Otherwise, a winter mulch is helpful, but should be applied after the ground begins to freeze. Caring for Your Lilies Leave the mulch in place until the danger of hard frost, which can damage the shoots and kill the flower buds of some tender lilies, has passed. If lily shoots grow through the covering, remove the mulch, but leave it nearby so you can cover them if a hard frost is predicted. Slow-release fertilizers work well. Always follow label instructions when applying fertilizer.
Lilies usually have few pests, but rabbits and slugs can be a menace to emerging shoots.
Small sucking insects called aphids can also cause problems for flower buds. Carefully wash the affected plants off with a garden hose to remove aphids. A sunny location and careful watering that avoids wetting the foliage will help reduce fungal diseases. Remove old flowers on the plants by carefully breaking them off. Remove old foliage in early spring by cutting down the dead stalks.