I wrote this article for TheFruitExplorers.com and decided to cross post it here.
Every year, around this time, social media begins to rumble in uproar over Bradford Pear (Pyrus calleryana). With headlines like “The Curse of the Bradford Pear,” “Bradford pear tree: How the trees can hurt people, then environment,” and finally “I Just Hate Bradford Pear,” it’s no wonder people have it out for them. The trees have NO GOOD PRESS and, unfortunately, it’s much easier for hoards of people to fall in line with anti-invasive rhetoric than to understand who or what they are trying to demonize. In light of this, the time has come to take a stand for this poorly misunderstood tree.
Bradford pear belongs to the species Pyrus calleryana, which is why it is sometimes called “Callery.” This species of pear is native to China, where the range goes from sea-level to 5000 feet in elevation, spanning a thousand miles inland as the crow flies. Cousins of callery pear are also in Northern Korea and Japan, showing an immense climate and site adaptability for the species.
How did it get to the US?:
In the early 20th century, the Pacific Northwest contained many orchards of Pyrus communis, or French pears. These pears were being ravaged by fireblight (Erwinia amylovora), a native bacterial disease, and professor Frank Reimer was pulling his hair out over the potential loss of the West Coast commercial pear industry if a control for fireblight wasn’t found soon. Researchers have long known that Asia’s gene pool for fruit and nuts is much older than European or American genetics, and likely hold resistances or much improved tolerances to pest and disease due to the long and slow co-evolution over time. Reimer knew, from his research, that Pyrus calleryana and Pyrus ussuriensis were inherently resistant, so he put out an SOS to obtain pear seed from Asian regions in order to hopefully find resistance.
Harvard’s Arnold Arboretum in Massachusetts answered his call in 1908, sending plant explorer EH Wilson (aka “Chinese” Wilson) to China to see what he could find. Once there, he collected P. calleryana seeds from 4,000-5,000 feet in elevation and sent them to be grown out in Boston. Many of these proved to be hardy for Massachusetts and many people, including professor Frank Reimer, got excited. Given the potential for Pyrus callerana to save the commercial pear industry in the PNW, the USDA decided to add callery pear to their fruit’s explorer’s collection list.
At the time, the USDA had been going through a period of glitz and glam concerning their plant exploration program. The golden child at the center of this hubub was the darling plant explorer David Fairchild, the person responsible for bringing over German hops, the avocado, and kale (among many, many other things). With his notoriety and prestige, he married into the fabulously wealthy family of Alexander Graham Bell, and was feeling the need to step down from his travels abroad in order to start a family. Instead of Fairchild himself going on the pear mission, he delegated the job to one of the toughest mofos alive: Frank Meyer. Dutch born, Meyer was known for his ability to walk 30+ miles a day, everyday, forever.
This would be no small job, either. According to Arnold Arboretum, 25 pounds of seed would require picking seeds out of 5000 pounds of fruit. That’s the equivalent of 125 bushels of tiny (8.5mm on average) callery pear fruits, which would be maddening to collect by hand. This wasn’t a problem for Meyer, though, as he probably preferred tiny pear seeds to interacting with people. With his marching orders, he set out on this pear mission, writing the following to his boss, David Fairchild:
Once the first batches of seeds were back in the States, they went under commercial pear rootstock monitoring for fireblight resistance. These pear seeds produced vigorous, uniform trees that, when inoculated with fireblight, proved to be the most resistant of any pear tree they had evaluated, by a landslide (double the resistance of Pyrus ussurriensis and far more vigorous). The chart below reveals the results of this trial:
In later studies, Reimer reported that 11% of P. calleryana trunk inoculations showed a severe fireblight infection. Which, by the way, is pretty amazing. When I innoculated my apple seedlings with fireblight ooze, 95% of them showed severe infection or died.
In addition to having stellar fireblight resistance, Callery pears were tested on a variety of sites and were found to thrive in nearly all soil and moisture scenarios, from coarse sand underlain by granite to heavy clay. They also found Callery pears to have a lower chilling requirement than P. communis (French pear rootstock) (source), allowing for it to be grown in more erratic seasonal conditions (which might not have been a big deal then but MAN is that a big deal now). This pear species was seen as the most bomb-proof, resilient rootstock around on which to grow our favorite eating pears, and even produced yields 32% above the same cultivars grafted to P. communis (Source: Westwood, Pear Rootstocks for the Northwest. NAFEX POMONA Vol 3, Number 2, 1970). With the excitement and growing popularity of using callery pear as rootstock, the US continued with seed gathering trips to China for decades.
From Amazing to Pariah, what happened?
