IN NY and NH, same basic climate zone as Michigan, it’s late July/early Aug.
My garlic is just starting to send up the scapes, the flower stalks. I cut those off and give them away. I lot of people like to use them in cooking.
A few weeks after that, the leaves start turning brown from the bottom up. Each leave is one layer of skin on the garlic, so when about half the leaves have turned brown is when you harvest the garlic.
Many thanks to both of you. Last year was our first year, we pulled them in September I think. Looked great, I thought the bulbs could have been a bit bigger.