Experts and BHG readers answer.
How to kill weeds in bulb bed?
I'm afraid that you won't find a selective weed control product that would kill wild onion, but not damage your desirable bulbs. After all, wild onion is a bulb also. You could get good control of annual weeds by putting down a pre-emergent herbicide that kills germinating seedlings, but won't damage established plants. Preen is one brand that is labeled for use with many flowers. Check the label for specific types of flowers that it can be used with. You could also apply several inches of mulch on the bed. Bulbs will sprout through the mulch, but annual weeds would not readily grow through the mulch.
You may also be able to spot treat the weeds with a non-selective herbicide such as glyphosate (Roundup) when the bulbs are dormant, but the weeds are actively growing. As long as none of the herbicide gets on aboveground parts of the bulb plants, glyphosate won't harm them because it is not active through the soil.