First of all, most of what you read about the introduction of Bradford pear (P. calleryana) to America is incorrect, as I’ve just given you the real history above. Outlets like The Grumpy Gardner, a now-retired columnist for all things horticulture at Southern Living Magazine, have done a lot of damage spewing emotion-based information to people who don’t know any better. With little challenge to any of the points ever made, he and others managed to create a culture of emotional reaction surrounding P. calleryana, rather than a much needed practical one. For the record, the chances of you being allergic to Bradford Pears are slim to none because they aren’t wind pollinated. Bullied, bruised, blamed and constantly soaked in toxic agri-chemicals to try and kill it, the Callery pear is one of the most shamed species in the US. If you don’t believe me, look no further than the hundreds of online articles that alone focus on how the blooms smells like male ejaculate (that’s spermadine and putresine you’re smelling and it’s in a lot more plants than you think, including the beloved American chestnut).
Why didn’t Callery become the main rootstock of all pear production in the US? According to Reimer, on average, the tree isn’t very hardy (doesn’t like to grow colder than 7a, or below -10 fahrenheit), it doesn’t propagate all that well from stooling beds (primary means of producing rootstocks in the nursery industry), and has poor fruit qualilty. Why fruit quality matters for a rootstock is beyond me, but it was listed as a reason. In regions 7a and hotter, though, Callery pear is the best rootstock onto which one could graft European and Asian pear cultivars, but the research conducted on these pears was West coast centric and never really made it over to the East, even after Callery became a dreaded invasive.
Root Stock to Ornamental to Monster:
The Glenn Dale Maryland USDA research site had planted many P. calleryana seeds from Frank Meyer’s collection and by 1950, there were still a few P. calleryana trees remaining at the location. In 1952, researchers took notice of one particular thornless (many wild apples and pears have thorns) tree with an amazing white bloom (Callery produces fruit on lateral branches, on the previous year’s wood and on spurs of older wood. According to Reimer, It probably produces more blossoms than any other species of Pyrus). Thinking this could be of ornamental quality, cuttings were taken from this tree, grafted onto a seedling Callery pear rootstock, and planted in a subdivision nearby for testing. These trees were pruned/maintained, and after 8 years of oohs and ahhhs, they named the cultivar ‘Bradford,’ in honor of the horticulturalist who recognized its potential as an ornamental tree. By 1962, the Bradford Pear was available commercially and it became one of the most widely planted suburban trees in the US.
Around this time, other research stations and arboretums were noticing the ornamental value of the seeds planted from Meyer’s explorations. The National Arboretum produced, from a seedling selection, a cultivar called “White House,” and a seedling now known as “Autumn Blaze” was selected from the Horticultural Farm in Corvalis, Oregon.
The late 1960’s welcomed a gold-rush era of Callery pears, with many nurseries planting out seedlings from the original collections of Frank Meyer in order to find the next Bradford. This, friends, is where we start to transition from Amazing Rootstock to Amazing Ornamental Street Tree to “The Curse of the Bradford Pear.”
Pyrus calleryana is amazing for all of the reasons I listed above (insect and disease resistance, able to grow in a variety of soils and climates), but did you know it is also largely resistant to pest like deer, Japanese beetles, and wood boring beetles? The tree is precocious (often 3 years to fruit), the first to leaf out in the spring and the last to drop its leaves in the fall/winter. All of these qualities are noteworthy, yet have gone largely unnoticed due to one thing: The original ‘Bradford’ tree was self sterile.
When a tree is self-sterile, it cannot reproduce with itself in order to create progeny (fruit with viable seed). This wasn’t a problem when Bradford clones were planted out in the DC suburbs, because they were all genetically identical. When the bees would visit the flowers of one tree, and then the next, the pollen was sterile and did nothing to further fruit development. However, that was just one cultivar’s genes.
Remember when I said that Meyer walked 30+ miles a day? He covered so much ground while in China that he sent seed from Callery pear populations hundreds of miles apart. As it turns out, these populations produce genetically distinct cultivars under the species, and are totally able to cross with one another. Which they did once all those populations were brought together to intermingle in the US.
When the other ornamental selections like “White House” and “Autumn Blaze” showed up on the streets, the self-sterile Bradford pears soon became promiscuous in the neighborhood. By 1980, 300,000 Callery pear trees had been planted as street trees, producing huge amounts of small fruit with viable seed. From there, seedlings spread far and wide via birds and raccoons.
Today, in certain areas of the US, Callery pear seedlings can be found inhabiting fence-lines and ecologically stressed out pastures/roadsides, causing everyone to scream INVASIVE! THEY’RE INVASIVE! OMG KILL THEM. I CAN’T EVEN THINK STRAIGHT RIGHT NOW. EWWWW. IS THAT SPERM I SMELL? KILL.
But let’s take it out of all caps for a moment and go a bit deeper, because they deserve a chance.
