Remove winter mulch in late winter or early spring when you observe new growth under the mulch. (Dig around in the mulch periodically to check for growth.) If you see mold developing on the plants, it's time to pull back the mulch. Keep in mind that winter mulch protects plants from sudden temperature changes, so acclimate your plants by pulling off the mulch gradually, over a period of days, as the plants show signs of new growth. This allows light and air to reach the new growth slowly, eliminating the chance of shock to your plants. Do keep some of the mulch handy, just in case frost is predicted and you need to protect the tender new growth.