What are those stinky trees?

pear tree blossoms

Pretty. Stinky.

By Ryan Palumbo

I was recently reduced to a position not unlike one commonly assumed by a heaving cat while on my way up from University Heights to B'yond Style for my monthly haircut, as I passed by a row of trees sporting what anybody would surely consider to be a beautiful arrangement of white flowers from each branch. Curious.

The next day, while riding the #10 CDTA bus, I smelled it yet again. Unsurprisingly, those trees were around. At that I concluded that the miasma that had been violating my olfactory system for nearly a week had to be radiating from these trees.

I am sure many, if not all of you, have seen these trees as the warm weather gives way to the blooming of flowers and leaves, and have no doubt noticed that they STINK. And not only do they just stink: they seem to give off what some have called a particular, familiar odor ("fish that's been sitting out way too long" is another description).

Thus my research into these odorous organisms began.

The scientific name for the trees is Pyrus calleryana -- that is, they're pear trees. The variety is native to China and Taiwan, and was brought to the United States in the early 1900's to be used in hybridization experiments to produce a more fire-resistant pear tree; this proved unsuccessful. However, in the 1950s it emerged as an alternative ornamental tree, and was utilized extensively in landscaping due to its innate resistance to cold, disease, drought, fireblight, and pollution (it's been described as a "near-ideal street-tree"). However, the trees do have one weakness -- they tend to damage easily in strong wind. (I say: bring on the thunderstorms!) There are now a bunch of cultivars, the Bradford one of the most popular.

The Callery pear, as the trees are commonly known, is characterized in the springtime by clusters of white flowers at the tips of their branches that develop in March. Pretty. And stinky.

Which brings us finally to this: why does this tree smell so horrible? As far as I can tell, there isn't any research on why exactly the trees stink. However, I did come up with this: all of the approximately 30 species of pear contain the aroma compound pentyl butanoate. I will spare you the biochemistry -- this is the compound that makes pears and apricots smell as they do. One the precursors of pentyl butanoate is butyric acid, which is present in butter, parmesan cheese and... vomit.

But it appears that nobody has investigated the exact origins of P. calleryana's scent. And I don't blame anybody for not trying.


Glad someone is finally talking about these trees - people have seriously thought I was crazy when I brought up the subject. So many of them around campus.

Thank you for clarifying that! I too have heaved like a cat at the smell of those trees. They are AWFUL!!! pretty to look at but so stinky.

Thanks for the explanation, Ryan! I have been trying to place my finger on the smell for quite some time. Earlier in the spring I thought the trees smelled like cement being mixed. Glad I've yet to experience the vomit-scented blooms.

Maybe it's my imagination, but they seem to stink much worse this year. It's much more noticeable. I wonder if it's the same phenomenon that is also bringing us a much worse allergy season than usual.

and you didn't even mention the berries that the trees produce all winter long. those are almost as enjoyable as the lovely scent in spring.

My son practices baseball at Frear Park in Troy where you can find some of these trees. They smell like many cats sprayed right on them. We noticed the smell coming from the trees and then the next day we pulled up in the car to park for practice again and my son says "Don't park here, please move the car, I can't get out of the car next to those awful smelling trees." We moved the car.

Ha! I've got one of those trees and maybe I've been blaming my kids' feet for the smell, when really it belonged to the tree. I wonder if the smell has anything to do with the fact that birds eat the winter fruit and then barf it up (all over my car if I pull in too far). I will say, I'll put up with the nuisance to see the gorgeous, deep red cardinals perched there on dreary January days. Live free, pear tree!!

Yeah, I've noticed a strong scent of cat pee near the trees, but not so much vomit. I seriously thought that all the toms in the hood were using it as their sprayground (the corner of Dove and Jay).

Nice find. I knew something had to be up when yesterday morning on Twitter at least three people noted that Albany smelled horrible.

I likened the smell to old fryer grease! Glad I'm not the only one wondering about these. They line many of the streets in Saratoga too.

Those trees were horrible this season! I've noticed them smelling in previous years but never as bad as this. They smell a little like bleach mixed with pee to me.. and the worst area for them is definitely on 15th street in RPIs campus. They have some spectacularly large and stinky trees along there.

