I potted shallots in early January and left them outside in the cold, then
planted them in the ground in late March. When will they start to form
multi bulbs? They're not doing much of anything right now.

Thanks.

Give them a chance. they have a few more months to go yet. I wait until all the leaves have died back before I lift them.When I plant the bulbs I have saved for next year I rarely get any going to seed.
Bigal