We all love boxwood for the beautiful evergreen (and deer-resistant) foliage, but winter injury and discoloration can certainly occur. In this newsletter and the next, we’ll discuss some common issues – fitting, considering the winter we’re having (with more yet to come).
We divide cold damage into two camps: frost damage that occurs in fall or spring, resulting in light die-back of the newest growth; and more severe freeze damage because of unusually low or prolonged cold temperatures. Buxus species and/or cultivar cold hardiness is important to note, as there is a fairly broad range of cold tolerance among species. The degree of damage can vary by exposure (sun to shade) and the relationship to topography or structures. Boxwood with southwest-facing, full sun exposure seem to be at greater risk of damage.
Maintenance timing matters as well: early spring or late summer pruning or shearing can stimulate new shoots that will get damaged if there’s not enough time to harden off before a frost or freeze.
What does cold damage look like? Pale- to straw-colored, desiccated foliage and branch tips, usually at the top and outer tips of the plant. Fresh young shoots are especially susceptible (recall boxwood blight symptoms often first appear in the interior lower branches and base of the plant, as spores spread by rain splash). Additionally, an extreme freeze event in fall or spring can cause splitting of bark - resulting in dead limbs. Snow cover can be fantastic for protecting both foliage and branches if it’s a strongly branched plant.
This lovely cloud-style planting of Buxus microphylla ‘Green Pillow’ (Zones 6-9) is in full sun located on the west side of the residence. Sun and wind conspired with an extended hard freeze to desiccate the upper, outer foliage. Once growth resumes in the spring, the plants may benefit from a bit of shearing.
NewGen Independence® (Buxus ‘SB 108’ PP28888) (Zones 5b-8). Last pruned in July, a warm, wet September encouraged a few fresh shoots. Alas, an unusual early-October frost blasted the tender growth. Simply snip these pale shoots off once the danger of frost has passed in the spring.