Growing Garlic in Manitoba
In Manitoba, garlic is considered a cool-season crop that is usually planted in the fall and harvested the next summer. The following is information on the types of garlic grown in Manitoba, garlic production from planting to storage, and pest control and weed management.
Garlic (Allium sativum) is from the same family (Alliaceae) as onions, shallots and leeks. The majority of Manitoba grown garlic is grown by home gardeners or small farms that sell fresh bulbs and scapes through local stores or at Farmers' Markets.
There are two types of garlic grown in Manitoba - softneck and hardneck. Hardneck varieties bolt in late spring or early summer. This produces a tall flowering stalk call a scape (Figure 1). At the tip of the scape, a capsule forms containing bulbils. These are very small cloves that can be used as planting stock, but usually require 2 or more seasons to develop into good sized bulbs. Bulbils usually produce rounds (single cloved bulbs) in their first year. There is a huge variation in the size and number of bulbils produced by hardneck garlic. Larger bulbils tend to produce lager bulbs more quickly.
Softneck varieties on the other hand, do not produce scapes. Generally, hardnecks are considered more hardy and suitable for cold climates. Also, hardnecks tend to have larger cloves, but have shorter storage life than softnecks. In Manitoba, softnecks can be grown successfully, however, growing them in a sheltered location and good winter protection will recommended.
Hardneck garlic can produce anywhere from 4-12 cloves per bulb. Varieties grown in Manitoba include Porcelain, Rocambole, Purple Stripe, Marbled Purple Stripe and Artichoke. Softneck varieties grown in Manitoba include Silverskin and Artichoke. These softenck families produces an average of 8-12 cloves per bulb in Manitoba's climate.
Figure 1. Hardneck garlic variety with scapes.
It is important to note that cultivated garlic plants are not able to produce true seed, therefore, genetic material is not exchanged between different varieties. All garlic is propagated vegetatively from cloves or bulbils, meaning that each clove or bulbil being planted is a clone of the original parent plant.
Garlic is a perennial crop that needs a cold period in order to form bulbs and grow properly. In Manitoba, garlic is generally planted in the fall and harvested the following summer. Although fall planting is the best option, it is also possible to plant in the spring (see Growing Garlic in Spring for more info).
It is important to try and plant garlic at the proper time in the fall. Planting too early can cause the plants to grow quickly and emerge from the ground before winter arrives. If this growth is substantial, it can leave the young plants susceptible to winter kill. Planting too late does not allow the garlic cloves enough time to get their roots established and settled into dormancy for the winter.
Planting depth is also important. If the cloves are placed too deep, wet soils can cause them to rot and cloves will be forced to use excess energy from the soil. A depth of 1 to 2 inches in heavy soils (clay) and 2 to 3 inches in light soils (sand) is a good benchmark. If trying to grow perfectly symmetrical bulbs, it is a good idea to try and plant cloves with the pointed side up. Although most cloves planted on their side will also develop nice looking bulbs, they may be slightly misshapen.
In spring, well-established plants that were planted at the right time and depth will rapidly emerge from the ground as soil and air temperatures increase. With adequate moisture and nutrition, a large plant will develop before the bulbing process begins.
Only good quality bulbs should be used for seed stock. The garlic should be stored as whole bulbs until just before planting. Cloves that have been cracked and separated tend to deteriorate fairly quickly. Dry bulbs are more easily broken apart into cloves than damp bulbs. Garlic can be cracked by hand or with specialized equipment although mechanical cracking tends to cause physical damage to some of the cloves.
The amount of planting material required will vary from 100 to 200 bulbs/1,000 ft2 (5,000 to 10,000 bulbs/acre) depending on the number of cloves per bulb. Cloves should be planted 4 to 6 inches apart in the row and 8 to 12 inches between rows. Spacing between rows depends on the method of planting and the equipment available for cultivation. Generally, the more space given, the larger the bulbs will grow.
Some Manitoba growers use bulbils as planting stock, although this is not widely practiced. Depending on the variety, capsules can contain from four to a few hundred bulbils (Figures 2 and 3).
Figure 2. Porcelain bulbil capsules.
Figure 3. Asiatic garlic bulbil capsules.
The main advantage of planting bulbils is that it allows growers to increase their planting stock very quickly and to minimize transmission of some soil-borne diseases. The disadvantage is that it can take many years of successive plantings to before attaining good-sized bulbs from the initial bulbil planting stock.
