I'm used to ginkgo trees turning yellow and then suddenly all losing their leaves all at once. This fall, however, we had a sudden temperature drop and snow and then, whoosh, the leaves started dropping while they were still green.
I knew ginkgos did this but I'm kind of ashamed to admit I never looked up why they do it until this minute. It's because (according to a writer from the Chicago Botanic Garden, via the Chicago Tribune):
The stems of leaves on deciduous trees are known as petioles. Before leaves drop in the fall, these petioles produce a protective layer of cells that work like a scar to protect trees from diseases entering the exposed tissue. [A] maple tree produces these protective scars over several weeks as the amount of daylight and temperatures decrease, and they begin forming on the most exposed leaves, which is usually top.
As leaves drop and expose interior leaves to colder temperatures, these interior leaves form new protective layers, and additional leaves drop. Eventually, a hard frost causes all the remaining petioles to form this protective layer and all remaining leaves fall. For maples and many other trees, this process can take several weeks.
The way leaves fall from ginkgo trees is a little different. The petioles of ginkgo leaves form the protective layer simultaneously and wait for a hard frost to trigger all leaves to drop at the same time, which results in a lovely shower of golden leaves.
So in fall of 2020, we had our hard frost really early when the leaves were still green and they dropped without turning gold, and so missed out on that annual treat, along with a few other weeks of October's usual delights.
Just one more way that this year has let us down.
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