Evergreen browning — To prune or not to prune

Horticulture Hints

This spring, you may have noticed many evergreens with brown needles, brown needle tips or branches. One may assume this damage was due to cold winter temperatures, but most likely the browning was caused by another type of winter injury – desiccation.

Desiccation occurs when the leaves and needles of evergreens, which remain functional throughout the entire year, lose water due to transpiration. On those warm winter days the plant becomes active, the lost water cannot be replaced, as when the ground is frozen, as there is no water available for the roots to take up, and needles brown and tissue death occurs.

Research studies also suggest that desiccation alone does not cause browning of needles, but a combination of environmental stresses. Interaction of cold temperatures, with frequent freeze/thaw cycles, and rapid cooling and thawing rates all play a part in causing winter injury.

Winter injury is most commonly found on those portions of the plant which receive the most sunlight during the winter months, which explains why any “browning” or “burning” is usually noticed on the south or southwest side of evergreens.

What to do? Wait to prune out any browned areas from evergreens, as these branches may recover. Watch for growth of viable buds that may have escaped winter injury to produce new foliage. To encourage new foliage production, make certain plants receive adequate moisture – once the deluge spring rains occurring in many areas has ended.

Did you know? The key to reducing this type of injury is to protect the evergreen foliage from temperature extremes. Avoid late summer pruning which will encourage tender new growth which is more susceptible to damage. Planting in sheltered locations, screening plants with burlap or snow fence, and a good watering in late fall before the ground freezes helps to prevent unsightly foliar browning.

Horticulture Questions? Contact McCormick at yvonne@iastate.edu for information or advice.