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Garlic Production
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IntroductionGarlic has been used as food, a condiment, and for medicinal purposes for over 5,000 years. It is thought to have originated in central Asia, and then later brought to the Mediterranean area. Garlic (Allium sativum) belongs to the Amaryllidaceae family. Mild flavored elephant garlic (Allium ampeloprasum) is not a true garlic and belongs to the same species as leeks. Ontario imports a substantial quantity of fresh and processed garlic products mainly from the USA, Mexico, and South America. Garlic powder is the most popular form of dried garlic with dehydrated pieces, flakes, and garlic salt also used. The majority of Ontario grown garlic is sold to the fresh market as whole fresh bulbs. Green tops of garlic, garlic spreads, and chopped garlic are also sold to a lesser extent. There are no garlic dehydration facilities or organized marketing structure for selling or for distribution of garlic in Ontario. There is however, a producer organized Garlic Growers'Association of Ontario. | Top of Page | Plant Growth and DevelopmentGarlic is a perennial plant, commonly grown in Ontario as a winter annual, planted in fall and harvested the following summer. Garlic bulbs are composed of a number of thick, modified storage leaves called cloves, which are used as planting stock. Cloves planted in late summer or fall develop extensive roots before winter, with little or no visible shoot growth. Overwintering shoot growth above the soil surface is not desirable, since it will be prone to winter injury in areas of insufficient snow protection. Properly planted, healthy cloves are very winter hardy.
Figure 1. December removal of October planted garlic cloves showing late fall root development. A strong, well-established overwintering plant will rapidly develop shoot growth during spring as soil and air temperatures increase. With adequate moisture and nutrition, a large plant will develop before bulbing takes place. Many strains of garlic require a cold period to initiate bulbing. Fall-planted garlic receives a natural cold period as it overwinters in the soil. Spring-planted garlic, however, may require cold storage prior to planting to allow proper bulb development. The bulbing response is stimulated by the long days and warm temperatures of late spring. During this time, "hardneck" strains of garlic produce a solid flowering stalk referred to as the scape. The scape does not produce true seed, but rather develops small vegetative bulbils, also called bulblets, pips or topsets. There is considerable variability in the size and number of bulbils produced by "hardneck" garlic. Bulbils may be used as planting stock, although they often require two or more years of growth to develop into marketable bulbs. Early removal of the scape during its development results in increased bulb yields. "Softneck" strains of garlic do not produce a scape. Each of the cloves, which make up the complete bulb, develops from an auxiliary bud at the leaf base. The leaves which are most exterior on the growing shoot form the sheath leaves which protect the bulb. Bulb size increases during late spring and summer until the leaves of the plant begin to dry, turning tan brown from the tips toward the base of the leaves. As the bulbs increase in size, they also increase in dry matter content. After harvest further drying is required to cure the bulbs. Once cured, bulbs are ready for long-term storage. Garlic left in the field unharvested will begin to develop new root growth from each of the cloves during late summer.
| Top of Page | VarietiesThere are an enormous number of strains of garlic in the world, with few strains being named as cultivars. Current strains of garlic grown in Ontario originate from Asia, Europe, Northern Africa and North and South America. Cultivated garlic plants do not produce true seed. Therefore, no crossing or exchange of genetic material occurs between strains of garlic. All garlic is propagated vegetatively from cloves and bulbils, with each clove or bulbil a clone of the parent plant.
Figure 2. A "hardneck" garlic strain showing early summer scape development.
Figure 3. Bubils produced on scape tops vary in size and colour depending upon the strain of "hardneck" garlic. Two types of garlic, described as "hardneck" and "soft-neck", are grown in Ontario. Hardneck garlic strains bolt during late spring, producing a tall, solid flowering scape which protrudes through the center of the bulb. A small proportion of the scape remains with the marketed bulb of hardneck strains. Softneck garlic strains in Ontario do not develop a scape and generally have larger number of cloves, and smaller cloves per bulb than hardneck strains. The softneck strains are better suited to mechanization; the outer bulb sheath leaves can be brushed off mechanically. Garlic bulbs vary in color from red to white; clean, white garlic is preferred by the fresh produce market in Ontario. Most garlic growers save their own locally adapted garlic bulbs for planting stock, and usually obtain new planting material from other local growers. | Top of Page | Location and Soil PreparationGarlic can be grown successfully on a wide range of soil types and is grown in most cultivated areas of Ontario. Soils which are prone to excessive frost heaving are least desirable. Enhanced plant survival has been observed in areas where good snow cover occurs and fields should be chosen accordingly. Fields should be selected which provide ample wind protection, especially where garlic is to be planted in lighter soils. Soils with high organic matter content are preferred due to their increased moisture- and nutrient-holding capacity. Soils containing sufficient organic matter are also less prone to crusting and compaction. Very heavy soil types hinder bulb expansion, especially if allowed to dry out, resulting in rough and irregular shaped bulbs. Intensive soil manage-ment practices are required on light sandy soils due to