Wild garlic

Images above: Upper left: Wild garlic plant (William Ferlatte). Upper right: Wild garlic plants (Randall Prostak, University of Massachusetts). Bottom left: Wild garlic hollow stem (Randall Prostak, University of Massachusetts). Bottom right: Wild garlic bulblets on ripe inflorescences (center) in a wheat field (Joseph DiTomaso, University of California, Davis).

Identification

Other common names:  field-garlic, wild onion, crow garlic, scallions, ramp

Family:  lily family, Liliaceae

Habit:  Perennial grass-like herb arising from a bulb.

Description:  Seedling leaves are slender, hollow, upright, hairless, round, and grass-like in appearance.  Seedlings smell of garlic or onion when crushed.  Mature plant leaves are similar to seedling leaves.  Leaves are 6-24” (15-61 cm) tall by 0.1-0.4” (0.3-1 cm) wide.  Below-ground bulbs are egg shaped, have papery coverings and can also develop in segments from the main bulb.  A fibrous root system emerges from bulb bases.  Stalks are unbranched, round, smooth, waxy, leafless, and solid-cored; the top of the stem gives rise to either aerial bulblets or flowers that emerge from a sheathed globular structure.  Aerial bulblets are small and teardrop shaped, with a thin, green leaf emerging from the top.  Maroon, pink, or white-green flowers may develop on the globe above the bulblets on 0.25-1” (0.6-2.5 cm) long stalks.  Occasionally, flowers produce three-chambered, egg-shaped capsules that contain up to 6 flat, wrinkled, black, 0.1” (0.25 cm) long seeds.

Summary of reproductive structures and terminology used:  Wild garlic reproduces primarily by production of four types of bulbs (Davis and Peters 1965, Lazenby 1961a, Ronsheim 1994).  Plants not sufficiently mature to produce a reproductive stalk form a terminal bulb in early summer that resumes growth in the fall.  Plants producing reproductive stalks usually form a single large soft offset bulb below ground in the axil of an inner leaf.  These generally sprout in the fall replacing the former terminal bulb.  Larger plants forming reproductive stalks typically produce one to four hard offset bulbs in the axils of outer leaves that can remain dormant for two or more seasons and produce new plants.  Aerial bulblets are small bulbs formed at the top of reproductive stalks.  Most plants emerge from bulbs and bulblets; seed production is rare in much of the U.S.A.  When flowers occur, they form in the same heads as bulblets and can produce seeds.

Similar species:  Domestic garlic (Allium sativum L.) plants generally have considerably larger stalks, bulbs and flowers than wild garlic.  Wild onion (Allium canadense L.) leaves are flat and solid when cut.  Wild onion bulbs do not become hard when dormant.  The white, star-shaped flowers and prominent, white mid-vein of star-of-Bethlehem (Ornithogalum umbellatum L.) distinguish it from wild garlic.  Star-of-Bethlehem also lacks the strong characteristic odor of wild garlic.

Management

Wild garlic is not a competitive weed and rarely causes noticeable yield loss, but has a large impact by tainting farm produce, thereby reducing its value (Lazenby 1961a).  When consumed by pastured livestock, it can produce a disagreeable taste in milk and meat.  In addition, the bulblets are harvested with cereal grains and are difficult to clean out of the grain.  Flour ground from contaminated grain has an unpleasant taste and odor.  Moreover, even a low percentage of bulblets in the grain (0.01%) can cause caking on the mill which necessitates frequent cleaning.  Consequently, mills reject contaminated grain shipments or levy heavy docking fees.  Wild garlic is less of a problem in vegetable crops, but separating the long thin leaves from salad and braising greens can substantially slow harvest and processing of these crops.

