Ginkgo trees can be stunning in fall. The broad, fan-shaped ginkgo leaves turn a brilliant yellow that is particularly striking at sunrise and sunset. Then, the leaves all drop quickly -- sometimes in one day -- and the show is over. Something different is happening this year -- the leaves are dropping and many are still green.
Why No Fall Color?
The short answer likely is that we had warm weather through September, then a lot of cold and wet weather in October, followed by a freeze and high winds. To the leaves, it seemed like summer suddenly went to late fall. We're shutting down. No time to change color!
Of course, there is a lot more science behind this and not all ginkgos have remained green. I found a bright yellow tree on my walk yesterday, though many more have seemed greener than normal.
Here's the long explanation:
When days get shorter and weather cools in fall, plants prepare for winter by shutting off supplies of chlorophyll to their leaves. Chlorophyll is the main substance that gathers light and turns it into nutrients. It also gives plants their green hue. But chlorophyll is not the only substance in leaves. These background substances include xanthophyll, a pigment that makes things yellow, such as egg yolks and the leaves of ginkgo trees in fall.
After a freeze, the leaf stems develop a scar-like tissue where they connect to branches. Once the scar is formed, they drop. Ginkgos are among the trees that develop the scar all at once, which is why their leaves tend to drop so quickly. Other trees, such as maples, develop these scars slowly and their leaves tend to drop over a couple of weeks or more.
The Unusual Ginkgo
Ginkgos are a popular tree in urban yards because they handle salt well and have few pests or diseases. They are pretty, too, with their fan-shaped leaves, and they can grow to 80 feet tall. They are an unusual tree in that they are classified as a conifer, along with firs, spruces and other evergreens. Ginkgos have been around 150 million years, and the Ginkgo biloba is the only species in the genus.
The ginkgos people plant today came from China, and that is the one concern about ginkgos as an urban tree. Because they are nonnative, they are not popular with our native pollinators.
Have your ginkgos turned yellow this year?