Excellent post that spoke to my soul. (Haha.) I have noted a smell that is pretty spot-on, but also (due to it's controversial, and anatomical origins) gross and inappropriate.

May the wind blow and the blossoms disperse.

Are you sure that the Callery Pears are the source of the annoying stink? We had a very large one in front of our house in NYC for many years, and I never noticed any smell (good, bad, or otherwise).

When I have smelled stinky trees they are usually Ginkgos

I wonder if the smell of Callery Pears is something that only some individuals notice, or if there is something specific that causes the smell which might not always occur (e.g. (unfertizlied?) blossoms that have fallen to the ground and not been swept up). Or perhaps it is that only the male (or only the female) pear trees that have the bad smell?

@alex dupuy

i would say that pyrus calleryana is absolutely the source of the stink. therefore i ask--are you sure it was a callery pear outside of your home?

if you notice, the leaves of the ginko are kind of trapezoidal, whereas the leaves of the callery pear are more elongated. take a look at any of these stinky trees (hard to discern now that most have leafed out, but ive noticed those in guilderland have for the most part retained their flowers as of sunday) and you'll notice that they too have long leaves (although i cannot rule out that there are ginkos as well as callery pears planted in albany--im sure there are, but research lead me more strongly towards concluding that this "particular" stink emanated from callery pears. that and i didnt necessarily examine the leaves of EVERY tree that ive walked by, but i certainly more or less noticed the elongated leaves upon leafing out).

also. any odorant becomes more obvious as the concentration increases. this spring in particular, the temperature at which the flowers bloom occurred far earlier than the temperature at which the trees leaf out (i.e. we had a warm, early, and therefore long spring). thus, the number of trees in any given location that were able to bloom flowers and stay at a state poised but preceding leafing out was greater than if it started to get warm in late april, say (i.e. blooming would occur shortly before leafing out, preventing the establishment of a substantially long flower-only state and thus one could assume that the smell would not be as strong). therefore, the particular intensity of the stink this year over others (as reported by commenters above) supports that.

the other alternative--of course--is that some people can smell it and others cant (such as with other odorants; i cannot name any off of the top of my head, though i know there are some things that some people can smell that others cant, or are at least less sensitive to). another alternative is that some people do simply have different capacities to smell (e.g. smokers have decreased olfaction, as well as the elderly, or people with certain neurodegenerative diseases, etc.).

your other suggestions are not as strong. i have noticed that the fallen blossoms smell less (i.e. theyre dead) and are not metabolizing such compounds as butyric acid to pentyl butanoate--what i hypothesize may contribute to its awful smell. that and upon death, these odorants will be naturally turned over as cell maintenance ceases, and are broken down by bacteria, etc. thus their chemical properties attributable to scent will change.

and also, pyrus calleryana flowers are--like most flowers--hermaphroditic, and thus different genders cannot be attributable to differences in scent.

interesting ideas every one of them, though! any chemical botanists out there may want to jump on this!

sure glad i lost my sense of smell in the great mold infestation of 19-aught-8.

Not sure if these trees are the same as the Ginko trees where one is male and the other is female and on or the other (not sure which) produces the fruit which means if you have the one that doesn't stink then you have the one that does not produce the fruit. Also, you need to have both to produce fruits or in this case the stink.

Ugh! We have a Crusader Hawthorne here in our backyard in CO that has noticeably gotten worse each year. And every year I forget and go in search of the smell. And find it. In my beautiful white blossoms that should smell pretty if they're going to look pretty! Seriously considering chopping it down.

My son and I have called these "Poo Poo Trees" for years because we happen to think they smell like dog excretions... it is nice to know that it isn't just because dogs like to use the bathroom around them so much that they smell so horrible.

It is July in Texas and close to 100 degrees. These horrible smelling trees are in bloom right now. I wonder if only certain lucky people can smell them. People look at me as if I've lost it when I mention stinky trees

LOL. I have those stinky trees in Southern Maryland as well. I hold my breath whenever I have to pass one. Smells like bleach and urine moxed. It's disgusting. At first I thought it was some crazy cat lady house, then I thought possible meth lab. Glad to see it's a tree, but still wish they weren't here.

There are many of these trees lining the sidewalks at Discovery Elementary School in Boise, Idaho, and man do they stink? The kids say the smell is like a dirty diaper but the I'm more inclined to cat whiz!

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