A tough weed to control. The link has some ideas.

Here is a link that might be useful: link

I used round up on mine prior to their forming flowers, that worked

Weed killers are temporary, and not very environmentally correct, solutions and if the soil conditions that permitted the growth of these is not corrected they will come back. Any "weed" likes certain soil conditions and we need to learn what those are and which soil conditions the plants we want much prefer and make our soil into that and then we will see fewer of those problems without poisoning our environment.

True wild onions and garlic are edible... eating weeds is the best revenge....

It's easier to pull weeds after a good rain, but if it's still too hard to dig or pull them out, just keep them mowed, & eventually the bulb will die.

I'm considering using either a vinegar solution I've read about or a 2, 4-D: 2, 4-DP mix. The problem is the onions are growing up through my blue rug juniper. Does anyone know if either of the above solutions will harm my juniper?

2, 4, D, Dicambra and most all of those "weed" killers are for braod leafed weeds, not the grass like "weeds" of the wild onion/garlic type and those poisons are not very environmentally acceptable. Change the soil conditions where these types of plants are growing and they will be less likely to grow there. Spraying some kind of poison is simply a temporary fix that will need to be repeated, often.