In areas where winters are especially cold, ground covers might benefit from a winter mulch. A mulch applied at the time of a new fall planting will prolong the time it takes the soil to freeze, giving the plants a little more time to adapt to harsh conditions.
With an established ground cover, apply the mulch after the ground is frozen, to keep it that way. Damage to plants occurs when the soil alternately thaws and freezes. A mulch, such as straw or shredded leaves, loosely applied over the ground cover also insulates plants against drying winter winds. Do not entirely restrict air circulation around the foliage, however.