Garlic Growing

I was surprised this morning to walk into my backyard and see shoots coming out of the earth in my self-watering containers.

Garlic and a corner of clover

I got a bulb from the farmer's market last fall, figuring they would have to use a variety that grows well in New England.  I planted the individual cloves and waited. But when I last checked in the fall, the dirt looked as though something had been rooting around in it so I assumed my garlic was gone.  Now my only question is: when do I dig them up?