As long as your friend chooses the right varieties, I think garlic will do just fine in zone 4. There are several folks on this forum that grow hardneck garlic in zone 4 - from northern New England through the upper Midwest - so it's definitely possible and with good soil, fall planting and a little help from the weather, your friend should get really good yields. Encourage them to give it a shot ... garlic is one tough plant.

Here is a link that might be useful: Minnesota garlic for cold climates publication

Thanks so much for the information and link. My friend will be very happy! :)

I grew my first crop of garlic in Zone 4 this summer--& just harvested 24 beautiful plants. What I did was go to my local farmer's market last fall and buy heads of two varieties that the farmer had grown locally (i.e., in my zone). I planted the cloves in October and was delighted to find them green and gorgeous when I returned to my garden (from the city) in March--when all else was brown and dormant.

Perhaps your friend can find good, local varieties--or locally adapted/appropriate varieties by paying a visit to the nearest farmer's market in the late summer/early fall.

I harvested my first crops in July. I amended my soil heavily with compost and planted Inchellium Red (softneck) Chesnok Red and Red Czar (hardnecks) in October and mulched heavily with straw. They came out great! Very satisfying to grow and great taste!
Sally