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Why did my boxwoods turn brown this winter?
Winter damage occurs on boxwoods (Buxus sp.) when unseasonably warm winter days are followed by freezing temperatures. During the warm period, the plant begins to come out of dormancy and the cambium or conductive tissue begins to fill with additional water. When the temperature drops below freezing, the water freezes. The expanding ice splits the tissue resulting in death of the affected tissue. Cold, dry winds pull moisture from the affected branch resulting in a freeze-dried, "freezer burn" effect. Depending upon conditions, whole plants, just sections of a plant or only the tips of branches may be affected.
Tip burn is quite minor and only affects the tips of branches. Simply remove the dead tips with pruning shears or hand pruners. The plant will recover.
Sectional winter burn or die-out occurs when one or more whole branches die. The most recognizable sign is when the leaves turn pale yellow to almost white. On close inspection, bark splitting from the branches will be evident. Splitting can continue all the way to the base of the branch. Prune these branches back to the point where the splitting stops. Full recovery can take several years.
Winter burn of the total plant is the most devastating. In this case the whole shrub will turn a pale yellow and every branch will have splitting bark. For these plants, the only chance for recovery is to severely prune the plant. In spring after all chances of severe frost are past cut all branches back to a twelve to eighteen inch mound, depending upon the size of the plant. This method is not always successful; be prepared to completely remove the plant if it does not recover.
A recently planted, juvenile boxwood with extensive winter damage is best removed and replaced as recovery of a damaged plant may be very slow compared to the growth of a new, undamaged plant.