Dormant plants wait out the cold, dark winter — so can we
Perhaps this year more than most, winter is going to be a cold, dark time. We’ve retreated to shelter, waiting for a dangerous season to pass. If we were plants, we’d be dormant.
People are accustomed to gathering in the darkest times of the year, celebrating our connections and making our own light. Plants have a different strategy.
“The plants in our yards are dormant every winter,” said Julie Janoski, Plant Clinic manager at The Morton Arboretum in Lisle. “Their regular routine is to sleep through the worst times and wake up again when things get better.”
Dormancy is a strategy that plants all over the world have evolved to survive periods when resources, especially water, are scarce. They stop their growth, let go of anything that is not essential, store nutrients in their roots for safekeeping, and keep their vital processes at a minimum until more resources become available.
In tropical rain forests, plants often go dormant during the dry season. In deserts, many plants are dormant almost all the time, barely growing, hoarding moisture. A rare rainfall can make the desert bloom as plants seize the chance to flower, trade pollen to fertilize each other’s blooms, and make seeds. As the land dries up, they subside again into dormancy.
Winter is the tough time in the Midwest. The air is dry and cold winds are cutting. Water is essential to all the living processes of a plant, but not if it’s frozen — ice crystals are shards that tear cell walls. Roots can’t soak up ice, so even if there’s frozen water in the soil, plants can’t use it. They cope by going dormant. In most trees and shrubs, the coming of dormancy is easy to see in autumn, when they let their leaves dry out and fall from the branches. To store nutrients and water safely in the insulating soil, trees spend the fall expanding their underground root systems. Water drains down from twigs and branches into the roots, along with sugars and starches that will be stored to fuel spring growth. Leaf and flower buds that have already been formed for next year are armored inside tough bud scales against the cold and wind. Wrapped in protective bark, a tree can sleep and wait.
Down along the ground, most perennial plants let their green growth die altogether. Only the roots and bulbs survive, dormant, until spring. “They are safe in the soil, especially if there’s a layer of mulch for insulation to keep the temperature steady,” Janoski said.
Seeds, too, lie dormant, each containing a tiny plant embryo protected by a sturdy seed coat.
Evergreen trees and shrubs that keep their green leaves all year are never completely dormant. “They slow down, but they continue to function at a lower level during the winter,” she said. “They still have moisture in their leaves, which makes them more exposed and vulnerable to winter damage than plants that go dormant.”
Dormancy is built into the life cycle of most trees, shrubs and other plants in the Midwestern climate, but it also can be a response to stress and catastrophe. A tree that is threatened by drought may go dormant early to conserve resources and survive.
There is a price for this. Leaves, stems and flowers are costly to make, in energy and nutrients. When a plant discards them to enter dormancy, it gives up those investments in exchange for protection against hard times.
Yet dormant plants haven’t lost everything. They keep their roots.
They keep their connections with the soil and the fungi and other life forms that live in it. They keep their genetic memory of how to grow, bloom and thrive. When the soil warms, when the days grow longer, when the rain comes, they will be ready to wake up, emerge and rebuild.