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Find production information on one of Illinois' most profitable and delicious crops.
Extension Educator, Local Food Systems and Small Farms
University of Illinois Extension
402 Ava Rd.
Murphysboro, IL 62966
Onions and Garlic
Garlic (Allium sativum) is an excellent crop to promote as a local specialty, since locally grown garlic is a popular produce item at farmer’s markets and other similar markets in the lower Midwest. Garlic is one the most widely used culinary herbs and has recently gained additional attention as a potent medicinal herb. Garlic is a popular vegetable/herb since consumers are familiar with its use as an ingredient in various culinary dishes.
Garlic is one of the easiest vegetables to grow in the Midwest due to the lack of significant disease and insect pest problems. Garlic is highly adaptable to sustainable production or organic systems due to the low inputs required, as adequate crops can be produced with little added fertilizers or pesticides. The crop has great potential for local market sales as growers can obtain a reasonable return on small investments, since few off-farm inputs are required to produce the crop. There is great potential to add this easily grown, highly sustainable crop to local direct marketing systems.
Garlic is well adapted for production in the lower Midwest. Allium sativum can be divided into two subspecies: ophioscorodon (hardneck garlic) and sativum (softneck garlic). Hardneck types generally perform better in colder climates, and the cloves are typically larger and easier to peel. Hardnecks produce only a few large, uniformly-sized cloves per bulb, and the cloves encircle the central stalk only once. Softnecks have 3 to 6 clove layers that encircle the stem, with about 12 to 25 cloves per bulb; the outer cloves are large while inner cloves are small and thin.
There are distinct types within each garlic subspecies. Hardneck types include rocambole, purple stripe and porcelain. Rocamboles have parchment skins that are much thinner than softnecks; although the thin skins make peeling easier, they don’t store well. Rocambole garlic usually has up to a dozen cloves of a tan or brownish color. Purple striped garlic is highly distinctive because of its bright purple coloring or markings. Porcelain garlic has only a few very large cloves (with as few as four) per bulb. ‘Spanish Roja’, ‘Carpathian’, ‘Music’ and ‘Persian Star’ are hardneck cultivars suited to the lower Midwest environment.
Softnecks includes both silverskin and artichoke types. The silverskin is the type of garlic most often found on supermarket shelves due to their long storage life, and can be stored for about eight months without significant amounts of decay. They are the most popular garlic for braiding since they have sturdy necks. Silverskins have smooth, silvery, and shiny white skins with cloves that tend to be symmetrical in shape. The bulbs are composed of many small cloves. Although softneck garlic types like ‘Idaho Silverskin’ will produce under the lower Midwest climate, they are not as cold hardy and may be damaged by excessively cold winters. The artichoke type has several overlapping layers of cloves that tend to be very difficult to peel. Bulbs usually contain about 3 to 5 clove layers containing 12 to 20 total cloves. Outer cloves are fat and rounded but irregularly shaped, while inner cloves are much smaller.
Garlic is typically propagated by planting bulblets (or cloves). The size of the clove is an important consideration when selecting planting stock. The bulb must be broken into individual cloves. Garlic cloves should be graded for both size and quality prior to planting, with diseased, small, soft, damaged, or discolored cloves discarded. The cloves should be planted with the basal plate-side down. Under lower Midwest conditions, the cloves should be planted about 1-2 inches deep; and where winters are more severe, they should be planted about 2-4 inches deep.
Fall planting is recommended for garlic, as garlic must go through a cold period to produce the highest yields as well as for the development of cloves on the bulb. October is a good month to plant garlic, as it will allow sufficient time for some root and foliage development before the ground freezes. Garlic should be planted in the fall about 6 to 8 weeks before the ground freezes. Fall-planted garlic will grow quickly once the weather warms in spring.
Garlic is often planted in 6 to 8 inch high raised beds to provide easier digging of bulbs and better soil drainage. Individual rows need to be 12 to 36 inches apart (depending on whether a raised bed is utilized), with garlic plants spaced about 12 inches apart in-the-row. Mulching of garlic with an organic material such as wheat straw soon after planting will help improve winter survival, conserve soil moisture, suppress weeds, and prevent soil erosion. Garlic should emerge through an inch or more of mulch with no problem. However, try to avoid planting garlic in areas that have poor water drainage.
