The strawberry is hardy. The roots will live through the severest winter, but it is generally believed that if the leaves are preserved through the season green until spring it is better for the crop that is to follow. Hence a light covering of straw is a benefit, where the winter is severe enough to destroy the fully exposed leaves. It is not the frost, but the sun which does the injury - hence a little straw serves the double purpose of shading the leaves and keeping the roots from being drawn out.