By: Sandy Feather ©2009
Penn State Extension
Q. How can I get rid of wild onions in my lawn? I pulled them out last year, but they have come back with a vengeance!
A. Wild garlic (Allium vineale) and wild onion (Allium canadense) are closely related and similar in appearance. The easiest way to tell the difference is that wild garlic's leaves are hollow, while those of wild onion are not. Both are difficult to control. They are perennial, coming back year after year from underground bulbs, much like daffodils and tulips. You can eventually get rid of them if you dig them out with a trowel. But you have to be relentless; as soon as you see a leaf sprout, dig it out. Any tiny offset bulb or even piece of bulb left in the ground will resprout into a new plant.
It could take years to eradicate them this way, but it can work. They may have come back with a vengeance because you left lots of small bulbs behind, or pieces of bulbs, when you pulled them out by hand. It is more effective to dig them out with a trowel to make sure you get the bulbs.
You can compost the leaves, but send the bulbs out with the trash or burn them. Most of us do not compost intensively enough to heat the piles up sufficiently to kill most weed seeds and vegetative structures.
Despite their grassy appearance, onion and garlic can be controlled with herbicides labeled to control broadleaf weeds such as dandelions. But they are a challenge because the waxy coating on their leaves causes herbicide applications to run off instead of being absorbed. Certain liquid formulations will be much more effective than granular weed-and-feed products. Be sure to wet the foliage thoroughly when you are spraying, and be aware that you will need to make repeated applications.
The active ingredients of standard broadleaf weed control products include 2, 4-D; 2, 4-DP (dichlorprop); MCPP (mecoprop); and dicamba. Most herbicides available to home gardeners are amine salt formulations, which are less likely than ester-based ones to volatilize and drift off target, especially during hot weather. However, ester formulations are more volatile, which makes them better able to penetrate the waxy cuticle of leaves.
They are not restricted-use products that require an applicator's license to purchase them, but they are professional-use products that usually come in 1-gallon and larger sizes -- more than homeowners should ever need or use. You may sometimes find ester-formulation herbicides in quart sizes at farm supply stores such as Agway. Call before you make a special trip.
Although many perennial weeds are best controlled by late summer-early fall herbicide applications, mid-spring is recommended to control wild onions and garlic.
Another unusual recommendation is that you should mow prior to spraying the herbicide. The cut surfaces will absorb the herbicide better than an intact leaf.