An unapologetic plant geek shares advice and opinions on gardening, the contrived and the natural landscape, as well as occasional topics from the other side of the gate.

March 22, 2009

Good Intentions - Bad Tree

Although they have never been on my A-list of trees, I must admit that the local display from the ornamental pear trees (Pyrus calleryana) has been remarkable this year. The flowers have been blooming now for close to three weeks and have managed to escape the blossom browning freezes that mar them in some years. They have also not been subjected to sustained spells of early heat that can cause the flowers to fall too early and the leaves to appear too soon. They are so stunning this year that you can't help but notice the sheer number of them that have been planted. From corporate office parks, to school yards, to street side plantings, to subsidised housing projects; ornamental pears trees are everywhere. With the exception of crape myrtle (Lagerstroemia), a local favorite - P. calleryana would be the most widely planted ornamental tree. Another thing made obvious by this year's display of blooms - just how many pears seem to have escaped the bounds of cultivation. There are more than a few places here where Pyrus is becoming the dominant tree species. While these wild stands are very pretty right now, the showy blossoms hide an ugly truth. When native ecosystems are altered by invasive species, plants and the animals that evolved with them are pushed out. The story of how this species has gotten to the point of invasiveness reminds me of Dr. Seuss's The Cat in the Hat Comes Back, where each effort to solve the problem of the pink cake stain only creates another pink problem.
Pyrus calleryana is native to China, Japan and Korea, and was brought to this country in the second decade of the 1900's. Researchers were hoping that its resistance to fire blight could benefit the edible European pear (Pyrus communis), which at the time was being decimated by the bacteria. Later in the 1950's it was noticed that this species could make a contribution to the horticultural as well as the agricultural world, and one particularly cultivar stood out - 'Bradford'. Like most P. calleryana, 'Bradford' exhibited disease and insect resistance, it flowered profusely starting at a young age, had a rapid growth rate, clean dark green foliage and had amazing late fall color. The overall shape of the tree was very tight and symmetrical and individual specimens showed a great degree of similarity with each other. It was also tolerant of pollution, heat, drought and the occasional flood. Hardy from zones 5 to 8, it was the perfect street, parking lot and residential tree for a good part of the nation. A landscape architect's dream come true, and if it never existed it would have to have been invented. They were planted everywhere by the tens of thousands.
There was one not so little problem with the perfect tree. As it aged those tight dense branches that grow at a very narrow angle were weak. Entire sections of the tree would collapse to the ground in wind and ice, ruining the shape which no pruning could ever restore. As this problem became apparent, fewer 'Bradford' were planted, but more of the varieties with a stronger branching structure were. 'Aristocrat' and 'Chanticleer' (aka 'Cleveland Select') became the pears of choice. When the streets were full of 'Bradford' pears there was little problem with them being invasive because they are self infertile. Now that these new varieties are being planted, often near older stands of 'Bradford' all of the cultivars are mingling with each other producing fertile fruit. These are being eaten and disseminated by birds, and now pears are coming up everywhere. These new pears seem particularly prone to growing in disturbed soil where most other vegetation has been removed. The same qualities that make the pear such a widely durable street tree, also make it uniquely suited to adapting to life outside of cultivation. As if all of this was not disturbing enough, now thorns are appearing on the trees after not being seen on the cultivated varieties. Perhaps this will provide more secure shelter for their friends the birds and possibly keep the deer and the groundskeepers away.
Should anything be done with species, like the ornamental pear or the Canada goose whose DNA makes it possible for them to thrive in the ecological opportunities humans (perhaps nature's most adaptable species) have inadvertently created for them?

For more detailed, scholarly information about Pyrus calleryana and its invasiveness you can read:
The Beginning of a New Invasive Plant
by Theresa M. Culley and Nicole A. Hardiman
On the Spread and Current Distribution of Pyrus calleryana in the United States
by Michael A. Vincent

For different perspectives on different trees you can visit:
Festival of the Trees - a monthly blog carnival for all things arboreal, which will be hosted next month at The Marvelous in Nature.


  1. I agree Les, they are beautiful this year; however, I do believe that there’re 'overused'.

    Very interesting post!

  2. Great analogy with the Cat in the Hat Les. I had no idea that the different pears were cross pollinating and putting out fruit. Oh what a tangled web...
    It is amazing to see how many pear are planted in this area.

  3. Wow! Eye-popping gorgeous! Three weeks? I think I saw a crocus shoot today. These trees are popular in NYC for those reasons. Too much of a good thing. We have issues with invasive in Maine too.

  4. *sigh* thanks for the information. When will we ever learn?

