Bradford, Chanticleer and other ornamental pear trees have got to go. While Chanticleer flowering Pear might have been tree of the year in 2005, cities are asking their residents to cut down their flowering pear trees. Some cities have offered a buyback program where you can get a native tree to replace the chopped down tree. These ornamental trees are marked as invasive in 29 States and that number is predicted to grow. So how did Bradford Pears go from suburb darling to unwanted invasive?
To understand the current invasion we must start at the beginning, with the plant species that Bradford is derived from, Callery pear (Pyrus calleryana) a small flowering tree native to China. These trees were originally imported by the USDA to America as a solution to an agricultural problem.
In 1919 American commercial fruiting pear orchards were being devastated by a bacterial disease, fire-blight. Frank Reimer, a plant scientist at the USDA, hypothesized that the Callery Pear, which has a natural resistance to fire blight could be used as a grafting rootstock for commercial fruit pear trees so that it could pass this resistance onto the fruit bearing tree.
With the help of the plant explorer Frank Meyer, Reimer imported pounds of seed from several different regions in China. However, this was not an easy task because “the trees were very widely scattered, they were often quite small and as such produce individually but little fruit.” as Meyer reported to Reimer. On the other hand, these trees seemed to be able to grow anywhere. When collecting the seeds Meyer recorded and photographed them growing in hostile conditions: barren rocky mountain slopes, screes and the edges of river and ponds with roots fully submerged in water.
To test these specimens' suitability as rootstock, several orchards of Callery pear trees were planted at research centers in Medford, Ore. and Glen Dale, Md. However, it was not until the 1950s that they were starting to be considered an ornamental tree, and the Bradford cultivar was developed at the Glen Dale Maryland Center.
Horticulturist John L. Creech noticed one tree that he considered particularly promising as an ornamental tree. Its branches formed an attractive shape, produced flowers early in the spring, bright glossy leaves in the summer, and bright red foliage in the fall. This particular tree was still hardy and seemed to weather storms without breaking apart better than the other Callery trees in the research orchard. Most importantly, unlike its more wild cousins, this one didn’t have long thorns.
After testing them in a D.C. neighborhood, they were released to the nursery trade in 1960 under the name Bradford Pear. They were an instant hit, their uniform cotton candy shape and low maintenance made them the perfect tree for an expanding suburbia. In 1998 alone over 1.5 million Callery Pear trees were sold totaling over $30 million dollars.
Bradford Pears’ weaknesses became apparent fairly quickly. When frost and storms hit the trees they would just fall apart. The branches tend to grow in narrow V joints to the trunk, often with several branches growing from the same place. As the trees get taller and the branches get heavier the weak joints will start to split. These trees have a short lifespan only reaching 15-20 years before they rip apart under their own weight.
To try to solve this problem new cultivars were introduced to be less prone to breakage. These different cultivars were developed from Callery Pears that were descendants of trees imported from different regions of China.
Pear trees are self-incompatible, meaning they cannot fertilize themselves. A single pear tree on its own, will not create fruit. If a street is lined with trees that are all of the same cultivar (clones), none of the trees will produce fruit. This was originally part of the appeal of these trees: they wouldn’t drop messy fruit all over a yard like a crab apple or cherry tree.
All the trees of a cultivar are genetic clones of a single original tree. Instead of being grown from seed, they are propagated by grafting where a cutting is taken from the desired tree (scion) and attached to a trunk (rootstock) that has been cut with a notch near the base. The site of the cut is then wrapped in tape or wax while the two parts fuse and grow in to each other. The top of the new grafted tree will be a genetic clone of the original tree while the roots will have a different genotype.
But when new and “improved” cultivars started being introduced in the late 60s, they were often placed nearby already planted Bradfords. Now, there were genetically distinct trees in range to pollinate each other. A Bradford pear can’t pollinate another Bradford Pear but a Bradford and Cleveland Select Pear tree will cross pollinate and produce fruit. Compounding the issue is that the different cultivars are sourced from trees that originally came from desperate regions of China and be found near each other in the wild.
