As well as protecting your strawberries from killing frosts, a 3 to 4-inch layer of hay or straw helps equalize temperatures to protect them from thawing and refreezing after an early spring or mid-winter warm spell. Don't mulch with fallen leaves since they tend to compact and smother new growth. Although many cultivars are hardy to 15F (-10C), your winter mulch layer should be applied before the temperature dips to 20F (-6C) to protect new growth from killing frosts.
Strawberries are very susceptible to spring frosts. Although winter coverings of straw or mulch should be removed in early spring, rake them to the aisles to re-cover the blossoms in case frost is in the forecast. Old blankets or sheets can also be used for protection against frost.
Although strawberries are sun-lovers, their roots need cool, moist soil. Mulch is the best way to achieve this compromise and it also helps keep runners in check and weeds under control. Nevertheless, do not use the straw that covered your strawberries over the winter. Instead, when danger of frost is past, either remove it or work it into the soil. Apply fresh mulch, keeping about one inch from the crowns to prevent damping off.