Wild garlic is best managed by late fall to early spring tillage.  The optimal time for tillage is when two foliage leaves are well formed (do not count the short sprout leaf, which quickly withers).  Tillage at this time destroys growing plants after reserves have been transferred to leaves but before new offsets and bulblets have formed.  Since development is not synchronized across all plants, several years of appropriately timed tillage will be needed to bring an infestation under control.  Repeated harrowing in fall and spring without primary tillage also greatly reduces the population, but generally is no better than fall plowing followed by spring harrowing and a spring planted crop.  Tillage in late spring will allow formation of offsets, but they will not have had time to form a hardened covering scale and, therefore, will not be dormant.  Mowing or tillage when the stalks have started to lengthen but are not full height will prevent or reduce production of bulblets (Lazenby 1963).  Plants will, however, still produce dormant offset bulbs at the base of the plant.  Summer fallow is useless for controlling wild garlic.  Plowing in the fall before plants have two long foliage leaves will kill a few plants by deep burial, but many will re-sprout and develop normally (Lazenby 1962b).  

Rotation of badly infested land to spring planted row crops is beneficial as it allows spring tillage and repeated cultivation to damage plants during the formation of offset bulbs and bulblet bearing stalks.  If the land is rotated to a summer planted crop, precede the crop with a spring fallow or with early plowing followed by a rapidly growing cover crop.  Spring sown cereal grains can also decrease wild garlic populations if tillage can be timed appropriately. 

Like its domesticated relatives, wild garlic is a poor competitor that will be suppressed by several years of competition from a dense stand of perennial grasses or legumes (Lazenby 1961a, 1962b).  Hence, in lightly infested pastures, use good management practices to insure a vigorous growth of grasses and legumes between grazing episodes.  This will also dilute the percentage of wild garlic in the forage and thereby reduce the risk of tainting milk and meat.  To reduce the potential for tainting of animal products, avoid early grazing of infested fields since wild garlic will present fodder to the animals before grasses and legumes begin growing.  Badly infested pastures should be tilled in late fall or early spring, and, if possible, rotated to crops in which wild garlic is more easily controlled for a few years.  If the land is easily eroded, plant to a perennial hay crop, and fertilize it well after establishment to ensure lush, vigorous growth.

Avoid planting winter grains on infested land.  If the infestation is sparse, an occasional winter grain crop may be grown successfully if the stand is good and the crop is vigorous.  Consequently, use a high seeding rate, and fertilize the crop well.  These measures should greatly reduce the number of bulblet bearing stalks and hence contamination in the harvested grain.  If the stand turns out poor, consider harvesting the crop for hay: the garlic flavor does not persist in dried hay as it does in fresh forage or silage.

Ecology

Origin and distribution:  Wild garlic is native to Europe and western Asia where it is widespread.  It occurs also in North Africa and has been introduced into North America, Australia, New Zealand and Chile.  In North America, the species is present throughout most of the eastern and central states, Ontario, and the moister parts of the far west, including British Columbia and Alaska (DeFelice 2003, USDA Plants).

Seed and bulblet weight:  Bulblets weigh from 3-70 mg and occasionally more, with the median around 17 mg (Håkansson 1963, Ronsheim 1994).  Larger bulblets have a higher germination rate than smaller bulblets (Krochmal 1960).  Seeds weigh 0.5-1.5 mg with a mean of 1.07 mg (Ronsheim 1994). 

Dormancy and germination:  All types of bulbs are dormant when produced, but terminal bulbs, soft offsets and most bulbils lose dormancy and begin sprouting by the summer or fall of the year they are produced (Stritzke and Peters 1970).  Bulblets lose dormancy after several months at 72 °F (22 °C), but not at 33-40 °F (0.6-4 °C) (Krochmal 1960), a pattern which favors plant establishment in early fall and a growth advantage when temperatures warm in early spring (Phillips 2010).  Sprouting of bulblets was higher at 68 °F (20 °C) than at 86 °F (30 °C) (Krochmal 1960).  The hard, waxy scale on hard offsets tightly surrounds the bulb and, despite completion of after-ripening, typically delays germination for a year or longer (Lazenby 1962a, Stritzke and Peters 1970).  Eventually, these coverings split or decay and the hard offset sprouts.  Sprouting of non-dormant hard offsets was best at 50 °F (10 °C) (Stritzke and Peters 1970).  Seeds require two to three months of cold, moist stratification to germinate (Ronsheim 1994).

