“Onion grass” is a common name for several persistent, perennial weeds that frequently invade lawns and gardens. These plants are characterized by a grass-like appearance and a pungent odor when their leaves are crushed. Despite the name, this species is not a true grass but a member of the Allium genus, the same family as cultivated onions, garlic, and chives. It is a difficult-to-control weed because it propagates aggressively and survives harsh conditions, often dominating turfgrass. Homeowners often see it actively growing during cooler months when turfgrass is dormant.
Identification and Botanical Classification
The plants commonly called onion grass or wild garlic are primarily Allium vineale (Wild Garlic) and Allium canadense (Wild Onion). Both belong to the Amaryllidaceae family, which distinguishes them from true grasses (Poaceae family). This botanical difference dictates how the plant grows and how it must be managed.
Wild Garlic (A. vineale) has slender, dark green leaves that are round, hollow, and grow up to 18 inches tall. This species reproduces aggressively through underground bulbs, small bulblets, and aerial bulblets that form in a cluster at the top of the stem. The leaves have a waxy coating, which presents a challenge when attempting chemical control methods.
Wild Onion (A. canadense) is often confused with Wild Garlic, though it displays a structural difference in its foliage. Its leaves are typically flatter and solid, rather than hollow and cylindrical. Another species sometimes called onion grass, Allium triquetrum (Three-cornered Leek), is recognized by its smooth stems that have three distinct, sharp angles.
The underground structure is a complex system of small, whitish bulbs that allows the plants to persist for many years. These bulbs can remain dormant in the soil, ready to sprout new growth when conditions are favorable. This perennial nature and the capacity to produce numerous offsets make complete removal challenging.
Safety and Culinary Applications
Most species within the Allium genus are safe for consumption. Both the leaves and the small underground bulbs of Allium vineale and Allium canadense can be used in cooking, offering a mild, pungent flavor similar to chives or green onions. The aerial bulblets produced by A. vineale are also edible and can be used as seasoning.
These wild Allium parts can be incorporated into salads, soups, egg dishes, or pestos, providing a fresh, oniony taste. Foraging requires caution to avoid misidentification with toxic look-alikes. Poisonous plants, such as Lily of the Valley, can appear similar when young but lack the distinctive onion or garlic odor.
The most reliable safety test is to crush a leaf; if it does not emit the characteristic Allium scent, it should not be consumed. It is also important to confirm that the plants have not been exposed to herbicides or pesticides before they are used in food, as chemical contamination renders them unsafe.
Eradication and Control Methods
Controlling onion grass is difficult due to its unique biology and reproduction methods. For small infestations, the most effective non-chemical approach is meticulous manual removal. Simply pulling the leaves is ineffective because the hollow stems break easily, leaving the underground bulbs intact to sprout again.
To ensure complete removal, a trowel must be used to dig deep enough to extract the entire bulb and any attached bulblets. These reproductive structures must be removed entirely from the soil. Fall tillage in garden beds can also disrupt the growth cycle and expose the bulbs to harsh winter weather.
For larger infestations, chemical control using selective post-emergent herbicides is necessary. Pre-emergent herbicides are ineffective because the plant reproduces primarily from bulbs and bulblets, not seeds. Products containing a combination of broadleaf herbicides, such as 2,4-D, dicamba, and MCPP, are the recommended options for turfgrass.
The waxy, cylindrical leaves of Allium vineale repel liquid, making it difficult for herbicides to adhere and be absorbed. To improve efficacy, the herbicide should be applied in the fall and repeated in the late winter or early spring over two successive years. Applying the ester formulation of 2,4-D shows better results than amine salt formulations because the ester is more easily absorbed through the waxy leaf surface.