If the plants are annuals, forget it - they only live one year and are dead already. If they are perennial flowering plants, we usually recommend cutting back to about 6 inches in the late Fall, which you can do now, so you can see where the plant will be coming back up in the spring. Their roots should not have frozen if you had them in the ground, so they will come back soon. If they were shrubs, you will actually be doing your winter pruning. Trim back for shape - then whatever is left that does not leaf out can be trimmed back later.