A viburnum, normally a spring bloomer, set blossoms in the fall in this Portland garden, pictured in October. Photo by Peggy Grodinsky
Shrubs and trees that normally bloom in the spring seem confused this year. They bloomed as usual in the spring, but some have been putting out new blossoms in September and October.
I have had readers email me photographs, or I’ve seen myself, blossoms on viburnums, forsythia, honeysuckle vine, beauty bush, rhododendron and magnolias. Other years I’ve heard of the same phenomenon happening on fruit trees.
My initial reaction? Relax and enjoy it. It may be the world getting weird, but many of us grow these plants to enjoy the blossoms. If we get a few unscheduled fall bonuses, it’s just a bit more pleasure as the garden season draws to a close.
Worriers, however, note that while the blossoms are nice, climate change is also producing rising temperatures and drought, which lead to more wildfires, as well as unusually heavy rains, which lead to floods such as those that occurred in parts of Maine and the rest of New England this summer.
Bryan Peterson, an assistant professor of horticulture at the University of Maine, said he sees some amount of fall blooming most years, but it does seem to be happening more in 2023.
“I tend to view this precocious flowering as a phenomenon that follows periods of drought stress, so I’m not entirely clear about what is causing it this year,” he said.
Pamela Hargest, a UMaine Cooperative Extension educator based in Falmouth, said any kind of stress can trigger reblooming, including too little or too much water.
A rhododendron, which normally blossoms here in May and June, rebloomed this fall. Photo by Tom Atwell
Beyond climate change, fall blossoms come with a price: fewer blossoms next spring.
“Spring flowering trees and shrubs bloom on old wood, from buds that are set during the previous year,” Peterson explained. “When this precocious blooming occurs, the number of buds remaining to open in the spring decreases.”
The good news: Energy the plant spends on the fall blossoms will not affect its overall health.
Fall blooming occurs frequently on apple trees, Peterson mentioned, but the out-of-season blooms do not reduce the apple crop because farmers trim the trees each year as a way to produce fewer but larger fruits.
The science of reblooming is related to how certain plants – Peterson mentioned quince and cherries in addition to apples – have less control of when their buds break out of dormancy. Plant breeders in the horticulture industry have taken advantage of this characteristic, he said, by conducting controlled cross-breeding to create cultivars designed to bloom in spring and fall. Examples of such plants include “Bloomerang” lilacs, “Summer Snowflake” doublefile viburnum, and the “Sonic Boom” series of weigela.
Peterson noted that the trade-off with cultivars that bloom twice is that the spring blossom is less intense. Many gardeners are willing to accept that to get the longer bloom time. I, however, am a traditionalist, and my wife and fellow gardener Nancy and I have yet to plant any of these extended-bloom cultivars. We’re settling for — and enjoying — the occasional surprise magnolia bloom in September.
Tom Atwell is a freelance writer gardening in Cape Elizabeth. He can be contacted at: tomatwell@me.com.
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