Garlic will grow in almost any well-drained, friable soil and a pH of 6.8 to 7.2 is optimal. Garlic is a heavy feeder and about 100 lbs N, 200 lbs P2O5 and 200 lbs K2O per acre is needed. Broadcast and incorporate about 25 lbs N and 50 lbs of each P2O5 and K2O per acre before planting in the fall. Apply about 40 lbs N and 100 lbs of each P2O5 and K2O per acre when garlic begins to grow in the spring (March), and split the remaining amounts of N, P2O5 and K2O at two sidedressings about 3 and 6 weeks after the early spring application. Avoid N applications when the bulbs begin to enlarge, since it will encourage excessive leaf growth at the expense of bulb size, and also within 2-3 weeks of harvest.
Scape Development and Removal
Garlic will often put up a tall, woody flowering stalk (or scape) that grows bulbils at the top. Hardneck garlic types will produce a scape, whereas softneck types do not. Flowers on these scapes generally abort and form bulbils, which are small, aerial cloves that can be used for propagation. However, if planted, bulbils will take up to two seasons to produce mature bulbs. If a garlic plant is allowed to put energy into these bulbils, the bulb forming below the ground will be about one-third smaller than if the scape is removed. It is best to cut scapes and remove when they are first developing on the plant.
One inch of water per week, via natural rainfall or supplemental irrigation is needed for optimal garlic growth. Drip or trickle irrigation is recommended as the supplemental water source. Garlic has a relatively shallow root system and is sensitive to dry soil conditions. The most critical stage for irrigation needs is during bulbing (mid-May to late June in the lower Midwest). Insufficient irrigation or rainfall during this stage will result in smaller bulbs. However, irrigation should be stopped about two weeks before harvest to prevent bulb diseases and discolored bulb wrappers.
Although, insects and diseases cause minimal problems on garlic grown in the lower Midwest, weed control is essential to achieving productive garlic yields. However, there are many insect pests that will attack garlic, such as thrips and onion maggots. Onion thrips are probably the most common insect pest that attacks garlic. The nymphs and adults scrape the outer surface of the leaf, and when damage is severe, the entire plant may wilt and die. Onion thrips often migrate to garlic from weeds surrounding fields. Since adults and nymphs inhabit weedy areas surrounding fields, these areas should be kept weed-free to reduce thrips infestations. After the crop is harvested, the tops should be piled together in some manner and burned to reduce over-wintering populations.
Certain types of diseases, such as Alternaria Purple Blotch, Botrytis leaf blight, and Downy mildew, can devastate garlic under specific environmental conditions. Cultural practices, such as planting certified disease-free cloves, using crop rotations away from other Allium spp. and proper field sanitation methods (e.g., removal of diseased foliage from the field after harvest) will reduce disease problems.
Garlic is a poor competitor with weeds, and unless weeds are controlled early, they will overtake young garlic plants and cause significant yield and quality loss. Since garlic is planted in the fall and harvested about 8 to 9 months later, various winter and summer annual weeds compete with garlic over this period of time. Mulching of new plantings has already been briefly mentioned as a way to control weeds, and the use of straw mulch will greatly reduce weed pressure. The mulch is often removed in the spring to allow the soil to warm up and then placed back around plants several weeks later. A few soil-applied and post-emergence herbicides are registered for use on garlic to control both grasses and broadleaves.
Harvest and Storage
Determining the proper time to harvest is very important, as over-mature garlic cloves will begin to crack apart while still in the ground. When the leaves start turning brown in late June, gently dig or pull up bulbs. When the bulbs are fully developed, the outer skin should be tight around the cloves. However, about two weeks prior to garlic harvest, do not irrigate and allow the soil to dry out around plants. In smaller plantings, garlic can easily be dug with a garden or potato fork. However, bed lifters, potato diggers, subsoilers, and other purchased or homemade extraction devices can be used to harvest garlic from larger acreages. Damaged or diseased garlic should be immediately discarded. Harvested plants and bulbs should be placed in a cool, dry location that has good air circulation to dry for about 2-3 weeks. Once plants have dried, most dead foliage can be clipped off with the stem, only leaving about ¼ to ½ inch of the stem with the bulb. At this time, the soil should be shaken from plants, cleaned to remove excess scales and placed in a cool location. Garlic should keep for 6 to 7 months if it is stored at 32° F and at 65 to 70 percent relative humidity. Garlic for long-term storage or for next year’s planting stock should not be washed.
Support provided by the College of Agricultural Sciences, the Department of Plant, Soil and Agricultural Systems, and the Illinois Council on Food and Agricultural Research (C-FAR).
Published June 2007