Spring is here: Watch out for leftover Ginkgo “stink bombs”

Ginkgo Tree Fruit contains butyric acid, which is a chemical also found in vomit.

Ginkgo Tree Fruit contains butyric acid, which is a chemical also found in vomit.

By Kayah Gausman, NewsNetNebraska

They’ve been called ‘vomit trees,’ dropping seeds referred to as ‘poo berries’ and ‘stink bombs.’ They emit an odor commonly described as smelling like sour milk, old cheese, rancid butter, and dog poop.

And with warmer weather melting away the snow and spring rains making mud, a familiar smell is back in downtown Lincoln.

It’s the Ginkgo Tree, one of the most commonly used trees in cityscapes across the United States.

Their beautiful fall color and ability to thrive in urban areas makes them a popular choice in cities across the country. Most cities pick the non-flowering male trees for landscaping to prevent the smelly fruits from stinking up the sidewalks.

And, indeed, those male trees were planted here. But something happened between planting and now: They changed genders.

“If some trees are under stress, like the drought last year, or like being inside an urban area with the pollution and everything, the males shift and develop female ovaries and switch sexes to ensure their survival,” George Pinkerton, director of maintenance for the Downtown Lincoln Association said. “It was never the intention to plant female trees down there.”

This gender shift is a pretty rare phenomenon.

It’s more common in trees that are grafted, or bred specifically, for urban environments. The trees are developed and bred with specific Ginkgos that are especially resistant to disease or have a significantly rich color to the preference of the landscape designer. When the trees are grafted, then placed in close quarters, they can take to the qualities of the tree that bred them, and those trees are usually female.

“It’s a really interesting thing,” Kim Todd, extension landscape specialist at UNL said. “It’s called a graft union, and it’s common in downtown street trees, but drought can cause the switch, too.”

Even though the trees have the potential to develop into smelly, bomb-dropping menaces in the early fall, Todd says they’re a good choice for cities regardless.

“They’re pretty disease and pest resistant, and in a city you can’t afford to spend a lot on chemical control, nor should you spend a lot for chemical control. They’re a smart choice,” Todd said.

Just because they’re a smart choice doesn’t mean city residents are happy about them, however.

“I think we’ve tried to get them cut down. We’re even in the process of building a whole new church but we still have to protect them throughout the entire construction process and they still won’t let us cut them down,” Henry Mattern, head janitor at UNL’s Newman Center said.

The Newman Center has several Ginkgos lining the sidewalks leading to their front door, and the staff isn’t happy about the smell they cause as people come and go.

“Whenever they drop their berries they get all over the sidewalks and it gets all over the congregation’s shoes and they track into the church and it smells. We still clean the church as often as we would anyway, but it smells worse when we do it.”

The grounds crew at UNL and the Downtown Lincoln Association does their best to maintain them and keep the seeds off of the sidewalk, but there’s only so much they can do.

“Once they start dropping the fruit, it becomes a daily task to make sure we rake it up or pick it up,” Jeff Culbertson, East Campus landscape manager at UNL, said. “In places where they use them as street trees, if they’re not careful with their selection or if somehow the female trees have been mixed in, then it becomes a bigger issue.”

In between clean-ups — and with warmer weather making a walk in the grass more tempting — it’s not a bad idea to walk around the berries. Mattern said the janitorial staff appreciates people dodging the smelly landmines.

“We always notice them,” he said. “It’s always easy to tell when the poo berries are falling.”

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