The leaves on my Rhododendrons curled and browned in the cold last winter – How can I prevent this?
If the symptoms on these plants were indeed caused by the extreme cold, then the plants have lost moisture through their stoma or pores. Plants stoma are much like our skin pores and moisture can be lost through these in the same way we lose moisture as we sweat.
Plants transpire much like we perspire and the dry cold air wicks the moisture away from the leaves surface. A Rhododendron will try to cut back on exposed tissue and will curl its leaves up much like tubes in reaction to the drying winds. During harsh winters this reaction is usually to no effect. When spring arrives there are many plants including Rhododendron that are suffering from winter desiccation, or drying out, and are in need of some extra time and attention to help recover.
The best preventive measure is to pay attention to which of your landscape plants have been suffering through the winters, and protect them before the winter winds arrive. You can wrap your plants in burlap or you can buy an Anti-transpirant or Wilt-pruf. An Anti-transpirant is safe for the environment and is a waxy type substance that acts as an insulator for the plants. Usually you will mix the anti-transpirant concentrate with water in a clean horticultural sprayer and apply it liberally to the plant tissue both above and below until the product is dripping off of the leaves. For NE Ohio you will want your first winter application of this product on or around November 15th, before applying make sure there has been at least four to five days of forty degree temperatures or higher. This will allow the spray to go on evenly and also allows the product time to dry so it will not freeze to the plants tissue. You will want to repeat this process again on or around January 15th, and be mindful of the temperatures.
You can apply an Anti-transpirant to many plants including; Arborvitae, Inkberry, Rhododendron, Azalea and more. The only draw back is sometimes the second application, the one in January, can cause some buds of the Rhododendron and Azaleas to become glued shut and it is possible to miss out on a few blossoms.
You may apply an Anti-transpirant later than January 15th, if you have a concern for the coming cold, But, you may glue your buds shut.
Roots and leaves of evergreens still need water in the winter, if the temps are above freezing and we have not had precipitation it is always a good practice to water evergreens to keep them healthy and thriving.