Why is it so successful in the landscape?
Look, when you get into research about exotic plant species in the US, a huge majority of papers are biased in their research scope to focus on their invasiveness rather than what they offer. For instance, this paper (and there are many like this) decided to go ahead and only name one bird, the invasive European Starling, as being responsible for spreading callery pear in the landscape.
This is a type of fear mongering that I find over and over again. Rather than list the native birds that actually feed on Callery pear (there are MANY), research tends to dwell on the negative ones in order to further demonize this tree. I’ve been writing this paper for nearly 3 years (because 2 editions of this have been deleted on accident) and the only research I have been able to find listing native birds comes out of non-profit research and a masters thesis from Michigan, both BURIED in google. Over time and with much frustration given the extreme biases of US research, I decided to broaden my search for Callery pear dispersal in other countries, and the following is what I found out of Australia:
As you can see from the diagram above, the size of fruit directly corresponds with the number of frugivorous bird species that eat them. Like most ornamental fruit trees, Callery pear’s small fruit (8.5mm on average) is relished by birds, especially since they often have a tendency to hang on the tree well into winter- providing some much needed winter food for the birds that stick around.
Ok, so lets briefly put this all together: Ornamental= small fruit= bird food= birds poop= up comes Callery pear= produces thorns so not browsed= very tolerant of all the diseases= very tolerant of any soil type= it grows and thrives. But also, the Southeast is seriously just like China’s native range for Callery Pear (dark grey)…
I have two trains of thought that I’d like to go down: Fruit size and human impact on the land
1.) Fruit size: The average untamed fenceline in my climate contains autumn olive, barberry, multiflora rose, Callery pear, oriental bittersweet, honeysuckle, greenbriar, flowering dogwood, privet, american holly, hackberry, black cherry and a growing number of ailanthus. With exception to Ailanthus (which has a winged seed), what do all of these species have in common? They all produce fruits less than 15mm in size. Whenever there is a perch, such as a fenceline or a powerline, you’ll often see these species because they have small fruits that birds eat. The reason why we see so many Callery pear along these areas as well as in old fields and the built environment leads me towards the second thought…
2.) Human impact on land. Unlike many of the other species I mentioned in the paragraph above, Callery pear can thrive in compacted, low nutrient, poor draining soil with blazing sun and oppressive humidity. The reason why we see so much of it is because it thrives where humans have arrived and destroyed. Places like old fields, for example, which are are nutrient poor and compacted due to the robber-farmer that took more than the field could supply. Often in my area, those fields once supported tobacco and now are hayed by good-ole boy farmers in the area to keep the property in ag taxation for the owner, but no one ever puts any love/nutrition back into the land. What will grow in this scenario? Callery.
How can we make these pears less invasive?
Due to Callery’s fruit size attracting a high diversity of fruit eating birds, we can’t stop birds from eating the little pears and pooping in marginalized areas like fencelines and worn out pastures. To think we can kill enough Callery pear to make a difference is a lesson in futility because 1.) We live in the United States and you can’t go kill a neighbor’s tree in the name of INVASIVES if they don’t want you to and 2.) Each tree produces thousands of fruits. So, with that said, here are my top solutions to sustainably make Callery pear less invasive and more useful.
1.) Citizen Breeding. What makes Callery pear invasive is its ability to produce copious amounts of small fruits, which birds then eat and distribute all over the place. It seems logical, then, to want to try and breed larger fruits into our populations of Callery in order to stop the spread by birds. In order to reduce invasiveness by around 80%, all it takes is getting these trees to produce fruits that are around an inch (25mm) in diameter. Throughout the South and Southern New England, this is happening already in the “wild.” I’ve noticed trees that strongly look to be be hybrids of P. calleryana with P. communis (French) and/or P. pyrifolia (Asian). These trees have much larger fruits, usually golfball sized or larger and are often loaded with fruits dripping from the trees due to callery’s lateral bearing genetics (a possible phenotype identifier for callery hybrids). No research that I can find has evaluated the genetics of these larger fruited callery-like pears to see what exactly they are hybridized with, but I’m happy to help supply specimens if anyone out there takes an interest.
What is needed to hybridize these pears and get them larger? For starters, you’re going to need a collection of pears that bloom at the same time as Callery, which is quite early. Russian/Cold Climate and early Asian pears are likely your best bet for this, so I went through the GRIN database and have made a starter-list (there are a bunch more):
PI 541904- Seuri Li
PI 45845- Yaguang Li
PI 437051- Jubilee (cold hardy)
PI 541925- Kor 2
PI 267863- Pingo Li
PI 134606- Tioma (cold hardy)
PI 278727- La Providence
PI 278731- Sivaganga Estate
PI 307497- Seu Ri
PI 292377- Ranniaia Mleevskaia (cold hardy)
PI 541760- Chieh li x Japanese Golden Russet
PI 278729- Samy’s Estate
PI 541761- Chieh Li x Japanese Golden Russet 2
PI 541905- Szumi
PI 127715- Krylov (cold hardy)
PI 541326- Angelica Di Saonara
PI 324028- B-52 (cold hardy)
PI 541290- Mag 1 (cold hardy)
PI 132103- Shu Li
PI 312509- Tse Li
Appreciate this list? Help fund this type of work and more by purchasing charcuterie from www.hogtree.com.
