That unmistakable spring smell most often comes from the Bradford pear, a white-flowering tree planted along streets and in yards across much of the United States.1Reno Gazette Journal. Reno’s stinkiest tree, the Bradford pear, is blooming again. Why do they smell so bad? The flowers release some of the same kinds of nitrogen compounds that give semen its smell.2Reno Gazette Journal. Reno’s stinkiest tree, the Bradford pear, is blooming again. Why do they smell so bad? The odor does a job for the tree, and the tree has also become unwelcome for reasons that go well beyond how it smells.
How to Recognize a Bradford Pear
Bradford is one variety of the Callery pear, a tree from Asia with the scientific name Pyrus calleryana.3Reno Gazette Journal. Reno’s stinkiest tree, the Bradford pear, is blooming again. Why do they smell so bad? It was tested as a street tree in Maryland in the 1950s and sold commercially from around 1961.4Arnoldia. The Rise and Fall of the Ornamental Callery Pear Tree People liked its fast growth, its abundant early-spring flowers, its leaves that stayed into late fall, and its toughness.5Arnoldia. The Rise and Fall of the Ornamental Callery Pear Tree So it was planted widely in neighborhoods across the eastern United States.6Arnoldia. The Rise and Fall of the Ornamental Callery Pear Tree If you smelled it near homes, offices or parking lots, a planted Callery pear is the likeliest culprit.
In early spring the whole crown turns white with dense flower clusters, often before or just as the leaves appear. The shape is a tidy oval or teardrop, and the leaves are glossy and turn red or purple in late fall. It rarely produces anything like an edible pear, only tiny hard fruits about the size of a pea.
You may hear other names. Bradford is the best known, but nurseries sold many look-alike varieties, including Chanticleer, Cleveland Select, Autumn Blaze and Aristocrat. All of them smell similar in bloom, and people often call any of them a “Bradford pear” casually.
White flowers alone don’t settle it, since cherries, crabapples, serviceberries and dogwoods also bloom white in early spring. Callery pear flowers sit in tight rounded clusters along the twigs, and each flower has five rounded white petals with dark reddish anthers in the center that look like tiny dots. Ornamental cherries tend to have pink or white flowers hanging on longer stalks, and many have a more spreading, vase-like shape than the pear’s tidy oval. The strong smell is one more clue, since many common white-flowering street trees smell sweet or faint up close.
When you catch the smell, look up for a tree solidly covered in small white flowers, and notice whether identical trees are lined up along the street or lot. Step close to a cluster, because the smell is strongest right at the blossoms. It should also coincide with peak bloom in early spring.
Why the Flowers Smell Like Semen
Semen’s characteristic odor comes largely from a compound called spermine, which smells fishy.7Wikipedia. Spermine Compounds named spermidine and spermine have been found in Bradford pear flowers.8Reno Gazette Journal. Reno’s stinkiest tree, the Bradford pear, is blooming again. Why do they smell so bad? Another compound, 1-pyrroline, is known to smell like semen to people and is a likely cause of the pear blossom odor.9eScholarship. A Potential Mechanism for Sensory Perception of Unpleasant Floral Scent of Pear Blossoms
The match can be remarkably close. In one semen-smelling flower, 1-pyrroline made up almost 60% of the scent.10eScholarship, University of California. A POTENTIAL MECHANISM FOR SENSORY PERCEPTION OF UNPLEASANT FLORAL SCENT OF PEAR BLOSSOMS When people sniffed that blossom alongside the lab-made scent, they couldn’t tell them apart.11eScholarship, University of California. A POTENTIAL MECHANISM FOR SENSORY PERCEPTION OF UNPLEASANT FLORAL SCENT OF PEAR BLOSSOMS
Plenty of people don’t say semen at all. Many describe the smell as rotting fish, garbage or bodily fluids.12Reno Gazette Journal. Reno’s stinkiest tree, the Bradford pear, is blooming again. Why do they smell so bad? That makes sense, because these nitrogen compounds, called amines, also drive the smell of decaying fish and flesh. Humans even have a smell receptor that reacts strongly to trimethylamine, a classic fishy amine.13PubMed Central. Human Trace Amine-Associated Receptor TAAR5 Can Be Activated by Trimethylamine Some tree-service sites blame trimethylamine for the pear smell, but the evidence on pear blossoms doesn’t confirm that. The better-supported chemistry points to 1-pyrroline and spermine-type compounds, and the exact mix is likely several amines together, with the fishy note coming from more than one of them.
Warm days make it worse. Scent compounds evaporate faster as temperatures rise, and a sunny, still afternoon concentrates the smell around the tree. On a cool or windy day the same tree can be barely noticeable.
People also notice it very differently. Smell sensitivity varies, and blocking one receptor has been shown to raise how much fishy amine is needed to notice it. Some people find the smell overwhelming while a companion smells little.
Other Trees and Plants With the Same Smell
Chestnut flowers give off a semen-like odor from four nitrogen compounds, including 1-pyrroline.14PubMed. Molecular analysis of semen-like odor emitted by chestnut flowers using neutral desorption extractive atmospheric pressure chemical ionization mass spectrometry The same compounds appear in photinia, a hedge shrub, and in a related Asian tree, Castanopsis.15PubMed. Molecular analysis of semen-like odor emitted by chestnut flowers using neutral desorption extractive atmospheric pressure chemical ionization mass spectrometry
Bloom timing and flower shape help narrow it down. Early-spring white clusters on a mid-sized tree point to Callery pear. Chestnut blooms later, in early summer, with long creamy catkins rather than white clusters, so a semen-like smell in June or July points away from a Callery pear. A clipped hedge with flat white flower heads in spring suggests photinia.
