Growing Garlic in Alberta
In Alberta, garlic, a cool-season crop, is planted in the fall and harvested the following summer. The following is information on the types of garlic grown in Alberta, garlic production from planting to storage, pest control and weed management.
Garlic (Allium sativum) belongs to the Alliaceae family, the same family as onions, shallots and leeks. The majority of Alberta-grown garlic is either produced for home use or sold to the fresh market as whole, fresh bulbs, green garlic or scapes.
There are two types of garlic grown in Alberta - hardneck and softneck. Hardneck varieties (allium sativum var. ophioscorodon) will bolt during early summer, producing a tall, flower stalk or scape. Bulbils, which are small aerial cloves, are produced at the tip of scapes (inside an umbel capsule) in place of a true flower.
There is a huge variation in the size and number of bulbils produced by hardneck garlic. They range from hundreds of small rice sized bulbils inside a single capsule, to a handful of large pea sized ones. Bulbils may be used as planting stock, but usually, require at least 2 years to develop into marketable bulbs. Often bulbils will form a single cloved bulb called a round, which can be replanted again to form a larger, multi-cloved bulb the next year.
Softneck varieties (A. sativum var. sativum) do not generally produce a scape, however, in cold climates like Alberta, some bulbs will sometimes form bulbils in the stem. A general rule of thumb is that hardneck varieties are more winter hardy, produce larger cloves but have a shorter storage life than softneck varieties. Traditionally, only hardnecks were planted in Alberta, however, there are now hardy softneck varieties that are suitable for the harsh winter conditions of the prairies (especially when covered by straw mulch)
Hardneck garlic can produce anywhere from 4-12 cloves per bulb. The main family groups grown in Alberta include Rocambole, Porcelain, Purple Stripe and Marble Purple Striped. Softneck garlic varieties produce an average of 8-12 cloves/bulb. The main softneck family group grown in Alberta is Artichoke.
Regardless of type, 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 or bulbils, with each clove or bulbil being a clone of the parent plant. Over many hundreds and even thousands of years, rare mutations have occurred, resulting in the different varieties we see today.
Garlic is a perennial plant that requires a cold period to initiate growth. In Alberta, garlic is grown as a winter annual, meaning that it is planted in the fall and then harvested during the following summer (preferably sometime between the end of September until the end of October). Although not ideal, it is possible to plant garlic in the spring. Planting stock should be placed in cold storage prior to planting to allow vernalization, which is required for proper bulb development.
It is critical that garlic not be planted too early or too late in the fall. Planting depth is also important. If planted too early or not deep enough, there is a risk that leaves will emerge from the soil and be prone to winter injury. If planted too late, there is a risk that cloves will not develop adequate root systems or be winter hardy. A strong, well-established overwintering plant will quickly develop shoots in spring as the soil and air temperatures increase. With adequate moisture and fertility, a large plant will develop before bulbing takes place.
It is ideal to have the cloves planted with the pointed side up, as they will grow nice straight necks. Cloves planted on their sides or upside down will often have a curved shoot and sometimes misshapen bulbs, although they will still develop a good size.
It is important to store healthy seed stock as whole bulbs until just before planting (preferably less than 24 hrs) since cloves separated from the parent bulb deteriorate more rapidly than whole bulbs. Dry bulbs are more easily broken apart into cloves than damp bulbs. Garlic can be cracked by hand or mechanical devices. However, there is greater potential for physical damage to cloves when mechanically cracked. Some mechanical planting equipment requires that cloves be graded into sizes or weight ranges for improved planting efficiency.
Cloves can be planted 1" to 3" deep, anywhere from 4" to 6" apart in row and 8" to 12" between rows. The spacing between rows usually depends on the method of planting and preferred methods for weeding (use of equipment or by hand). Single rows with wide spacing or multiple rows of plants with tighter spacing (often on raised beds) are both commonly used.
Some Alberta growers use bulbils as their planting stock. The main advantage of planting bulbils is that it allows growers to increase their planting stock very quickly and it is thought to produce seed stock free of some soil-borne diseases (although some growers are sceptical of this due to lack of research on this theory). The disadvantage is that it can take several years of successive plantings to achieve good-sized bulbs from the initial bulbil planting stock.
Just as with garlic cloves, bulbil capsules should be broken open and individual bulbils removed for planting just prior to planting. Planting densities for bulbils will depend on the size of the bulbils and the preference of the grower.
Planting bulbils closer together allows for easier management, but care must be taken to provide adequate space for bulb growth. Growers that use bulbils as seed must ensure that their plantings are watered regularly due to their shallow root systems.
Planting Location and Soil Preparation
Garlic can be grown successfully in a wide range of soil types and is grown in most cultivated areas of Alberta.
