You have no doubt noticed all the white flowering trees that have been putting on a show the past couple of weeks, which I think have bloomed early this year because of the warm winter we’ve had. They are Bradford pears, which are very popular landscape trees, noted for their beautiful flower blitz, symmetrical round crowns, and supposedly sterile and won’t produce messy fruit to clean up. “Supposedly” is such a negative word and I hate to use it, but driving down the road it’s easy to find Bradford pear spreading beyond yards and can now be found in fencerows, along roadsides, and even into farm fields. They have in fact become invasive. So what the heck?
Bradford pear is a cultivar of Callery pear, a native to China. When a breeding program finally produced a tree with the above mentioned desirable qualities, the Bradford hybrid was grafted onto pear rootstock in vast numbers to supply the huge demand for the tree. So almost all Bradford pear nursery trees are clones and genetically identical (referred to as genotype), and were found to be self-incompatible, meaning they cannot fertilize themselves to produce viable seed.
But (another word I hate to use) life on our planet wants to make babies, and so nature found a way. Bradford pear limbs are weak due to a branch structure that produces narrow crotches. This allows limbs to shear off easily along the wood grain when heavy snow or wind events occur. A solution was sought and cultivars were bred using an Asian pear (a different genotype) that produced a stronger limb structure. So when this variety was planted into landscapes, it could cross pollinate with Bradford and both could produce heavy crops fruit (small, speckled berry-like) that contained viable seeds. Another way cross pollination can occur is graft jumping. As mentioned, Bradfords were produced by grafting cuttings onto seed-grown root stock of another pear variety. It’s not uncommon for rootstock to sprout and grow branches that can produce flowers. When that happens the tree now has flowers from two different genotypes, and can thus cross-pollinate and produce fruit with seeds.
Birds come along and consume the fruit, then fly off and poop out the seeds, and so trees are now growing where they don’t belong. They are strong competitors with native plants and can become a nuisance. They grow a massive root system that is hard to kill out. They can produce thickets that are very hard to get rid of once established. Some wild trees have genetically reverted back to ancient Chinese Callery pears that can have long sharp thorns that are nasty to mess with. There are few insect or disease problems to keep the Bradford population in check. There is some thought that the tree is allelopathic, meaning it can produce chemicals in the soil that prevent other plant seeds from germinating. Bradford appears to be poised for world domination.
Wisdom dictates not using Bradford pear your landscape. Alternative tree selections that produce early white flowers are serviceberry and wild plum.
Steve Roark is the area forester in Tazewell, Tennessee, for the Tennessee Department of Agriculture, Forestry Division.