We’ve been observing wide spread winter injury on Rhododendron and Holly in the Lakes Region this spring as the snow and ice begin to recede. Cold drying winds over the past several months are partially to blame for the damage, but there are other factors which have certainly contributed to this plight.
Desiccation is the evaporation of water in vapor form from foliage and plant stems. Although this is a year-round and daily occurrence, winter desiccation (also called winter burn) can be particularly stressful on broad leafed evergreens which are the most susceptible because they have a greater surface area through which to lose water compared to deciduous plants. When the ground is frozen solid and freezing temperatures are accompanied by high winds, the exposed plants continue to lose moisture without being able to replenish the supply.
In the two pictures, you’ll see that the foliage at the bottom of the plants is unaffected due to the snow cover protection from the wind. Evergreens that have suffered from winter desiccation typically have beige to brown leaf edges that are curled, or they may show red or purple discoloration.
The stage was set last summer with drought conditions, so broad leafed evergreens went into the winter with a major disadvantage. Younger plants with shallow root systems and plants that have suffered injury in prior years are the most vulnerable. The plants survival is based on the moisture reserve stored up in the roots, branches and leaves.
We recommend delaying pruning chores a bit this spring so that the toll of winter injury can be properly assessed. Dead tissue can be removed anytime, but cutting into live tissue leaves the remaining stem more vulnerable to further drying. Be sure to wait until after shrubs leaf out if you are unsure whether or not a branch is still living. Corrective pruning along with recommended fertilization and proper watering will often help these plants recover.
Rhododendrons do not like soggy soil, so be careful not to overdo it on the watering.