Last week, the column covered problems with our needle evergreens. This week, it is about our broadleaved landscape plants and specifically, what is happening to our boxwoods out in the landscape.
Boxwoods have always been known to need some TLC when it comes to getting them through the normal northern Illinois winter. Like our needled evergreens, boxwoods and other broadleaf evergreens are very alive all winter. Boxwoods are usually sited with northern or eastern exposures, or protected in some way from winter sunlight and winds. Plant breeders have increased their winter hardiness with some cultivars, but certainly not all of them. Protecting them with burlap from the sun or creating a temporary winter windbreak are the common ways to give them what they need. Some gardeners will treat the boxwood with an anti-desiccate before the temperatures fall below freezing and again on a mild day late winter or very early spring. Anti-desiccates seal the leaves by coating them, preventing moisture loss.
The damage this spring has been extensive on old and new plantings alike. If this was a disease, damage would be scattered and symptoms would have been present last summer. What is happening right now is environmental, primarily the severe cold we experienced over winter. Damage is uniform and to varying degrees based on where they are planted in the home landscape. Take a walk around the neighborhood and those differences are readily seen.
If the damage is minor, just leaves at the edge of the canopies will have the brown, burnt look. Those leaves will fall away when 2019 growth begins. In many cases, the entire boxwood is browned and recovery is questionable. If it is just the tips and browning is minor, plants will typically recover like in the past. More damage than that and the 2019 vegetative buds would be killed. Any regrowth will have to come from well within the canopy. Stems and twigs would be the next to go and then the desiccation moves further downward towards the crown. If you take a close look, those stems and twigs will be shriveled.
There is not a problem with replanting boxwood with boxwood. There is a disease known as Boxwood Blight that has been spreading in the United States and so far has not been detected in Illinois. If possible, buy replacements that have been grown in Illinois. At least ask the retailer if the boxwoods for sale have been certified blight-free from the supplier, if not Illinois grown.
When planting, modify the backfill soil with organic matter to increase aeration and drainage. Water them well at planting time and monitor them regularly for water. It will take at least two years to establish, longer for larger boxwood. They will have a limited root system during this time, making them more susceptible to desiccation, especially in the winter.