Care for daylilies in the winter by digging up the plants, dividing the clumps, and replanting the lilies. Prune down the foliage to within a few inches of the ground, and continue to water the plants for at least a week to help the roots become established before it becomes too cold.
Provided the ground isn't frozen, dig up daylilies in the early winter or late fall, and divide large plants so that each has a generous portion of the roots. After transplanting the daylilies back into the ground, water them well. Trim down the foliage near the base to within 4 inches of the ground, removing any yellowing or brown leaves. Only water the flowers for another week or so, and then discontinue watering during the cold months to allow the plants to go dormant. Only commence watering and fertilizing the daylilies after the last frost of the spring.
To protect the daylilies from the cold and frost, cover them with 2 inches of leaf, straw, bark or pine needle mulch. For areas with hard freezes, add at least 4 inches of mulch to the plants, and water them well prior to the first freeze so that the roots have plenty of water.