Similar to garlic, bulbil capsules should be broken open and individual bulbils removed just before planting. Bulbils can be planted from a few inches to several inches apart. Adequate moisture through rain or irrigation is critical for bulbils to develop properly due to their small and shallow root systems.
Planting Location and Soil Preparation
Garlic can be grown in all regions of Manitoba where other cold hardy vegetables can be grown and is tolerant of a wide range of soils
Soils with high organic matter content are ideal because of their high moisture and nutrient holding capacity. These soils are also less prone to crusting and compaction which allows for easy formations of bulbs. Heavy soil such as clay can hinder bulb expansion, especially if allowed to dry out. That being said, there large numbers of growers with clay soil that have great success and produce large beautiful bulbs every year. On light sandy soils, good soil management practices are needed due to their low moisture-holding capacity and low fertility.
Garlic grows well on fertile soils and it is important that adequate fertility is added to the soil if large bulbs are desired. Any organic additions (such as manure or compost) should be thoroughly incorporated well in advance of planting to allow the nutrients to be available to the plants. Any phosphorus or potassium fertilizers should also be incorporated prior to planting. A small portion of the Nitrogen required can be added in fall, however, the remainder should be applied in spring and split into 2 or 3 applications. The last application of Nitrogen should be completed within 4 to 6 weeks of harvest.
The amount of fertility required will vary with soil type, the previous crop grown, the amount of organic matter present and the climatic conditions during the growing season. That being said, a good fertility target for most growers is the following:
Nitrogen: 120 lbs/acre
Phosphorus: 150 lbs/acre
Potassium: 160 lbs/acre
Sulfur: 30 lbs/acre
It is a good practice to plant garlic in an area where there good winter snow cover. In Manitoba, most growers mulch their plantings for the winter. Mulching helps moderate soil temperatures and protects roots and shoots from fluctuating temperatures. It is important to ensure you don't mulch with materials that could have weed seeds and other pests. The most commonly used mulch is straw, applied 10-15 cm deep directly over the planted garlic rows (Figure 4).
Figure 4. Garlic rows covered in straw mulch.
In the spring, the mulch can be completely removed once the threat of frost is over, or left on throughout the season to help maintain moisture and provide weed control. Leaving the mulch on for the entire growing season can make weeding difficult and can contribute to disease problems, especially on heavy soils and during heavy rains.
Garlic is very sensitive to moisture stress throughout the growing season. Dry soil conditions, especially during the bulbing phase, can result in significant yield reductions.
For most soils, approximately 1 inch of water per week is required during the growing season. In sandy soils, 2 inches or more of moisture may be required especially during hot and dry weather conditions.
The best time for irrigating is from the morning to mid-afternoon. This allows sufficient time for the plant foliage to dry before the evening. Irrigation can be stopped about two weeks before the bulbs are ready to be harvested. This will make harvesting easier and help minimize any quality issues such as stained bulb skins.
Hardneck varieties produce a scape that should be removed for maximum bulb size. Research has shown that when the scape is left on the plant, bulb yields can be reduced by as much as 30% because energy is diverted to bulbils rather than filling out the bulb. Remove scapes by breaking or cutting just after curling but before they straighten out (Figure 5).
Figure 5. Scape ready for removal.
Bulbs continue to increase in size during late spring and summer until the leaves of the plant begin to dry and turn brown. Leaf browning progresses from the tips towards the base leaves and starts with the lower leaves. Harvest should begin when approximately 30%-50% of the leaves have turned brown and died back. Garlic bulbs harvested too early may be immature, undersized and tend to shrivel when cured. Late harvested bulbs may be stained, have partially decayed leaf wrappers and exposed cloves.
Small plantings of garlic are often hand harvested with the aid of a fork to loosen the soil and help with lifting. Larger plantings are normally harvested using a tractor-drawn under-cutter blade that loosens the soil just below the bulbs.
Once the garlic is harvested, it must be cured. Curing is the process of drying the bulb to help increase storage life by minimizing microbial and fungal infection and water loss. Harvested garlic can be left in the garden or field to cure for a few days or be removed from the field immediately and fully cured in storage.
To start the drying process in the field, lay garlic on the ground in rows, covering the bulbs with the tops of the previous row of garlic.This will keep the bulbs out of direct sunlight and prevent damage. The garlic can be left outside for 3 to 7 days and should be removed early if very wet weather is forecast.