Seed and bulb longevity:  Terminal bulbs and soft offset bulbs usually die if they do not sprout the autumn after production.  In one study, seeds and bulblets buried in the soil did not survive for a full year (Ronsheim 1994).  In other studies, however, 4-5% of bulblets survived more than one year, but not longer (Håkansson 1963, Krochmal 1960).  Hard offset bulbs can remain dormant in the soil for five years or more, though all but a few sprout within the first two to four years after production (Håkansson 1963, Lazenby 1962a, Stritzke and Peters 1970).

Season of emergence:  Bulbs sprout from August until the ground freezes.  Some shoots do not reach the soil surface until spring, however, so shoots emerge in both fall and early spring (Håkansson 1963).  Emergence in spring can also occur from bulbs at greater depth in the soil (Lazenby 1962a).  Seeds would be expected to germinate in spring based on their need for cold stratification (see Dormancy section), but this has never been observed in the field (Ronsheim 1994).

Emergence depth:  The ability of a bulb to produce a shoot depends on both depth and the size of the bulb.  Placement on the surface of soil reduced establishment and growth of plants compared to placement 0.5 to 0.75” (1-2 cm) deep (Lazenby 1961b).  Bulblets emerge best from the top 2” (5 cm) and generally cannot emerge from deeper than 4-6” (10-15 cm) (Lazenby 1962a).  Offset bulbs emerge best from the top 4” (10 cm) with minor emergence from 8” (20 cm) (Lazenby 1962a).  The largest bulbs can emerge from the bottom of the plow layer (8-10” = 20-26 cm) or deeper (16” = 40 cm) (Lazenby 1962a).  The likelihood of a shoot producing a reproductive stalk and the production of below-ground daughter bulbs declines with the depth of the parent bulb, particularly when the parent bulb is below 4-6” (10-15 cm) (Håkansson 1963).  Soft offset bulbs buried below this depth in fall or early spring produced few stems or inflorescence the following spring (Peters and Lowance 1981).  In long established grass swards, the largest bulbs and the most vigorous plants have their bases at about 2.75” (7 cm) below the soil surface.  This is apparently the optimum depth for terminal bulbs and hard offsets, and plants that first establish near the soil surface eventually pull themselves down to this depth by root contraction (Håkansson 1963).

Photosynthetic pathway:  C3

Sensitivity to frost:  Wild garlic is very resistant to even hard frosts (Håkansson 1963).  The leaves sometimes brown and die back to the soil surface, but continue to lengthen again in early spring along with additional new leaves (Håkansson 1963).

Drought tolerance:  Wild garlic is highly resistant to drought.  Plant growth slows during dry weather, but the bulbs will survive long drought periods, even when uprooted and lying on the soil surface following tillage (Lazenby 1962c).

Mycorrhiza:  Mycorrhiza have been noted (Harley and Harley 1987).  Mycorrhizal association with wild garlic is more important when nutrients are limiting (Ronsheim 1996).

Response to fertility:  Balanced fertilizer application appropriate for winter grain production moderately increases the likelihood of flowering, the number of foliage leaves per plant, the number of offset bulbs, and the average weight of the offset bulbs (Ronsheim and Bever 2000).  Plants arising from bulblets, however, had slower growth and produced fewer hard offsets when balanced fertilizer was applied, probably due to osmotic effects (Lazenby 1961a).  The strength of garlic flavor was reduced by sulfur deficiency in the nutrient medium (Freeman and Mossadeghi 1971).

Soil physical requirements:  Wild garlic grows successfully on a wide range of soil textures from heavy clay to coarse sand (Lazenby 1961a).  Bulbs can survive an entire growing season in waterlogged soil.

Response to shade:  Wild garlic tolerates moderate shade, but like its domestic relatives it is easily suppressed by competition from more robust plants.  In particular, competition from a vigorous crop greatly decreases formation of reproductive stalks, though in most cases the population will maintain itself by production of below-ground bulbs (Lazenby 1961a, 1962b).

