Garlic appears to have been cultivated by humans for so many millennia that natural pollination is normally a failure in this day and time.
At the same time, humans have inadvertently selected garlic for the ease of vegetative propagation (from the planted cloves).
I do not know what the mean frost-free growing period is, here at 53N. In the valley, the microclimate does tend to funnel cold air frosts
in both the spring and the fall. Can't predict from one year to the next except that there is a very large annual crop of garlic.
By that I mean hobby gardeners growing crops of 1,000 - 2,000 plants.
Spring planting seems to produce smaller, sweeter cloves. Fall planting produces much more robust and larger heads which have better after-harvest storage qualities.
I buy both, locally. Right now, I have some spring-planted heads, not too stinky. Have an order in for 3kg in the fall harvest. Quite pungent, to say the hleast.