their low moisture-holding capacity. The soil should be prepared far enough in advance in order to eliminate perennial weeds, adjust pH, nutrient and organic matter levels if needed, and remove any soil obstructions. The greatest success has been achieved where the soil pH ranges from 6.0 - 7.5. Any necessary pH adjustments should be made prior to planting. pH levels below 6.0 have resulted in winter injury, poor plant vigour, reduced plant stands and overall yield reduction. For any crop, efficient use of fertilizer is dependent upon proper soil pH levels. The organic matter content of the soil should be built up before planting to increase the manageability of the soil. Organic matter can be increased by applying well-rotted manure or by plowing down a green manure crop. For further information on green manure and cover crops, see OMAFRA Publication #363, Vegetable Production Recommendations. Before planting, the soil should be worked deep enough to present a consistent planting medium that allows easy insertion of cloves into the soil. | Top of Page | Clove Preparation for PlantingGarlic seed stock should be stored as whole bulbs until shortly before planting, since cloves separated from the parent bulb deteriorate more rapidly than whole bulbs. Break apart or "crack" the bulbs just prior to planting. Dry bulbs are more easily broken apart into cloves than damp bulbs. Either hand or mechanical equipment is commonly used to break the bulbs apart. However, there is greater potential for physical damage to cloves when using mechanical cracking devices. Some mechanical planting equipment requires that cloves be graded into sizes or weight ranges for improved planting efficiency. Any damaged or diseased cloves should not be planted. When planning to use your own planting stock, harvest the planting stock bulbs later than your main crop. Harvesting very mature bulbs increases the ease of clove separation prior to planting. Planting larger cloves of the same strain of garlic will produce larger bulbs than the planting of smaller cloves. Many garlic seed treatments intended for crop protection and disease reduction have been tested. To date, no registered seed treatments have proven to give consistent beneficial results. The most consistent success has been achieved by planting healthy, damage- and disease-free planting stock. | Top of Page | Planting and SpacingCurrent research suggests that the optimum planting date is between September and November. Early spring planting may also be successful, although bulb yields tend to be lower and increased storage losses of planting material are common. To estimate the planting date, use the average date of first fall frost as listed in OMAFRA Publication #363, Vegetable Production Recommendations. This will provide an approximate planting date for your area. The amount of planting material required will vary from 700 - 1000 kg/ha, depending upon the weight of individual cloves planted and the spacing used. The average number of cloves within each bulb varies from less than 8 to greater than 15 depending upon the strain of garlic. Space plants 7 - 12 cm apart in the row. Cloves of small-bulbed strains may be planted as close as 7 cm apart, while large-bulbed strains will require as much as 12 cm between plants. Spacing between rows will depend on the method of planting and available equipment for cultivation. Single or multiple rows of plants are commonly used, with spacing between rows generally not less than 20 cm. Plant cloves so that the distance from the soil surface to the top of the clove is 3 - 5 cm. The 5 cm planting depth is recommended for light or organic soils. Cloves planted too shallow are prone to injury during the winter and early spring. Garlic which is planted in the spring may be planted closer to the soil surface. Hand planting is the traditional method of planting garlic, however, several imported mechanical planters are now in use. Various home-built or modified mechanical planters have been tried with only moderate success. | Top of Page | FertilityGarlic grows well on fertile soils. The soil phosphorus and potassium levels should be determined by a soil test. Any phosphorus or potassium required should be broadcast followed by shallow incorporation into the soil before fall planting. The total amount of nitrogen required will vary with the soil type, the previous crop grown, the amount of organic matter present and the climatic conditions during the growing season. Garlic will generally require 70 - 125 kg/ ha of nitrogen. A small amount of nitrogen can be applied in the fall. One half of the nitrogen should be applied as soon as the garlic begins to grow in early spring; the remainder should be split into two to three applications at three week intervals. The application of nitrogen should be completed within 4 - 6 weeks of harvest. Nitrogen can be applied through irrigation, although care must be taken to avoid foliar burn. The preferred sources of nitrogen are calcium or ammonium nitrate. Applications of urea should be avoided due to potential plant injury. | Top of Page | IrrigationGarlic is sensitive to moisture stress throughout the growing season. Any periods of dry soil conditions, especially during bulbing, will result in yield reductions. For most soils, approximately 2.5 cm of water per week is required during the growing season. In sandy soils, however, 5.0 cm or more of water may be required during hot, dry weather conditions. The preferred time of irrigation is morning to mid-afternoon, thus allowing sufficient time for the plant foliage to dry before nightfall. As garlic becomes mature at harvest, irrigation should cease. This cultural practice increases harvesting ease and reduces the potential deterioration and staining of exterior bulb sheath leaves. | Top of Page | Weed ControlGarlic is a weak competitor against vigorous weeds. Therefore, weed control is essential and can be undertaken by cultivation, hand-hoeing or with herbicide application. Deep cultivation close to the plants should be avoided as root