Wild onions and wild garlic are persistent perennial weeds that quickly frustrate homeowners. These members of the Allium genus infest lawns and gardens, often becoming noticeable in cooler months when turfgrass is dormant. Their distinctive, pungent odor when crushed or mowed signals their presence, and their rapid spread makes eradication challenging. Their unique biology allows them to survive common weed control methods.
Understanding Wild Onion and Wild Garlic
Both wild onion (Allium canadense) and wild garlic (Allium vineale) are difficult to control because they reproduce primarily through underground bulbs, not just seeds. If the green foliage is removed, the stored energy in the bulb allows the plant to regenerate quickly. Wild garlic is the more common and aggressive species, forming several small, hard offsets, or bulbils, around the main bulb.
A key to identification lies in the leaves, which affects herbicide effectiveness. Wild garlic leaves are round and hollow, while wild onion leaves are flat and solid. Both species have a thin, waxy coating, or cuticle, which serves as a protective barrier. This waxy layer significantly impedes chemical control by preventing herbicides from easily penetrating the plant tissue.
Manual and Cultural Control Methods
For small, isolated infestations, physical removal is a direct and effective option, provided it is done meticulously. Simply pulling the visible stalk is ineffective because the foliage breaks away easily, leaving the regenerative bulb intact deep in the soil. This often triggers the underground bulb to produce new shoots, multiplying the problem.
The correct approach involves using a trowel or thin shovel to dig out the entire clump, ensuring the removal of the primary bulb and all attached offsets. Attempt this when the soil is moist to minimize the chance of bulbils separating and remaining in the ground. Once removed, the plant material should be discarded, not composted, to prevent the bulblets from reestablishing themselves.
Mowing does not kill the plants but serves as a cultural control to reduce their vigor. Regular mowing prevents the formation of aerial bulblets, which are small structures produced at the top of the stem, especially on wild garlic. For small, concentrated areas, covering the infestation with a thick layer of mulch or solarizing the soil with clear plastic can suppress the plants by blocking sunlight and increasing soil temperature.
Strategic Herbicide Application
Chemical control is the most practical solution for widespread infestations, but it requires a strategic, multi-season approach due to the plant’s waxy leaves and bulb structure. Systemic, post-emergent herbicides are necessary because they are absorbed by the leaves and translocated down to the bulb to kill the entire plant. Products containing a combination of broadleaf herbicides, such as 2,4-D, dicamba, and mecoprop (MCPP), are effective and safe for use on turfgrass.
Glyphosate is a non-selective herbicide that will kill all plants it touches, including desirable turfgrass, making it unsuitable for use in the middle of a lawn. Because the waxy cuticle reduces herbicide effectiveness, adding a non-ionic surfactant is recommended to help the chemical adhere to and penetrate the foliage. Mowing the weeds shortly before application can increase herbicide uptake by exposing fresh cuts, but the area should not be mowed again for at least two weeks afterward.
Timing is the most important factor for maximizing chemical effectiveness, as the plant must be actively growing to absorb and move the herbicide to the bulb. The best times for application are in the late fall or early winter and again in late winter or early spring. During these cool-season periods, the plant actively transfers energy to its underground storage organs, allowing the systemic herbicide to reach the bulbs. Repeat applications over two or more years are necessary to eliminate all dormant bulblets that sprout at different times.
Preventing Future Infestations
Once eradication is complete, long-term control focuses on creating an environment where these weeds cannot thrive. The most effective preventative measure is maintaining a dense, healthy turf with a strong root system. A thick lawn crowds out weeds, blocking sunlight and minimizing the open soil space needed for new plants to establish.
This involves following proper cultural practices, including appropriate fertilization, regular mowing at the correct height, and adequate watering. Addressing patchy or thin areas quickly is important, as these spots are the most vulnerable to weed invasion. Regular monitoring, particularly during cooler months, allows for the spot treatment of any new clumps before they can develop and spread underground bulbils.