If onion grass plagues your landscaping areas with its unwanted and virulent growth, take decisive steps to eradicate this invasive plant from your growing areas. Because onion grass spreads both by reseeding itself and by the cormlets reproducing beneath the soil, a gardener must actively strive to kill onion grass to prevent it from spreading. Dig up the entire plant by hand or apply glyphosate to the undesired onion grass.
Use the weeding fork to dig up the onion grass manually from the soil. Make sure you remove the entire cormlet (root system) from the soil and discard the entire plant into the garbage bag. Continue digging up and removing all of the onion grass plants you find growing in your landscaping areas.
Choose a sunny and calm day with temperatures over 60 degrees Fahrenheit and apply the glyphosate to the onion grass area. Saturate the entire planting area well with the glyphosate. Be aware that the glyphosate will effectively kill almost any plant it contacts. If you have other grass, groundcover or ornamental plants growing nearby, you can easily damage these plants with the glyphosate if you are not careful.
Watch the onion grass growing area vigilantly after you begin the eradication process (whether you are manually or chemically eradicating). Continue to pull the onion grass as it appears to prevent it from reseeding itself. Wait three days after applying the glyphosate and if you do not see the onion grass visibly withering within that period, reapply the glyphosate using the same method.