Chisago County Master Gardener
Just look around your neighborhood this spring, and you’re likely to see brown needles on evergreens. Spruce, pine, and broadleaf evergreens like boxwood are showing lots of winter burn injury sustained during our severe winter.
Winter burn is the result of water loss in plants during the cold months. The needles dry, die and develop a reddish-brown color. Typically this occurs on branches and needles that are above the snowline. When the snow melts, you discover the top half of the evergreen is reddish brown, while the bottom half, which was under the snow, is still green.
In winter, even if air temperatures are low, sunlight reflected by snow concentrates solar energy on the south and west sides of the plant. This raises the internal needle temperature, ramping up the photosynthetic process.
Additional water is needed during photosynthesis, but if the ground is frozen, the plant is unable to replace the lost water.
If the chlorophyll molecules absorb too much solar energy and it can’t all be used in the photosynthetic process, chlorophyll (what makes the needle green) can be destroyed through photooxidation and not resynthesized when temperatures are very cold. This results in discoloration of the foliage, what we call ‘winter burn.’ If the damage is severe enough, plant death can occur.
Though you might be concerned about brown evergreens, be patient. Before you do any pruning or replacing, see if there is life hidden underneath by scratching the fine branches with your fingernail. If the branch is green, it is living.
You can run your hands over the brown needles, squeezing gently, and they will fall away. In a month or so, new growth should appear.
In some cases, the branches are affected and will not regrow. For these plants, prune away the dead parts.
Regrowth may fill the vacant area, but that could take several years. Some plants with deep damage may be alive but disfigured to the point of needing to be replaced.