Rhododendron Winter Damage and Prevention
Frost causes considerable damage to leaves, stems, buds, and flowers of some rhododendrons. On damaged plants leaves will be distorted, curled, and may grow only on one side of the main vein. Part or all of a winter-damaged leaf will be brown-colored. If too unsightly, remove the damaged leaves.
Some rhododendrons protect themselves from winter dehydration by drooping and curling their leaves as temperatures decrease. Leaf movement occurs rapidly and it is reversible as temperature warms.
Frost also will cause the bark of affected stems to split longitudinally near ground level...even peeling away. This typically happens in early fall or late spring when the plant is not fully dormant. Often these symptoms are overlooked and damage only noticed at a later date. If noticed recently after the injury and before the bark has had time to dry out the area can be wrapped with galvanized wire or a non-sticky wrapping. Check the wrapping monthly and remove the wire when the repair is successful.
Cold weather may cause branches to appear to be dead. Wait until late spring then scratch the bark on dead-looking branches. If there is green wood underneath, the branch is still alive, leave it in place. If it's brown underneath, the branch is dead and can be pruned off.
Cold weather can kill flower buds. Dead buds are brown-colored and easily break off. Often rhododendron buds are less hardy than other parts of the plant. Choose varieties that are bud cold-hardy for your area.
Because rhododendrons roots are very shallow, it's important to use a thick layer of mulch to provide protection from the cold. It'll also slow water evaporation from the ground, helping plants to stay hydrated. On warm days water your plants so they have a chance to survive cold periods.
A windbreak made from burlap, lattice or a snow fence can help prevent damage from winter's drying winds.