Garlic plants can withstand cold weather as long as they are not exposed to a sudden drop of freezing temperatures. To help protect garlic from sudden drops in temperatures, apply a thick layer of mulch such as straw mulch (seed-free); a minimum of 4 inches is recommended, and thicker in regions with harsh winters (up to 8 inches). In the spring the mulch can be pulled back to allow the soil to warm up faster and also helps avoid excess moisture, which can cause rot. Another benefit to mulching is weed control. Garlic does not like to compete with weeds and it will suffer if weeds are not removed. You should not be applying any nitrogen fertilizers over the winter as that will lead to an increase in top growth. After weeding and mulching, now you just have to wait until the spring. Once spring arrives and the soil starts to warm and snows melt, pull back the mulch and feed with an all purpose fertilizer, bone meal or another mix that is high in phosphorus.
For more information on caring for your garlic over the spring, click here.
We have many other tips for winter gardening as well in our Resource Center.