There are dozens of wild onion plants in the bed with my vinca and hosta. How can I get rid of them without killing the vinca and hosta?
Brought to this country by settlers with a yen for onion flavoring, wild onion (and wild garlic) has spread and become a nuisance in many gardens. They reproduce abundantly and there are few ways to get rid of them.
The first treatment, and the cheapest, is to get out and pull the onions up as soon as you see them in the spring. By mid-April the stems may be as much as 8 inches tall or taller. By then, they've had plenty of time to store more energy to keep going for another year. The earlier you get to them, the better. The important part is not to worry about getting the whole bulb. It's enough to get just the green part ... just do it as early in the growing season as you can.
The second course of action is to paint each stem from March to mid-April with either 2, 4D or dicamba, both of which are available to home gardeners. The stems will die back.
Neither method is particularly effective immediately. When you kill or pull the stems early enough, less energy is sent to the bulb to grow or reproduce. It doesn't kill the bulb. So, next spring you have to get out early and go through the same drill. And the spring after that. Eventually, the bulbs will fail and you'll have a clean bed with nothing but your vinca and hosta.
That said, it's important to remember that if you skip a year, you do not pass go and you do not collect $200. You have to start all over again.