  5. Hi Les, this problem gets worse every year. The general public sees the pretty blooms, sees the trees for sale cheaply everywhere, even at the grocery! and plants them by the tens and more. The word about the invasiveness and general flaws in the trunk structure have not reached them even though gardeners like us have known for years. I am finding more and more seedlings in my own garden, even though we have none of these, for they are everywhere and being planted daily by the unsuspecting. It will get worse before it gets better, like some other things that could be mentioned here. :-)

  6. Informative post Les. I think they are overplanted in our area like the Crepe Myrtle. But I prefer the latter myself.

  7. Nothing we can do about nature sharing pollen is there? They are becoming less popular in our area and the Crape/Crepe Myrlte is taking over. We always want sometimg blooming don't we?

  8. I would say well that's just peachy, except, um, it isn't, on two counts! :) (Man, I hope that makes sense.)

  9. I stopped at my favorite nursery a few weeks ago. I asked one of the associates if they had recently fertilized everything..she said.."No, that is the smell of a thousand Bradford Pears in bloom!" They stink. As I looked outside the grounds I saw them everywhere in the suburban landscape. I see them at the edges of our parks and on the interstate. One question: Which invasive will win...the Bush Honeysuckle or the Bradford Pear..both horribly destructive to the ecosystem! Les an excellent post, I wish you hadn't had to write it! gail

  10. I knew they were overplanted, but had no idea about the invasiveness of the species. They are beautiful this year, but their ubiquity means I don't ever have to own one.

  11. Alan,
    Overused is one of the reasons I did not like them even before I knew about their invasiveness.

    All of that reading.

    Phillip M.,
    Sorry you had to look at them.

    Maybe they would be OK in highly urbanized areas like NYC where they would be less like to encounter wild areas inwhich to grow.

    Kim D.,
    My guess would be "too late".

    Maybe you could dig up your seedlings and sell them at the end of the driveway to unsuspecting passers-by.

    I am not sure that I could see too many Crapes.

    Yes it probably is too late, the pollen has left the pistol.

    Perfect sense to me.

    The polite description of the smell is that of shrimp gone bad. We are fortunate that we do not have a bush honeysuckle problem here.

    With their numbers, no one has to have one in their own yards. There are plenty around for everyone.


  12. Another fun post. My last place here in Lincoln had a lovely pear-lined avenue leading up to it. Gorgeous in spring. Then it got stormy in June and July as it always does, and the streets became impassable with large fallen limbs. I planted a 'Cleveland Select' there at my old place that I got for $5 at Home Depot, and it took nicely. Then I felt bad about it as I started to garden more, and planted a serviceberry nearby. I'll have to drive by soon and see how they're doing.

  13. Lagerstroemia has special memories for me, because I was born and educated in India, where they were very common.

    Lovely shots.

  14. Great essay!

    In Boston, I had experience with the following: "There was one not so little problem with the perfect tree. As it aged those tight dense branches that grow at a very narrow angle were weak. Entire sections of the tree would collapse to the ground in wind and ice, ruining the shape which no pruning could ever restore. As this problem became apparent, fewer 'Bradford' were planted..."

    I was in San Mateo for the SF Garden Show and the Callery pear seems to be a favorite street and park tree.

  15. Very informative post. Beautiful pictures. Congrats on the POTD Award from authorblog.

  16. Benjamin,
    Service Berries are a great native and are often listed as a subsitute for pear-shy gardeners. At least the fruit is edible and the flowers don't smell like last week's shrimp.

    Thanks for stopping by and thanks for listing me on your blog as a Post of the Day. Crape Myrtles are one of my favorite trees and are used everywhere here. Look at my Bloom Day post from July 08 if you want to see my ode to them.

    Thanks for the compliments, thanks for the heads up on POTD and thanks for stopping by - you are welcome back anytime.


  17. Georgia,
    They probably don't have to worry about ice storms taking them out in San Mateo, but I don't know about the wind. Stormy weather is what usually destroys Bradford's here, not so much ice. We seem to be just a little south of the major ice storms.


  18. I am not sure that Bradford pears were used much in Canada, so I can admire the beauty, and leave all the problems to the Americans.
    I love the photos, though. My favourite is the cluster of flowers in a puddle!!

  19. Great post, Les. Bradford pears are just common enough in Calif. for me to be aware of them, but not so common that I can recognize them most of the year. The city offered us a Bradford pear as one of six choices for a street tree; but we decided to forgo the street tree altogether.

    The bit about the thorns was esp. interesting!

  20. They're not one of my favorites either!

  21. Really interesting post. I had never thought about them cross-pollinating (for some odd reason I thought they were sterile) - but that makes alot of sense. I've never really liked them - but then, they do terribly here in storms - but even so, they are over-planted.

    It was funny - a week or so ago a friend from near Louisville called me and told me that she thought something had died in her backyard. I kept asking her about plants, and then she said that she had a Bradford pear in full bloom in the backyard - she didn't know how terribly they smelled!