Sensitivity to disturbance:  Wild garlic plants can be completely killed by burial at the two-leaf to early third-leaf stage (the little sprout leaf does not count in this regard) (Håkansson 1963).  Shallow burial before this stage will result in re-sprouting and normal growth.  Deep burial at greater than 4” (10 cm), however, will kill most younger plants.  Burial after the second to early third leaf stage may appear to have killed the plants, but they will form bulbs underground from energy reserves stored in the leaves (Lazenby 1962c).  Cutting the flowering stalk when it first forms prevents production of bulblets, but increases the size of offset bulbs by as much as three-fold.  Bulblets will continue to mature on a cut off or buried reproductive stalk once the stalk has reached its full length, even if the head has not begun to swell (Håkansson 1963).   Plants survive multiple defoliations by mowing or grazing (Lazenby 1963).  Plants cut in late spring or summer wait to re-sprout until the usual time in the fall (Håkansson 1963).  Dormant bulbs are essentially immune to management practices other than digging and removal.

Time from emergence to reproduction:  Shoots emerge throughout the fall, and reproductive stalks typically appear in mid spring (Håkansson 1963).  Plants require a cold treatment to induce stalk formation (Ceplitis 2001).  Stalks produce mature bulblets by late spring or early summer.  Plants establishing from bulblets generally require two to four seasons to mature (Håkansson 1963).

Pollination:  The occasional flowers that are produced are cross pollinated by bumble bees and flies (Ceplitis 2001, Ronsheim 1996).

Reproduction:  Wild garlic reproduces primarily by production of the various bulb structures described above, but occasional plants produce flowers and seeds as well (Lazenby 1961a, Ronsheim 1994).  Most reproduction occurs by formation of bulblets on the reproductive stalk where flowers would be expected on domesticated garlic.  Four populations in Sweden produced 75 to 141 bulblets per plant (Ceplitis and Bengtsson 2004).  Production of seeds varies greatly with season, locality and among plants, ranging from 3 to 70 seeds per inflorescence (Ceplitis 2001).  Seed production is rare in the northeastern U.S.A. (Uva et al. 1997).  Some genotypes of wild garlic tend to allocate more resources toward belowground asexual offsets and, occasionally, sexually-produced seeds, whereas other genotypes allocate more to aerially produced bulblets and less to offsets or seeds (Ronsheim and Bever 2000). 

Dispersal:  Bulblets and seeds disperse similarly short distances, with the majority found within 14” (35 cm) of the inflorescence (Rosheim 1994).  Bulblets move in contaminated seed grain, and especially rye and winter wheat used as cover crop seed since this is rarely certified for seed quality.  They are sometimes found in straw.  They also travel in mud on tires, farm implements, shoes and the feet of livestock.  Bulblets will float for many hours, and likely disperse with overland flow off of fields, along waterways and by blowing across ponds and lakes.  (DeFelice 2003).

Hard offsets disperse little distance from the parent plant, but can remain dormant several years.  In contrast, bulblets do not survive more than a year, but can disperse longer distances by the mechanisms discussed above, although most fall within a meter of the parent plant. (Ronsheim and Bever 2000).  Bulblet performance is maximum when dispersed 10” (25 cm) and declines with increasing dispersal distance from the parent plant, suggesting that local adaptation occurs at the scale of natural dispersal, thereby favoring asexual reproduction (Ronsheim 1997).  The evolutionary contribution of seeds to survival of the species has yet to be clarified (Ceplitis and Bengtsson 2004, Ronsheim and Bever 2000).

Common natural enemies:  Several fungi cause extensive damage to below-ground bulbs (DeFelice 2003).  These include onion white rot (Sclerotium cepivorum) and various species of Penecillium and Fusarium.  Slugs and rabbits feed on the foliage.

