Late (or Early?) Bloomers

Lately, I’ve been seeing strange things in the gardens I maintain.

It started in late October with a single white blossom on a weeping cherry that showed no signs of preparation for dormancy. I took notice but didn’t think much about it–after all, the tree had just been planted during the summer, and god knows what kind of bizarre conditions trees endure while they’re sitting in sweltering greenhouses, riding in pitch black box trucks, or baking at the nursery. I figured the poor plant just needed some time to readjust and overcome the biological jet-lag.

Rhododendron blooming

By late November, many of the large buds on the rhododendron above had broken, exposing white flowers that were probably meant for next spring.


But soon enough, I came across more plants that seemed wildly out of sync–and some of them seemed wholly confused, blossoming all over. Such an event, the development and expenditure of sex organs, represents a sizable investment of energy for the plant. But why would the rhodie above bloom in late fall, when we know that its primary pollinators have ended their working seasons, so to speak?


Sweet Bay Magnolia (Magnolia virginiana) Buds 2

Magnolias, like the one in the image above, are known for producing large and beautiful winter buds. Note the thick layer of fine hairs, protecting their delicate insides like some kind of tiny plant sweater.


Near the middle-to-end of the growing season, many plants form their flowers and leaves for next spring inside large, serious looking buds. These buds, which develop while the plant’s metabolism is still quite active, are often robust and well protected with scales. Winter buds are charged with protecting next years organs, and the fine hairs and waxy cuticle of their bud scales help prevent them from suffering freezing damage as temperatures plunge.


Late Blooming Rhododendron

I found the rhododendron above, of a different species, in full bloom around mid-November.


But back to our earlier question–why would a plant expend so much energy to such futile ends?

The answer is most likely in the weather. In New England, we’ve been graced with relatively mild temperatures throughout the fall, with few instances of frost. It is possible that these consistently mild temperatures have effected the signaling that determine the events in the life history of the plant. The study of the timing of these events is called phenology.

Another weather-related factor, a summer-long drought, may also have played a role in the late blooming of many species throughout the Northeast. During the dry growing season, as plants focused their energy on growing a root system deep enough to reach soil moisture, above-ground growth would likely be halted. Later, with the cooler and wetter fall weather, growth would resume in these upper parts of the plant. Flower buds may have received signals similar to ones sent in spring, encouraging bud swelling and breaking. In a sense, the hot, dry summer served as a kind of false dormancy period. You can read more about out-of-sync blooming in apple trees in Michigan here.


forsythia blooming late fall flower phenology

I was very surprised to see this forsythia, a species that typically blooms in very early spring, showing flowers during late November.


So why are these botanical anomalies important?

Consider the larger picture. The extreme weather, rising temperatures, and prolonged droughts that we’ve been experiencing on a global scale are likely a result of climate change. Such rapid and dramatic shifts in weather, which allow precious little time for evolutionary adaptation, are likely to throw plants and pollinators out of sync. In simple terms, this could mean lots of wasted energy on the part of both plants and pollinators, and a net negative effect on ecosystems and economies that rely on this important and delicate relationship.

On a more positive note, scientists can use these anomalies, and other phenological data, to study the direct impact of climate change on populations. The National Phenology Network maintains a database of phenological and climate-related data, and has developed a tool called Nature’s Notebook to allow scientists and civilians alike to collect and record data from the world around them.


Common Lilac (Syringa vulgaris) blooming

A common lilac (Syringa vulgaris) blooming in late November near my bus stop. The annual flowering of lilacs is a phenological even that is meticulously recorded by the NPN in order to understand more about the direct impact of climate change on this species.


These botanical mix-ups provide a valuable chance for us to witness the effects of a changing climate on the plants around us. By studying them, we can begin to predict what things may look like generations from now, and learn how we might mitigate or avoid the potentially catastrophic consequences of throwing the natural world out of sync.

And in the meantime, we can simply enjoy the flowers before they fade.

Thanks for reading,

Dan

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