They should be fine. Over in the allium forum you will find several zone 4 growers that have many years experience and will all say cold will not hurt them. Here in NC I am still planting but some of mine have already come up 6-8 inches. We often get alot of growth during the fall and winter. We hardly ever get below zero but when we do the garlic is fine. It will be a couple more weeks before I get my 30,000 plus cloves in the ground so I do know the time and hard work you put into it. Don't worry things will be fine and I hope you have a wonderful summer harvest.
The Garlic Lady

WOW!!!!!, Garlic lady, 30,000!! Just wondering what is your spacing for garlic?

Mark

Our spacing in six inches (eight for elepant shallots and kettle river giant) . I have a six inch planting board with marks every six inches and an eight inch with marks every eight inches. I usually get 6 across each bed (4 for the eight inch varieties) our beds are about 4 foot wide and 100- 150 feet long. We leave about 3 feet between each bed. So we get alot of garlic in very little space. Which means less to mulch and less to weed.
The garlic lady

i get 6 or 7 rows across with 100ft beds.next year we will be adding 4 new beds.peace

This is slightly off-topic, but here is a FABULOUS garlic recipe:

MARINATED GARLIC

30 cloves garlic, peeled*
1/2 cup olive oil
1/4 cup lemon juice
1/4 cup white wine vinegar (I use Champagne vinegar)
Salt and pepper to taste
4 sprigs fresh oregano or 1/2 tsp dried

Blanch the whole cloves of garlic in boiling water for 5 minutes; remove, and plunge into cold water. Drain and dry off the garlic.

Mix the remaining ingredients (except the fresh oregano sprigs) in a blender until emulsified. If using dried oregano toss it in with the oil and vinegar.

Put the cloves in a jar and cover with the marinade, tuck the sprigs of oregano into the jar. Cover and allow it to marinate for at least 5 days in the refrigerator. Serve as is for a snack or side dish or add to a green salad.

Don't be surprised if a couple of people polish off the whole batch in one sitting! I had tried several other marinated garlic recipes before this one and was not happy with the results. This one is perfect!

*NOTE: You can double the garlic cloves and will still have enough dressing to cover. The marinade makes a fantastic salad dressing after you use up the garlic.