My friend Jane Antley lives in the borough of West Chester. She emailed me last month with a question about leaf drop. “I’ve been meaning to write to you for several weeks about something that has me perplexed this year: the Japanese red maples. Sure, we’re all aware that they didn’t turn their glorious red this fall, as so many other trees, too, had disappointing fall color. But what’s got me really curious is how they have held on to their leaves this winter. They seem to be steadfastly holding on to their ghostly looking leaves. I am surrounded by these trees in my area, so I notice it every single day. What do you think?”
The first, most intriguing thing to me about Jane’s question was that I hadn’t noticed anything unusual in my neighborhood. As she mentioned, she is surrounded by them. Maybe there just weren’t many in my immediate area. The second most interesting thing is that ever since I received Jane’s email, once I get out of my own little neighborhood I’ve been seeing Japanese red maple trees everywhere. And, just as Jane had noticed, their branches are still covered in dead leaves.
Fortunately, the internet makes it easy to search for information on unusual topics and I hit “pay dirt” within about five minutes. George Weigel is a Pennsylvania horticulturalist and garden writer who writes for Penn Live, the online arm of the Patriot-News in Harrisburg. Back in December 2015, he fielded the same question from a reader who wrote about a single Japanese red maple tree in his yard. Weigel’s best guess at the cause for the phenomenon was a cold snap in early November that year.
He wrote: “What I suspect happened is that the cold spell we had in early November froze maple-leaf and maple-twig cells before they had a chance to complete their normal winter-prepping process.” (http://blog.pennlive.com/gardening/2014/12/why_arent_the_leaves_falling_o.html)
There are two basic processes that deciduous trees go through every fall. Both are impossible to miss. One, with waning daylight hours and decreasing air temperature, trees are prompted to stop producing chlorophyll, the pigment that gives leaves their green color. The brightly-colored yellow, red, and orange pigments are always present in trees leaves. They’re just not visible until the chlorophyll backs off.
Two, the trees start producing an abcission layer at the end of the leaf stems. This cuts off the leaves from their food supply and separates the now-dying leaves from the tree. A little encouragement from the wind and down they’ll come. However, as Weigel explained, unusually cold temperatures too early can thwart the process. “Not only does the leaf color go directly from green to brown, the leaves stay attached because abscission tissue hadn’t sufficiently developed.”
For the Japanese red maples, reports Weigel, something else may also affect the process. It’s possible that because they are understory trees, often protected somewhat by taller trees, the Japanese red maples tend to take longer to go through the abcission process. Sounds plausible.
There was just one more question to answer: did we have a cold snap last fall? I went back online and found a site containing historic weather data. I was reminded that after a summer-like October — with daytime temperatures in the 70s and 80 — on November 10th, 11th, and 12th we had a cold snap, with the nighttime temperatures in Philadelphia dropping to 25, 23, and 30 degrees respectively. (https://www.timeanddate.com/weather/usa/philadelphia/historic?month=11&year=2017)
According to Weigel, as spring weather returns we can expect to see the brown leaves drop off — just as oak or beech leaves do — and a new season of green leaves emerge. Something to look forward to!
Pam Baxter is an avid organic vegetable gardener who lives in Kimberton. Direct e-mail to firstname.lastname@example.org, or send mail to P.O. Box 80, Kimberton, PA 19442. Share your gardening stories on Facebook at “Chester County Roots.” And check out Pam’s new book for children and families: Big Life Lessons from Nature’s Little Secrets. Available at amazon.com.