Since these commercial Callery Pear trees are two genetically distinct plants fused together by grafting, one single tree has everything it needs to fertilize itself. Often sucker branches will sprout from the rootstock when the roots are nicked by lawn mowers or even just randomly. These branches can grow flowers with pollen that is genetically compatible with the flowers of the upper half’s branches. In a genetic analysis of invasive Callery Pear populations 17% of trees surveyed were shown to a have at least one rootstock parent.
The fruits mature in early to late fall when starlings and other birds will eat them and spread the seeds in the fruit far from the parent tree. These wild pears tend to flourish in open disturbed fields, like the sides of highways and reclaimed grassland prairies. The traits that made them desirable as ornamental trees, fast growing, can survive in harsh conditions, and abundant flowering, also help them take over and compete with native plants.
Wild Callery Pears grow quickly and start to flower and bear fruit after only three years. Since they can flower and sprout leaves earlier in the spring than most native plants, Callery Pears will quickly start to crowd out other trees for light. This creates dense thickets of Callery Pear monocultures, which can be hard to remove. Not only does the tree need to be chopped down but the trunk must be removed or killed with herbicide. Otherwise the roots will keep sending up sprouts trying to reestablish the tree.
Even once the adult trees are removed the problem isn’t fixed. Callery Pear seeds can become dormant if exposed to warm weather in late winter.This creates a seed bank in the soil, so that after the adults are removed, seeds already present in the soil will sprout up to take their place. Even after Callery Pear trees have been removed from an area, it can take years of removing seedlings before they are finally gone and native plans have a chance to grow. It’s hard to put an invasive species back into Pandora’s Box once it’s escaped the garden and has started to spread.
If they had not fit into the idea of a perfect lawn, it is unlikely that they would be spread them across the country. Even now it is still possible to purchase these trees from large commercial nurseries and hardware stores. But initiatives like "buyback" programs and public education can help keep their spread from accelerating. For more information, Missouri Botanical Garden has this list of resources on the removal of Bradford/Callery Pears and native alternatives to plant instead.
Casagrand, T. (2019, April 19). Callery Pear Buy-back Event in St.
Louis, MO - April 26, 2019. Retrieved May 20, 2019, from
Culley, T. M., & Hardiman, N. A. (2007). The beginning of a new invasive plant: a history of the ornamental Callery pear in the United States. BioScience, 57(11), 956–964. https://doi.org/10.1641/b571108
Culley, T. M., & Hardiman, N. A. (2008). The role of intraspecific hybridization in the evolution of invasiveness: a case study of the ornamental pear tree Pyrus calleryana. Biological Invasions, 11(5), 1107–1119. https://doi.org/10.1007/s10530-008-9386-z
Culley, T. M., Hardiman, N. A., & Hawks, J. (2010). The role of horticulture in plant invasions: how grafting in cultivars of Callery pear (Pyrus calleryana) can facilitate spread into natural areas. Biological Invasions, 13(3), 739–746. https://doi.org/10.1007/s10530-010-9864-y
Hardiman, N. A., & Culley, T. M. (2010). Reproductive success of cultivated Pyrus calleryana (Rosaceae) and establishment ability of invasive, hybrid progeny. American Journal of Botany, 97(10), 1698–1706. https://doi.org/10.3732/ajb.1000113
Higgins A., (2018, September 18) Scientists thought they had created the perfect tree. But it became a nightmare. The Washington Post. Retrieved from https://www.washingtonpost.com/lifestyle/magazine/how-we-turned-the-bradford-pear-into-a-monster/2018/09/14/f29c8f68-91b6-11e8-b769-e3fff17f0689_story.html
Unknown. 1917. “Pyrus calleryana. Dwarf wild Calleryana pears. neg. No.
13267. .” Special Collections, USDA National Agricultural Library.
Accessed May 22, 2019,