The term “onion grass” is a common name for persistent, perennial weeds that frequently invade lawns and gardens, most often referring to Allium vineale (wild garlic) or Allium canadense (wild onion). These plants belong to the Allium genus, which includes edible onions and garlic. They are notorious for growing faster than surrounding lawn species.
Defining the Above-Ground Appearance
The most recognizable feature of onion grass is its foliage, which typically grows in dense, upright clumps within a lawn. The leaves emerge from the soil with a waxy coating, giving them a slightly glossy appearance that often makes them stand out from the surrounding turf. These leaves are narrow and grass-like, generally reaching heights between 6 and 18 inches if left unmowed, and they exhibit a color that ranges from a deep blue-green to a dark green hue.
The shape of the leaves is a primary diagnostic feature. Wild garlic (A. vineale) leaves are thin, cylindrical, and distinctly hollow, like a small drinking straw. In contrast, wild onion (A. canadense) leaves are typically flat or slightly V-shaped in cross-section and are solid, not hollow.
Key Identifying Features of the Bulb and Root System
Onion grass grows from small, underground true bulbs, which are often clustered together. These main bulbs are typically covered with a thin, papery, brownish skin, similar to a miniature garden onion. The plant also reproduces by forming offsets, or small secondary bulbs called bulbils, that grow from the base of the main bulb.
The tenacious root system is composed of fine, fibrous roots that extend a short distance from the basal plate of the bulb, anchoring the plant firmly in the soil. The challenge in removing the plant comes from the ease with which these small bulblets detach from the parent bulb during pulling, allowing them to remain dormant in the soil and grow later.
How to Differentiate Onion Grass from Common Look-Alikes
Distinguishing onion grass from other similar-looking plants relies on a combination of tactile and olfactory tests. Many common lawn weeds, such as certain ornamental turfgrasses, can grow in similar clumps but lack the characteristic smell. Any plant that looks like grass but releases a potent onion or garlic scent when a leaf is gently crushed is confirmed to be an Allium species.
Wild garlic often produces clusters of tiny, hard, greenish-white or purplish bulbils at the top of its stem in place of flowers, a feature that wild onion does not commonly exhibit. This terminal cluster of aerial bulbils is a clear visual marker for wild garlic.
It is also important to differentiate onion grass from potentially toxic look-alikes, such as Death Camas (Zigadenus venenosus), which can be deadly if ingested. The most reliable distinction remains the scent test, as toxic imposters do not produce the distinctive sulfurous onion or garlic aroma.