvesters are avialable or can be custom built.
Fresh Market: Garlic intended for braiding or fresh market may be harvested at an earlier stage (some green color still remains in leaves) to allow for some peeling and braiding. To loosen the bulb, run a cutter bar beneath the bulbs. Rows may be windrowed in the same operation using modified potato equipment. If garlic is to be hand harvested, pull the bulbs and gather several rows into one windrow. If tops have not already been removed, arrange the tops to protect the bulbs from sunscald if the un-topped windrow is to be cured in the field. If left in the field to dry, remove tops and roots after they are dry and prior to storage. Leave about 0.5 inch of root and 1 inch of top. Bulbs must then be graded for market.
Garlic for processing: After the tops have dried they may be partially removed by propane flaming. Care should be exercised so that garlic bulbs are not exposed and subjected to flaming damage. Flailing is used to complete top removal. Garlic may be dug with a simple potato digger and windrowed on the soil surface for a brief (1-2 day) curing period, then hand placed into sacks or bins for final curing (10-14 days, or as needed) in the field. Garlic must be protected from sun scald especially during periods of high temperature (over 90 F) and bright sunlight. Excessive exposure to sunlight may also result in greening.
If bulbs tend to shatter, or if wrapper leaves discolor, late watering may be the cause (see irrigation section above). Other causes of shatter may be stem and bulb nematode infestation or too rapid drying of the bulbs after harvest.
STORAGE (Quoted or modified from USDA Ag. Handbook 66 and other sources)
Garlic for seed purposes should not be stored under refrigeration. Optimum storage temperature for garlic for seed is 50 F with a humidity of 65-70%. Garlic cloves sprout 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 result in rough bulbs, side-shoot sprouting (witches-brooming) and early maturity, while storage above 65 F results in delayed sprouting and late maturity.
Store other garlic at 32 F and 65 to 70 % relative humidity. If in good condition, and well cured when stored, garlic should keep for 6 to 7 months at 32 F. Relative humidity should be lower than for most vegetables because high humidity causes root and mold growth. In California, where considerable garlic is grown, it is frequently put in common storage, where it can be held for 3 to 4 months or sometimes longer if the building can be kept cool, dry, and well ventilated.
Fresh market garlic is commonly packaged in cartons, holding 12 display cartons of 1 dozen each; 10-lb cartons holding 12 tube or vexar mesh bags; packages (2-3 bulbs per package); or, 30-lb telescope bulk cartons.
Elephant garlic may be packaged as above, or in 5-lb or 10-lb cartons or various count bags of sized cloves as follows:
Clove size Bag count Bag count 5-lb carton 10-lb carton 8 cm 16-18 32-36 9 cm 13-14 26-28 10 cm 9-11 18-22 11 cm 7- 8 14-16 12 cm 5- 6 10-12
Garlic imported from Chile is packaged in 22-lb (10-kg) cartons.
Fresh Market Vegetable Production, Garlic