The arrival of spring often brings the pleasant scent of blooming flowers, but for many people, the season is also marked by a distinctly foul odor. This pervasive smell, frequently described as ammonia-like or resembling cat urine, can be strong enough to raise questions about neighborhood sanitation. The phenomenon is not caused by local animals but by a common ornamental tree. This article will identify the source of this springtime stench and explain the biological reason behind it.
The Callery Pear: Source of the Odor
The primary source of this springtime stench is the Callery Pear, scientifically known as Pyrus calleryana. This species, particularly the widely planted cultivar ‘Bradford Pear,’ was introduced to North America as a fast-growing, aesthetically pleasing ornamental tree. Its popularity stems from its compact shape and its spectacular display of abundant white flowers that appear very early in the spring. These dense clusters of five-petaled white flowers produce the offensive smell.
The Callery Pear became a staple in urban and suburban landscapes due to its adaptability and consistent fall color. Despite its initial appeal, the tree is now considered a problematic invasive species in many regions, escaping cultivation to colonize natural areas. Its weak, narrow branching structure also makes it prone to splitting apart in high winds or ice storms, creating a maintenance hazard. The tree’s widespread use means the unpleasant odor is a common experience across many neighborhoods during its short bloom period.
The Biology Behind the Bad Smell
The distinctive, foul odor released by the Callery Pear flowers is a result of specific volatile organic compounds (VOCs) the plant produces. Scientists have identified the primary culprits as amines, which are nitrogen-containing compounds. These chemicals, specifically putrescine and cadaverine, are byproducts of decomposing proteins.
These compounds are the reason the smell is often compared to rotting fish or decaying flesh, as they are commonly associated with organic decay. The tree uses this powerful scent as a biological strategy to attract specific pollinators, generally flies and other insects that seek out decomposing material. This scent is a highly effective way to ensure reproductive success during the cool, early spring when traditional bee pollinators may not be as active.
Are There Other Smelly Plants?
While the Callery Pear is the most notorious offender among trees, other plants can emit similar unpleasant odors. Certain shrubs, such as English Boxwood (Buxus sempervirens), are frequently noted for giving off a scent that can resemble cat urine, especially when the foliage is wet. This odor generally comes from the leaves rather than the flowers and is usually less intense than the pear tree’s springtime bloom.
The flowers of some Hawthorn species (Crataegus) also produce an odor that is often likened to rotting material. Other garden plants, including some varieties of Shasta Daisy (Leucanthemum × superbum) and Yellow Alyssum, can also emit a strong, ammonia-like scent. These examples show that a variety of plants use strong chemical signals to interact with their environment and attract necessary insects.
What To Do About a Stinky Tree
If a Callery Pear is the source of the odor in your yard, the first step is positive identification beyond the smell. Look for a tree that is one of the first to flower in early spring, displays a tight, upright, or conical shape, and has small, hard, inedible fruits in the fall. The leaves are oval-shaped with a finely toothed margin and have a glossy, dark green appearance in summer.
Given the tree’s invasive nature and structural weaknesses, many experts recommend removal and replacement with a native species. Small saplings can often be pulled by hand, but mature trees require cutting and treating the stump with an herbicide to prevent regrowth. This ensures the tree will not continue to spread its seeds into natural ecosystems.
Excellent native alternatives that offer similar ornamental features without the smell include Serviceberry (Amelanchier spp.), which has beautiful white flowers and edible fruit that benefits local wildlife. Eastern Redbud (Cercis canadensis) provides vibrant pink-purple flowers early in the season, and American Fringetree (Chionanthus virginicus) offers delicate white blooms with a pleasant, subtle scent. Replacing the Callery Pear helps restore ecological balance while eliminating the offensive odor.