If your lawn is filled with tufts of bright-green, waxy, smelly foliage, it may be time to get out the shovel and start digging. Wild onions are invasive plants, spreading year to year both from seed and bulb. A multi-tiered plan of action is the best way to eradicate wild onions.
Step 1: Address the issue in the early spring and again in the fall. Wild onions (and wild garlic) are perennial plants that grow through the winter and produce flowers, bulblets and seeds in the early spring. Plant foliage dies back in the summer, leaving bulbs lurking beneath the ground awaiting cooler weather to sprout again.
Step 2: A single wild onion plant can produce dozens of seeds. Mowing down or cutting back onions before they bloom will eliminate their spread by seed, but will not stop their reproduction of underground bulbs.
Step 3: Chemicals such as 2,4-D and glyphosate can be somewhat effective, but they tend to roll off the waxy leaves of the plants. Instead of spraying, brush the chemical directly onto freshly cut foliage.
Step 4: Digging plants out completely is by far the best way to eradicate wild onions. The bulb set beneath the ground is typically larger than the footprint of foliage above the ground. Water the area thoroughly and begin digging several inches away from the plant with a small shovel. Dig beneath the initial bulb set to capture as much of the plant and surrounding soil as possible.
Step 5: If possible, kill any remaining bulbs by pouring boiling water into the newly dug hole. Boiling water will kill any plant it comes in contact with. Poured directly onto existing foliage, boiling water will kill the apparent plant, but may not eliminate all of the bulbs beneath the soil.
Step 6: Bulbs and seeds added to a compost pile will flourish. Dispose of plants, bulbs and soil in the trash rather than the compost bin.
Step 7: Weeds tell us a lot about soil conditions. Wild onions prefer alkaline soils with fewer nutrients. Test the soil to see if adding lime may solve the problem. Spreading compost to increase the nutrient value of the lawn will also help reduce the onion population.
Step 8: Consider borrowing a pig to root out wild onion and garlic bulbs. The pig will destroy the lawn, but at least the onions will be gone!