The flowering shrub known as rhododendron requires very specific growing conditions, including well-drained, acid soil and a region with a mild climate. However, even when these conditions are met, the rhododendron may suffer from curled leaves.
This occurs in cold weather when the rhododendron tries to retain moisture. Moisture decreases along the leaf edge first, so this area shows the first signs of damage. This condition develops when temperatures drop to near freezing. Plant rhododendrons on the north side of your house or other building, protecting it from excessive sunlight and wind during the cold winter months. Plants generally recover when warm weather returns.
Crown or root rot, a fungal disease of plants, causes problems in wet, poorly drained sites. Identify rhododendrons with this disease by their drooping, inward-curling leaves and wet, black roots.
This fungal disease causes abnormal leaf and stem growth in spring. Leaf thickness increases and leaves curl and bleach to a light green or white colour. Pick the galls off affected plants or apply a fungicide in severe cases.