Palatability:  The bulbs are occasionally used to flavor cooked dishes, but most people consider the flavor much inferior to that of domestic garlic.  The bulbs do, however, contain substantial concentrations of the same beneficial anti-oxidants found in domestic garlic.  Livestock readily eat wild garlic leaves and shoots, but consumption of fresh material can taint milk and meat.  The flavor persists through the silage making process, but is not present in dried hay.  Consumption of large quantities of wild garlic can cause poisoning in both people and livestock.  (DeFelice 2003)

References:

• Ceplitis, A.  2001.  Genetic and environmental factors affecting reproductive variation in Allium vineale.  Journal of Evolutionary Biology 14:721-730. 
• Ceplitis, A., and B. O. Bengtsson.  2004.  Genetic variation, disequilibrium and natural selection on reproductive traits in Allium vineale.  Journal of Evolutionary Biology 17:302-311.
• Davis, F. S., and E. J. Peters.  1965.  Reproductive cycles of wild garlic and nomenclature of plant and bulb types.  Weeds 13:84-87.
• DeFelice, M. S.  2003.  Wild garlic, Allium vineale L. – little to crow about.  Weed Technology 17:890-895.
• Freeman, G. G., and N. Mossadeghi.  1971.  Influence of sulphate nutrition on the flavour components of garlic (Allium sativum) and wild onion (A. vineale).  Journal of Science of Food and Agriculture 22:330-334.
• Håkansson, S.  1963.  Allium vineale L. as a weed, with special reference to the conditions in south-eastern Sweden.  Växtodling (Plant Husbandry) 19:1-208.
• Harley, J. L., and E. L. Harley.  1987.  A check-list of mycorrhiza in the British flora.  New Phytologist 105:1-102.
• Krochmal, A.  1960.  Germination studies of aerial bulblets of Allium vineale L. and A. canadense L.  American Midland Naturalist 63:497-508.
• Lazenby, A.  1961a.  Studies on Allium vineale L.: I. The effects of soils, fertilizers and competition on establishment and growth of plants from aerial bulbils.  Journal of Ecology 49:519-541.
• Lazenby, A.  1961b.  Studies on Allium vineale L.: II. Establishment and growth in different intensities of competition.  Journal of Ecology 49:543-558.
• Lazenby, A.  1962a.  Studies on Allium vineale L. III. Effect of depth of planting.  Journal of Ecology 50:97-109.
• Lazenby, A.  1962b.  Studies on Allium vineale L. IV. Effect of cultivations.  Journal of Ecology 50:411-428.
• Lazenby, A.  1962c.  Studies on Allium vineale L. V. Effect of plant disturbance.  Journal of Ecology 50:429-438.
• Lazenby, A.  1963.  Studies on Allium vineale L.: VI. Effect of cutting.  Journal of Ecology 51:55-73.
• Peters, E. J., and S. A. Lowance.  1981.  Effects of date and depth of burial on wild garlic (Allium vineale) plants.  Weed Science 29:110-113.
• Phillips, N.  2010.  Seed and bulb dormancy characteristics in New World Allium L. (Amaryllidaceae): A review.  International Journal of Botany 6:228-234.
• Ronsheim, M. L.  1994.  Dispersal distances and predation rates of sexual and asexual propagules of Allium vineale L.  American Midland Naturalist 131:55-64.
• Ronsheim, M. L.  1996.  Evidence against a frequency-dependent advantage for sexual reproduction in Allium vineale L.  American Midland Naturalist 147:718-734.
• Ronsheim, M. L.  1997.  Distance-dependent performance of asexual progeny in Allium vineale (Liliaceae).  American Journal of Botany 84:1279-1284.
• Ronsheim, M. L., and J. D. Bever.  2000.  Genetic variation and evolutionary trade-offs for sexual and asexual reproductive modes in Allium vineale (Liliaceae).  American Journal of Botany 87:1769-1777.
• Stritzke, J. F., and E. J. Peters.  1970.  Dormancy and sprouting cycles of wild garlic.  Weed Science 18:112-114.
• USDA Plants.  USDA Natural Resources Conservation Service Plants Database.  http://plants.usda.gov
• Uva, R. H., J. C. Neal, and J. M. DiTomaso.  1997.  Weeds of the Northeast. Cornell University Press: Ithaca, NY.