Growing Garlic in British Columbia
In British Columbia, garlic is generally planted in the fall and harvested the next summer. The following is information on the types of garlic grown in British Columbia, how the crop is produced from planting to storage, pest control and weed management.
Garlic (Allium sativum) is in the Alliaceae family, along with its cousins the onion, shallot and leek. The majority of the garlic grown in British Columbia is either produced for home use or sold fresh to customers as whole bulbs, green garlic, scapes or garlic powder.
Types & Family Groups
There are two types of garlic grown in B.C. - 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 the colder parts of B.C. (especially the North), 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, hardnecks were the main choice of growers in B.C., however, there are now hardy softneck varieties that are suitable for most regions of Canada (especially when covered by straw mulch). Softnecks can do especially well in the coastal areas of B.C. where the winters are mild and spring comes early.
Hardneck garlic can produce anywhere from 4-12 cloves per bulb. The main family groups grown in B.C. 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 B.C. 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 B.C., garlic is usually considered a winter annual, meaning that it is planted in the fall and then harvested during the following summer. For colder regions of B.C., planting is usually done sometime between the end of September until the end of October. For the milder coastal areas such as Vancouver and Victoria, planting is usually done between the middle of October and the middle of November.
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.
Although not ideal, it is also possible to plant garlic in the spring. Planting stock should be placed in cold storage for a few weeks prior to planting to allow vernalization, which is required for proper bulb development. Spring planting should be done as early as possible to allow the maximum amount of top growth to occur before bulb formation. This usually means planting as soon as the soil can be worked.
Cloves should be planted with the pointed side up when possible, 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. This is not a problem for home use, however, when selling nice well formed bulbs are preferred by customers.
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 tend to deteriorate fairly quickly. 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.
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 B.C. 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. 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 & Soil Preparation
Garlic can be grown successfully in a wide range of soil types and is found being cultivated in most areas of B.C.
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 (although 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 and generally appreciates additions of fertilizer or organic amendments that increase fertility. It is recommended that a soil test be taken to determine the nitrogen, phosphorus and potassium levels of the soil.
Broadcast any required phosphorus or potassium followed by shallow incorporation into the soil before fall planting. General recommendations for garlic are for 150 lbs P/acre and 200-400 lbs K/acre.
Although dependent on soil type and organic matter content, it is generally accepted that garlic requires at least 100-150 lbs N/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.
For colder locations in B.C. choose fields where good snow cover occurs to enhance plant survival. Choose fields or garden areas that provide ample wind protection when possible.
In much of B.C. and the rest of Canada, many growers mulch for the winter. Mulching helps moderate soil temperatures and protects the cloves from any harsh winter conditions that arrive. This can be especially important in B.C. where drastic warm weather can occur during the winter resulting in all the protective snow cover melting before spring. The most commonly used mulch is straw, applied 4 to 6 inches deep directly over the planted garlic rows.
In the spring, some 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. On heavy soils, leaving the mulch on can cause excess moisture issues, sometimes leading to disease.
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 reduced by as much as 30%. This is because energy is diverted to bulbil production rather than bulb growth. Remove scapes by 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 two to seven 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 for garlic 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 this creates an excellent environment for penicillium mould and root growth. Table stock can also be stored at room temperature in a cool well ventilated area, but may dehydrate faster. Store garlic intended for planting stock at anywhere from 10°C to room temperature with 60%-70% relative humidity. Plant as soon as possible to prevent deterioration of the bulbs.
At room temperature, hardneck varieties can usually be stored up to 5 months and softneck varieties up to 10 months. In temperature and humidity controlled conditions, storage life can be increased to 8 months for hardnecks and over 12 months for softneck types.
Pest Control and Weed Management
Insects and Diseases
There are a number of pests of garlic in B.C., including fusarium basal plate rot, penicillium mould, bulb and stem nematode, white rot 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 most 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. Garlic weeding is best done by early and frequent hoeing, cultivation or tillage.