Once a good hard freeze sets in one night, a lot of perennial ground covers can be cut back to a couple of inches above ground the level to get rid of the dead top growth. This would include mums, hostas, day lilies, etc. It is advisable to let the growth stay on some plants like lariope and pompias grasses to protect the crown over the winter from snow and ice collecting on them. I will usually cut back the long reeds on the grasses and leave the remaining growth to protect the crown. Covering up roses and the cut back ground covers will protect them from the winter weather and keep the soil at a constant temperature to help avoid thawing and refreeze which can sometimes pop plants out of the ground if they are fairly young and don`t have an established root system. A good winter mulch can be pine needles, or mulched up leaves. Just make sure to remove your winter mulch in the spring once the chance of frost is gone which is usually by April 1st. Keep the leaves cleaned up as they fall. I know this can be a never ending battle as a lot of trees are late this year to drop their leaves with the mild temperatures that we have been having. A few things can go a long way to help out the garden this winter.