damage with subsequent yield losses may occur. For up-to-date weed control information, consult OMAFRA Publication #75 Guide to Weed Control. | Top of Page | Insects and DiseasesThe major disease problems of garlic in Ontario are: Fusarium basal rot, Penicillium mould, and viruses. Fusarium basal rot is a disease which attacks the basal plate region and the roots. The soil-borne pathogen invades the roots, resulting in empty, tan-colored, non-functional roots. The basal plate region may develop a pinkish growth of mycelium. First visual symptoms are often the yellowing of the tip and dieback of the shoot during the spring. Warm soil temperatures and high soil moisture promote disease development. Since the Fusarium inoculum remains as dormant spores in the soil or on plant residue, crop rotation with crops not belonging to the Allium genus (e.g., garlic, onions, shallots, leeks, chives) is recommended. Penicillin mould is a main cause of decay of garlic in storage. The disease appears as masses of blue-green spores usually first seen at the base of the bulb. The primary source of inoculum is diseased bulbs used for planting material. When diseased bulbs are cracked the air-borne spores readily come in contact with healthy cloves. Wounded cloves are particularly susceptible to the disease. Often cloves infected with Penicillin become infected with secondary organisms such as bacteria and other fungi, masking the original pathogen. Clove rot and reduced plant stands are often the result of planting infected cloves. Surviving plants which emerge appear weak and yellow. Warm temperatures of 22 - 25 °C are optimum for spore germination and disease development. Planting garlic too early in late summer when soil temperatures are high may increase the severity of clove rot. Irrigation may be beneficial, as high soil moisture appears to suppress clove decay. Virtually all sources of garlic contain viruses. Fortunately, most of these viruses in garlic are latent. Latent garlic viruses may not become visible or reduce yields until the garlic plant is stressed or growth interrupted. The most common symptoms of virus infection are colour changes of the leaves. These include mosaics, flecking, streaking and mottling. Leaf shape distortion may also occur. Aphids are one vector capable of transmitting some viruses from infected to healthy plants. Control of virus diseases is achieved through a combination of planting healthy cloves, reducing aphid populations, proper fertility and water management during the growing season. The major insect problems in Ontario include onion maggots, thrips and wireworms. There are, at present, registered insecticides that will control these pests. Consult OMAFRA Publication #363 "Vegetable Production Recommendations" for information on registered insecticides and control procedures. Bulb and stem nematode and white rot are very serious problems of garlic production in other areas of the world. Once these problems are established in a field, control may be difficult or economically unfeasible. Garlic and onions are closely related, therefore, Agriculture Canada Publication #1716, Diseases of Onions in Canada, should be helpful. | Top of Page | Harvesting and GradingHarvesting begins when the leaf tops begin to dry, discolor and bend
towards the ground. Another indication of bulb maturity is the reduced
thickness of the sheath leaves surrounding the bulb. Early harvest results
in bulbs which are immature and tend to shrivel when cured, while late
harvest may result in bulbs which have stained, partially decayed wrapper
leaves and exposed cloves. Figure 4. Hand-harvested garlic bulbs ready for curing. With small plantings of garlic the bulbs are usually harvested by hand pulling, using a fork to loosen the soil and facilitate lifting. On larger plantings a tractor drawn blade is commonly used to loosen the soil under the bulbs. A mechanized system can be used to lift the bulbs, remove the tops and separate the dirt and trash from the bulbs, however, complete mechanized harvesting is not used in Ontario at the present time. Once harvested, the garlic must be cured properly to ensure a long storage life. Field curing is achieved by placing the harvested garlic in covered, slotted vegetable bins and allowing natural air drying. Curing is often accomplished indoors using forced air to dry the bulbs. Garlic cured indoors should either be placed in slotted bins, on wired racks or on open trays in a well-ventilated building.
After curing, the garlic should be trimmed. Both the tops and the roots should be removed. Topping and root trimming are done mechanically or by hand. Brushing to remove the loose outer sheath is the final step before marketing. Garlic imported into Canada is commonly graded by size, with the larger-sized bulbs commanding a higher price. Grading is done by hand or mechanically. The grade sizes used are as follows:
| Top of Page | StorageFor maximum storage life, garlic should be properly cured and stored at 0 °C with a 60 - 70% relative humidity. Higher humidity provides excellent conditions for the development of Penicillin mould and root growth, which is undesirable. Adequate air circulation and proper storage containers are important to remove transpired heat and moisture. As storage temperatures are increased above 0 °C, the rate of bulb weight loss also increases. Storage life under appropriate conditions is 5 - 8 months depending upon the strain of garlic. | Top of Page | MarketingPresently, the majority of Ontario-produced garlic is marketed as fresh product to wholesale distributers, independent grocers, farmers' markets or at the farm gate. Economics of scale do not support a processing industry at this time. However, processing alternatives may become a reality as the industry grows. To increase profitability, many producers have used value added techniques such as braided, pickled or home-processed garlic. Scapes have also been sold to specialty markets in Ontario. | Top of Page | References
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