Soils with high organic matter content are preferred, due to their increased moisture and nutrient holding capacity. Soils containing high levels of organic matter tend to be less prone to crusting and compaction. Heavy clay soils can be challenging during wet periods (allow conditions can be improved greatly with the use of raised beds). Consistent irrigation and water conservation practices are required on light sandy soils due to their low moisture holding capacity.
Garlic grows well on fertile soils, however, fertilizer recommendations for garlic in Alberta are not been fully determined. Verify the soil phosphorus and potassium levels with a soil test. Broadcast any required phosphorus or potassium followed by shallow incorporation into the soil before fall planting. The amount of nitrogen required will vary with soil type, the previous crop grown, the amount of organic matter present and the climatic conditions during the growing season. Depending on soil type and organic matter content, it is generally accepted that garlic requires 100-150 lbs N/acre, 150 lbs P/acre, and 200-400 lbs K/acre. With a small amount applied in the fall, apply half the nitrogen as soon as the garlic begins to grow in early spring and the remainder split into two to three applications at 3-week intervals. Complete the last application of nitrogen 4 to 6 weeks prior to harvest.
Choose fields where good snow cover occurs to enhance plant survival. Choose fields that provide ample wind protection when possible, especially where garlic is planted on lighter soils.
In much of Alberta and Western Canada, many growers mulch for the winter. Mulching helps moderate soil temperatures and protects the cloves from the harsh winter conditions of the prairies. This is especially important in Alberta where drastic warm weather can occur during the winter resulting in all the protective snow cover melting before spring.
While several different mulches are commercially available, it is important to ensure you don't mulch with materials that could be contaminated with garlic pests, such as bulb and stem nematode, bulb mites, diseases or weed seed. The most commonly used mulch is straw, applied 4 to 6 inches deep directly over the planted garlic rows.
In the spring, most growers remove the mulch completely once the threat of frost is over, while others leave it on throughout the season to help maintain moisture and provide weed control.
Garlic is sensitive to moisture stress throughout the growing season. Periods of dry soil conditions, especially during bulb formation, will result in reduced yields.
For most soils, approximately 1 inch of water per week is required during the growing season. In sandy soils, however, 2 inches or more of water is usually required during hot and dry conditions.
Preferably, garlic should be irrigated in the morning to mid-afternoon. This allows sufficient time for the plants to dry before evening. Irrigation should be stopped around two weeks before harvesting. This will make the harvesting process easier and help reduce potential deterioration or staining of the bulbs.
In hardneck varieties, research has shown that when the scape is left on the plant, bulb yields can be decreased by as much as 30%. This is because energy is diverted to bulbil production rather than bulb growth. Remove scapes snapping, pulling or cutting just after they have begun to curl, but before they straighten out.
Bulbs continue to size 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. Begin harvesting when 30%-50% of the leaves have died back. Ensure that there are at least 5 healthy green leaves remaining at harvest. Garlic bulbs harvested too early may be immature and tend to shrivel when cured, while late harvested bulbs may have stained, partially decayed wrapper leaves and/or 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 usually mechanically harvested using a tractor-drawn undercutter blade that loosens the soil beneath the bulbs. A mechanized system can be used to lift the bulbs, remove the tops and separate the dirt and trash for growers that are large enough.
Garlic needs to be cured once harvested. Curing is the process of drying the bulbs to help increase storage life by minimizing microbial and fungal infection and water loss. Harvested garlic should be left in the field to cure for a couple of days or be removed from the field immediately and cured in storage. To cure garlic in the field, place plants in covered, slotted vegetable bins and allow natural air drying. To cure in storage, tie 10-15 plants into a bundle and hang to dry in a well-ventilated area or use forced air to dry the bulbs. 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 (table stock) can be stored differently than garlic for planting stock. Garlic for table stock is best stored at 0°C-4°C with a relative humidity of 60%-70%. Avoid storing in higher humidity, as it creates an excellent environment for penicillium mould and root growth. Table stock stored at room temperature may dehydrate faster. Store garlic intended for planting stock at anywhere from 10°C to room temperature with 60%-70% relative humidity.
At room temperature, hardneck varieties can be stored up to 4 months; softneck varieties up to 8 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.
Pest Control and Weed Management
Insects and Diseases
There are a number of pests of garlic in Alberta, including fusarium basal plate rot, penicillium mould, bulb and stem nematode, and viruses.
Fusarium Basal Plate Rot
Fusarium basal plate rot attacks the basal plate region of the bulb and roots. This soil-borne pathogen invades the roots, resulting in empty, tan-colored, 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.
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. 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 4-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.
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 a 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 properly disposing of cull garlic is necessary for 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. Always remove plants that look diseased or sick from the field during the growing season.
Garlic is a weak competitor against vigorous weeds. Weed management is essential and can be undertaken by cultivation, hand hoeing, mulching or with herbicide applications. Avoid deep cultivation close to the plants, as root damage and subsequent yield losses, may occur.