Why do ginkgo trees drop all their leaves at once?

Most trees drop their leaves over a few weeks. A ginkgo can go from a full crown of gold to bare branches in a day or two, leaving a bright yellow carpet underneath.

All at once

Ginkgo is one of the last trees to color, and when it does, the whole tree turns an even butter-yellow. Then, often right after the first hard freeze, it drops most of its leaves within a few days, sometimes almost overnight.

Why it happens

Like other trees, ginkgo cuts its leaves loose by forming a layer of cells at the base of each leaf stem. On a ginkgo, those layers seem to form across the whole tree at nearly the same time, so the leaves are all ready to fall together, and a hard frost is often what finishes the job. Many ginkgo leaves also grow in clusters on short, stubby spurs, so a single frost affects a lot of them at once.

Scientists haven’t pinned down every detail of why ginkgo is so much more synchronized than most trees, but the result is easy to see on any city street lined with them.

A very old tree

Ginkgo’s family goes back more than 200 million years, and it’s the only surviving species in its group, which is why it’s often called a living fossil. It’s rare in the wild, and nearly every ginkgo in the U.S. was planted.

It’s also famously tough. Ginkgos handle pollution, salt, and cramped soil well, which is why cities like them. In Hiroshima, several ginkgo trees near the center of the 1945 atomic blast survived and are still alive.

Why cities plant male trees

Female ginkgos drop fleshy seeds in fall that smell like rancid butter when they’re crushed on the sidewalk, so most planted street trees are males.