You can request scions online from September 1 to February 1, of every year from GRIN. You can also probably buy many of these cultivars online. From there, I highly recommend you share scions of these for free every winter, as I plan to do, in order to help infuse larger fruiting genetics into Calleryana.
You might notice there are a bunch of Asian pears in that list and you might think: Eliza, those pears are super fireblight susceptible! And you are right, of course, but think of it this way: MANY trees that are listed as fireblight susceptible are actually quite tolerant to FB once they are established and reaching sexual maturity. With Callery being an amazingly fireblight tolerant rootstock, this should help to get your topworked trees past the first 2 years of heightened susceptibility so they can start to fruit. Once these Asian pears intermingle with Callery, there are two possible outcomes:
1.) The hybrid offspring are more fireblight tolerant than the grafted Asian pearent’s tolerance
2.) The hybrid offspring is less tolerant to fireblight than the grafted Asian parent’s tolerance and will probably succumb to the disease and die on its own.
Either are a win-win, really.
Next, you’re gonna need to go into your pear thicket and do some cutting and grafting. There are two scenarios I see often:
1.) Field full of Callery: If you have a thick field of calleryana, I would recommend getting a forestry mulcher in and cut/mulch rows into the existing Callery stand. Then, run the mulcher to cut out trees within the rows left standing so the remaining are at 15 foot spacings. Top the trees you’ve left behind above deer browse ( throw into the alley and run over those, too, with the mulcher) and graft on the early blooming large fruited cultivars.
2.) Fenceline/Border with Callery: This is the scenario We’ve been dealing with over the past few years along the farm fenceline. First thing I do is flag the trees I want to keep, which are at 15 foot spacings along the fence. Then we cut out and chip all the non-flagged callery trees using my neighbor’s chipper (I mulch my orchard with callery pear wood chips). While we are cutting out the non-flagged trees, I go ahead and also cut the tops out of the flagged trees. I pick a height that is above deer browse height and also has a lot of clear wood without branches, because that helps with grafting. In April (I’m in zone 7a), I make fresh cuts on the remaining pear trees and topwork all of them to fruiting cultivars. We’ve been doing this for 3 years and 2018’s topworked pears will be producing fruit this year.
This is totally doable and the result? An orchard of pears! You’d have to cut the tree down anyway if you were going to spray it, so why not turn it into a producing pear tree of value? My neighbors even pitched in to help us cut and chip in the name of supporting my vision and also getting rid of the fruiting portion of the Callery trees.
In 2-3 years, your top-worked pears will be flowering and that’s all part of your plan, as bees will mingle between surrounding Callery and the large-fruited cultivars you grafted. All of a sudden, your chances of getting larger fruit to come up from that fertilized seed will exponentially increase. And did I mention that you’ve also made yourself an orchard?
2.) Use them as rootstocks! Every Callery pear growing is automatically the best pear rootstock around. For all of you people out there who are inundated with deer pressure, graft to the Callery pears to any pear you’d like (or Winter Banana apple). Sure, you’ll get lots of leafy re-growth off the trunk for a couple years (which the deer or other livestock eat as tender shoots), but its also really easy to remove new growth with your hands (they pop off) or slightly older growth with pruners, and brand new shoots don’t have thorns. You’ll start to get fruit in 2-3 years.
One of the main reasons why Callery didn’t catch on as a rootstock, aside from root propagation failures and hardiness, is that they don’t produce dessert fruit (fruit meant for out of hand eating). This is the same reason why we’ve lost SO MANY fruit cultivars in the last 100 years. If you weren’t a dessert cultivar chosen by the cooperative extension to be grown in the early 20th century, you were phased out. However, in today’s markets, large fruited Callery pear hybrids really have a chance in fermentation, specifically cider blends and perry (cider made from pears). They are high in sugar (over 16% brix on average for the 200 or so hybridized trees I’ve evaluated), and run the gamut in acidity, tannins, aromatics and unusual characteristics. Since these trees are so disease and pest tolerant, which allows them to grow and produce copious amounts of fruit without the hand of humans or chemicals, they stand to produce the most sustainable fruits and alcohol in the South. We need more people working with them in order to make this happen because they aren’t apples and they need their own methods.