If you are growing hardneck -- and you probably are since you are in the north, they will start to grow scapes/flower stalks, which are delicious. If they haven't grown scapes yet, you could still side dress with fertilizer. I think you want something with same three numbers. If you haven't mulched them, do that after fertilizing.
Garlic won't grow in the fall if you plant late or if you get an early hard freeze. Since they didn't get that chance to make a head start they may not grow as fast or big as they could have. There are variety differences, too. I've mostly given up growing garlic that make lots of small cloves -- too much work.