Growing Together: Rabbit damage was prevalent this winter
Rabbits have a good thing going. They distract us by masquerading as the cute candy-toting Easter Bunny or Bambi’s buddy Thumper, while behind our backs their kinfolks are devouring everything in our landscapes from apple trees to arborvitae.
I’d be more soft-hearted if their never-ending nibbling didn’t cause millions of dollars of damage to trees and shrubs every year. Rabbit damage appears heavier than usual this winter, based on the high number of emails I’ve received, plus extensive damage in our own yard.
Greater-than-normal damage occurred because rabbits were able to begin feeding at the base of plants and continue upward as snow accumulation gave them a higher platform from which to nibble. As snow became deeper, rabbits could reach into the branches of trees, especially younger low-branched trees.
Yards protected by fencing were made vulnerable as snowdrifts allowed rabbits entry across fence tops. Heavy snow also concealed many alternate food sources at the ground level, driving rabbits to seek out landscape material.
The potential for recovery depends on the type of plant and type of injury. The following are ways to assess damage to the trees and shrubs most commonly injured.Deciduous shrubs
Types commonly consumed by rabbits include rose, spirea, dogwood, hydrangea, lilac, aronia and alpine currant. Luckily, these shrubs can tolerate severe damage and usually recover fine, as the rabbits essentially prune back the shrubs for us.
If rabbits have simply consumed twigs from the top down, shortening the branches, the shrub should recover without long-term damage. If instead the rabbits have gnawed away the bark, exposing the white wood inside, the branches above the point of injury will likely die, and those branches should be pruned to a point below the damage.
The shrubs mentioned can be pruned to 4 to 6 inches above ground level, and rebound better than ever if rabbits haven’t consumed everything down to the roots.
Arborvitae, with their soft, flat-type foliage, are rabbit candy. The lower green foliage is often completely consumed as high as rabbits can reach. The arborvitae usually survives as the upper portion grows unharmed, but the base is left bare and unattractive. Foliage usually does not regenerate on these bare twigs and branches. If rabbits also gnaw the bark away and don't just eat foliage, branches may die.
Evergreens can’t regrow or be rejuvenated by heavy pruning the way deciduous shrubs can. It’s a judgment call whether to remove an arborvitae whose lower portions are naked from rabbit feeding while the top remains healthy.
Rabbits are drawn to the sweet bark of fruit trees, flowering crab apples, Canada red cherry, hydrangea trees and dwarf lilac grown as a tree form. If snow depth allowed rabbits to graze the tips of branches, damage can be minimal, other than possible loss of flower and fruit buds. More serious damage results when rabbits girdle the main trunk and large scaffold branches by chewing the bark in a continuous circular band down to the white wood beneath.
Severe girdling usually kills the tree. No pruning paints or sealers can heal such damage. Girdled trees occasionally leaf out from stored reserves but decline by midsummer, and replacement is the best option.
There is a way to save girdled fruit and shade trees, well worth trying and with little to lose. Longtime North Dakota State University plant pathologist Jim Walla, now operating Northern Tree Specialties, recently reminded me of this option for tree repair.
Jim says, “Bridge grafting can be done to reconnect the lower and upper parts of a tree. When successful, the tree slows down for a couple years, but then gets back to normal growth. I've tried it a few times with very good success with apple and birch trees. There are several videos showing bridge grafting methods on YouTube, and supplies (sharp knife, stretchable wrap) are either things you already have or can easily get. It can be very satisfying to rescue a tree with this method.”
Bridge grafting is done in spring, when the bark is “slipping,” using pencil-diameter scions collected from the upper branches while the tree is still dormant and stored in the refrigerator until grafting time. These scions are inserted into the bark with one end above and one end below the damage, creating a bridge, or bypass life support, for the tree.
A thorough description of the process can be found by searching online for the University of Connecticut’s bulletin “Trees: Bridge Grafting and Inarching.”
As Jim Walla suggested, an online search for bridge grafting videos provides several easy-to-follow guides.
Don Kinzler, a lifelong gardener, worked as an NDSU Extension horticulturist and owned Kinzler’s Greenhouse in Fargo. Readers can reach him at email@example.com.