How Do Plants Survive In Winter?

You've probably noticed that some animals in our area, like hummingbirds, fly south for the winter. And many animals, like groundhogs hibernate, or sleep, during the winter months. Why? Their food source, green plants, aren't available any more. All plants depend on sunlight, water and carbon dioxide to grow. They create their own food (glucose) and release oxygen as a byproduct. The green pigment, chlorophyll, captures light energy and powers this process, called photosynthesis. But during the winter months, the shortened day provides less solar energy and freezing temperatures means water, essential for the process, is frozen and inaccessible. Plus freezing temperatures form ice crystals which rupture plant cells. So what's a plant to do?

First, as the days shorten and the cold sets in, many plants become “hardened”. Water is pumped out of plant cells into the roots and any remaining sap, moves outside of the cells, and becomes a concentrated sugary solution, acting like antifreeze. Broadleaf trees, like maples and oaks, shed their thin, flat leaves each fall to reduce water loss, sealing off the attachment point. Conifer trees and shrubs can retain their smaller, waxy needle-like or scaly leaves (pine, spruce, fir, cedars, junipers, etc) because they reduce water loss. Other evergreens, like holly and magnolia, grow tough, broad waxy leaves, which are more resistant to the cold and moisture loss. Plants also modify their life cycles, or rate of growth, to deal with the changing seasons and lack of moisture.

Some types of plants only survive for one growing season, dying back at the end of the summer or early fall. But their species survives because of all the seeds they created that will sprout the next year. These plants are called annuals. If you purchased pansies or marigolds for your garden last summer they are examples of annuals. The whole plant, roots, stems, and leaves die but the seeds endure. In order to germinate next spring, many seeds require a period of cold weather which our area certainly supplies.

Another strategy is to produce ground level leaves that are less susceptible to freezing temperatures, especially if they are under a "blanket of snow".  Many of these plants are biennials, growing for only two seasons. One local but non-native biennial, Burdock, grows in a circle, or rosette, of low lying leaves its first year. The next growing season the plant sends up long stalks with flowers that turn into the prickly burs (seeds). These burs, which stick to clothes or fur, are carried by unsuspecting wildlife, dogs and people to new places and begin their two-year cycle again the next year.

Conifers continue to photosynthesize during winter, albeit at a significantly reduced rate. But other plants enter a state of dormancy, or non-growth period, in the winter. Most broad-leafed tree and shrubs, along with herbaceous (soft-stemmed) plants, that live for two years (referred to as perennials) become dormant. They store their food, or sap, in their roots as mentioned above. Our native oak and hickory trees plus native wildflowers that appear each spring are perennials, surviving off the food stored in their roots during the winter so they can sprout again next spring. (Poison ivy is also a perennial, developing a woody stem that can be seen in winter, often climbing a tree as a vine or growing on the ground.

We have the change of the seasons, and this state of dormancy, to thank for a delicious and familiar tree product – maple syrup.  At the end of the winter and beginning of spring, sap starts rising up the tree's trunk to its branches. This sap, the tree's food, provides nourishment for the tree's new leaves, tucked inside a leaf bud, ready to unfurl. On warm sunny days the sap starts its upward journey. Cold, chilly nights slows or temporarily stops the progress of the sap's rise. When you drill a hole in any kind of tree this time of year the sap will drip out. But Sugar Maples have the highest sugar content (2%-3%) and their sap is used to make maple syrup, and sometimes taffy-like candy or granular sugar. Once the sap reaches the leaf buds the taste of the sap, and resulting syrup, changes and is not considered tasty anymore. The “window” for collecting maple sap is short and the process to create syrup is lengthy. Making syrup requires hours of boiling the sap to concentrate the sugar; forty gallons of sap makes only one gallon of syrup. This explains why the cost for 100% pure maple syrup is so high! Only a portion of the sap is collected each year so the trees remain healthy.

Just like animals, plants have developed ingenious ways to adapt to a variety of habitats - from the cold winters of the Midwest to the dry, hot deserts of the Southwest, even the arctic tundra of the north and rainforests of South America. It's essential for life on Earth. Why? Because all plants, from the tiny aquatic plants, called phytoplankton, to towering trees on land, are the basis of all food chains, including our own. Even the carnivore diet depends on plants to fuel the animal products!

To learn more about plant adaptations in winter visit here.