Once brought inside, tie the garlic into 10-15 plant bundles and hang to dry in a well-ventilated area that has natural air flow or forced air. Once cured, trim or remove garlic tops and roots and place the bulbs in slotted bins, on wired racks, or on open trays in a well-ventilated building.
Similar to bulbs, bulbils must be cured prior to storage. Harvest scapes with the bulbil capsule intact just prior to garlic bulb harvest. Once harvested, bunch, tie and hang scapes to dry for a few weeks. Once dried, remove the bulbil capsules and store them in a dry location until the time of planting.
Storage conditions depend on the end use. Garlic for consumption (food) can be stored differently than garlic that will be used for planting stock.
Food garlic can be stored at 0°C-4°C with a relative humidity of 60%-70%, although this is best suited for commercial farms who have the proper storage equipment. Most homeowners or market gardeners can store their garlic at room temperature or slightly cooler in an area with good ventilated. Humidity should stay below 70% to avoid moulds and root growth.Table stock stored at room temperature may dehydrate faster.
Garlic intended to be used as seed should be stored from 10°C to 20°C room temperature with 60%-70% relative humidity.
At room temperature, hardneck varieties can be stored 4-6 months and softneck varieties up to 8-12 months months. In temperature and humidity controlled conditions, storage life can be increased to 6-7 months for Rocamboles, 8-10 months for Porcelains and over 12 months for softneck types.
Garlic is a very weak competitor against weeds and requires planning. All perennial weeds should be eliminated prior to planting. Control of annual weeds must be early and continuous throughout the growing season. Weeding can be done through cultivation, hand hoeing, mulching or with herbicide applications. Avoid deep cultivation close to the plants, as root damage and subsequent yield losses may occur.
Insects and Diseases
There are a number of pests of garlic that all Manitoba growers should be aware of. These include Fusarium basal plate rot, Penicillium mould, bulb and stem nematode, white mould and viruses.
Fusarium Basal Plate Rot
Fusarium basal plate rot attacks the basal plate region of the bulb and roots (Figure 6). This soil-borne pathogen invades the roots, resulting in empty, tan-coloured, non-functional roots, while the basal plate region may develop a pinkish-brown growth of mycelium. Above-ground symptoms include yellowing of the leaf tips and dieback of the shoot during the spring. Warm soil temperatures and high soil moisture promote disease development. Since the organism survives as dormant spores in the soil or on plant residue, rotate with non-allium crops.
Figure 6. Fusarium basal plate rot of garlic bulb.
Penicillium mould is the main cause of decay of garlic in storage. The disease appears as masses of blue-green growth 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, healthy cloves may be contaminated with airborne spores. Wounded cloves are particularly susceptible to this disease.
Infected cloves are often invaded by secondary decay 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. Warm temperatures (22°C-25°C) are optimal 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.
Bulb and Stem Nematode
Bulb and stem nematode is a microscopic parasitic nematode that enters garlic through the roots or wounds on bulbs. Early in the season, young seedlings infected with nematodes are often stunted, with yellowing and bloating of young leaves. Later infections can cause twisting of new growth, bulb softening and desiccation, and loss of roots (Figures 8 and 9). Bulb and stem nematode becomes active in the spring with damage symptoms generally appearing mid-July through harvest. The key to management of this pest is prevention. This means planting nematode-free seed into nematode-free soil. Test your soil before planting, use clean seed and follow a 3-year rotation with non-host crops. Once in the soil, bulb and stem nematode can be spread through irrigation water, on contaminated seed, equipment, humans and animals.
Figure 8. Underdeveloped garlic bulb; absence of roots on one side of basal plate is an indicator of stem and bulb nematode infection.
Figure 9. Rotting of basal plate due to stem and bulb nematode infection.
White rot is a soil-borne fungal disease that can survive as sclerotia in infected fields for decades. It is a serious concern, particularly in cool, wet growing seasons. Symptoms of white rot of garlic include yellowing, wilting and toppling over of older leaves, watery bulbs and the presence of a fluffy, white mycelium and pinhead-sized black sclerotia, as well as rotted roots. Because sclerotia and mycelium overwinter in soil and plant debris, thorough cleaning of field equipment and proper disposal of cull garlic are important in preventing the spread of white rot to uncontaminated fields.
Virtually all sources of garlic contain viruses, though most are latent (dormant). Latent garlic viruses may not become visible or reduce yields until the garlic plant is stressed or growth is 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.