Chestnuts are more often found in parks, older estates, orchards and woodland edges, and they grow into large, broad trees.
Photinia is usually planted as a clipped hedge or screen, so the smell can seem to come from a wall of green rather than a tree. Its spring flowers are small and white and gathered into flat-topped clusters, and many varieties also have bright red new leaves. Hedges are often trimmed before they flower, so a hedge that blooms only in some years may smell only in those years.
Why a Tree Would Want to Smell Like This
The odor evolved to attract a particular kind of pollinating insect.16Reno Gazette Journal. Reno’s stinkiest tree, the Bradford pear, is blooming again. Why do they smell so bad? Bradford pear flowers draw flies rather than bees.17ABC4 Utah. What Tree Smells Like Semen? The Science Explained Flies seek out decaying matter, and amine smells signal food or egg-laying sites to them.
Other plants also evolved stench to lure such insects.18The Scientist. Floral Stink Evolved Through Three Amino Acid Changes In wild ginger, changes in just three building blocks of one protein turned it into a factory for sulfur stink compounds.19The Scientist. Floral Stink Evolved Through Three Amino Acid Changes
Early spring suits this strategy. It’s cold, and bees are often fewer or less active, so flowers that rely on bees alone can go unpollinated. Flies are active in cooler weather than many people expect, which gives a fly-attracting tree a pollination option when bees are scarce. Flowering early also means little competition from other blooms for those insects.
Is the Smell Harmful
The smell is released during blooming, especially in warm weather.20Blackhawk Tree Services. Why Do Bradford Pear Trees Smell So Bad? | Blackhawk Tree Services It fades within a couple of weeks as the petals drop.
A strong smell isn’t the same as a toxic one. The nose is extremely sensitive to amines, so people can smell them at very low concentrations, far below levels that would be a health concern.
Some people feel queasy or get a headache from a strong smell, and that reaction comes from the smell being unpleasant, not from poisoning. Sneezing, itchy eyes and congestion in spring are more likely to come from pollen, which may be from the pear or from other trees blooming at the same time. Pear pollen is carried mainly by insects rather than wind, so it’s less likely than wind-pollinated trees like oak or birch to cause hay fever, though this can vary by person.
To live with it, close windows on the side facing the tree on warm afternoons. Sweeping up petals that drop on cars and walkways can help, and the smell ends when blooming does.
Fallen petals aren’t known as a poison for dogs, cats or children, though eating a lot of any plant material can upset the stomach. The tiny hard fruits drop in fall; swallowing a few isn’t a typical concern, but it’s reasonable to discourage pets from eating them, since pear seeds contain compounds that can release cyanide. If a pet is eating large amounts of plant material and vomiting, call a vet.
Why Bradford Pears Are Falling Out of Favor
The tree is now known for branches that snap, which drove it out of favor as a street tree.21Arboriculture & Urban Forestry. Branch Strength of Bradford Pear ( Pyrus calleryanavar. ‘Bradford’) Bradford pears tend to grow many upright branches that attach to the trunk at narrow angles, and narrow joints trap bark between the branches and make weak attachments. The tree also grows fast, so its limbs get heavy before the wood has become strong. Storms and heavy ice often split older Bradford pears.
When it was introduced, Bradford could not pollinate itself, so it made no viable seeds.22NC State Extension Publications. Callery Pear: Bradford Pear, Other Varieties, and Their Invasive Offspring The idea was that a street lined with only Bradfords would not spread. But as more Callery varieties were planted, they cross-pollinated and produced fertile seeds.23NC State Extension Publications. Callery Pear: Bradford Pear, Other Varieties, and Their Invasive Offspring Shoots growing from its rootstock can cross-pollinate too.24N.C. Tree Farm Program, Inc.. Callery/Bradford Pear The seeds sit in small fruits that birds eat, and birds and other animals spread thousands of seeds well beyond where the trees were planted.25KSMU Radio. Bradford Pear Trees: An Invasive Species Wild Callery pears now take over fields and forests, shading out native plants.26N.C. Tree Farm Program, Inc.. Callery/Bradford Pear
You can spot these escapees in early spring, when thickets of white-blooming trees in fields or along roadsides stand out before other trees leaf out. Wild ones often have sharp thorns, which planted Bradfords usually lack.
South Carolina listed Callery pear as a state plant pest in 2021.27USA Today. Bradford pear trees are banned in a few states. More are looking to replace, eradicate them. Selling Callery pears, including Bradford, became illegal there from October 1, 2024.28FOX Carolina. Program exchanges Bradford pear for native trees Some programs let owners trade a Bradford pear for a native tree.29FOX Carolina. Program exchanges Bradford pear for native trees
If one grows in your yard, check with your state extension office about local rules and trade-in programs. A native flowering tree such as serviceberry or redbud makes a good replacement. Cut sprouts from the base, since rootstock shoots can flower and cross-pollinate. If large limbs overhang a house or car, hire an arborist.