Whether we realize it or not, most of us—at least here in the United States—have an impression of what it means when plants go dormant. The beautiful autumn leaves are part of the process of trees shutting down. And, the buds and glorious greens of spring are the end of the process, when plants are once again getting their juices flowing. The bare branches in between, during winter, illustrates dormancy.
Now, this then brings up the age-old question: Do the leaves change color if no one is there in the forest to see them? Obviously, this is a definite yes, and we don’t need philosophy to tell us that. The leaves change colors because sugars and chlorophyll are leaving them to conserve and store energy when it’s at a premium: winter. That stunning foliage happens whether we see it or not.
It would be very easy to let things rest there, but as curious purveyors of the garden, as powerful protectors of the planet, it is our duty and privilege to be more knowledgeable. So, let’s dig a little deeper.
What Is Dormancy?
Plants and trees go dormant in the winter. We easily recognize this. Leaves fall off of (deciduous) trees, and the landscape goes through an apparent change.
Just before this happens, people drive around and look at the autumn leaves, and by the same time next year, the whole cycle repeats. As mentioned before, this change in color is the result of sugar and chlorophyll leaving the leaves. The sugars, i.e. plant food, go down to the roots for safekeeping. Chlorophyll, what makes most leaves green, is integral to photosynthesis. Photosynthesis is how plants make sugars from the sunlight, but in the winter, this entire process is shutdown. Plants feed on the sugars stored in their roots, so the chlorophyll isn’t needed.
This is dormancy. It’s a state of metabolic inactivity for plants. That’s why we don’t say annual plants go dormant. They just die and grow back anew each year. However, perennial plants don’t actually die in this process. They more or less hibernate, living on the sugar reserves they compile during the rest of the year.
Why Plants Go Dormant
There is a good, logical reason for all of this happening. While most of us think of winter as being cold, there is another wintry characteristic that is very relevant to flora: The days are shorter. In fact, the further away from the equator we go, the shorter those days become. Shorter days mean less sunlight, less sunlight means less photosynthesis, and that means less plant food.
Even if trees were to stay active in the winter, the water moving through their leaves, branches, and trunks would freeze due to the severe temperatures, and the expansion of ice forming would do serious damage to the plant. In other words, though evergreens don’t lose their leaves (they have wax coating that helps to protect them), they go into a state of dormancy, too. It’s how trees survive winter.
Due to the lack of seasonal changes, winter dormancy—or autumn leaves—isn’t a thing in the tropics. Day lengths vary very little there, and temperatures don’t swing nearly as far. Though plants and trees in the tropics can go dormant due to other states of stress, such as dry season, they don’t put on the same sequenced color displays as seen in the temperate climates. It’s a reward for suffering the chilly winters!
Dormancy and Gardening
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For those who are getting into growing food at home, particularly perennial plants and food forests, plant dormancy is going to soon come to mean much more than bare trees in the winter. It’s a signal for when to do many different things in the garden. And, plants breaking dormancy too early can spell disaster for the coming year’s crop.
Typically, pruning fruit trees is best done when plants are resting (dormant). During this time, the insects and diseases that could challenge the plant are likely inactive as well. The plant also won’t have to use the reserved sugars to feed those branches that are clipped away. Plus, it’s easier to see the structure of the plant, as well as dead limbs, when it doesn’t have leaves. Dormancy is also the best time to plant or transplant trees.
The bad side of dormancy is when plants wake up a little too early. This typically happens when a warm spell comes on, tricks them into thinking its spring, and then a hard frost kills the new growth. Many temperate fruit and nut trees require a specific number of chill hours, above freezing but still below 45 degrees, before they break dormancy. Without these chill hours, they don’t produce well, which is why it’s very important to choose tree varieties suited to your particular climate.
Well, for sure, we have only scratched the surface of the science behind dormancy, but at this point, we could probably wow a few people with some facts and figures. And, hopefully, we can all walk away with a little more appreciation for what’s going on in the world around us.
Lead Image Source: Holly Vegter/Shutterstock