In parts of the country that do not experience our kind of cold weather, plants do not have to go dormant. Many houseplants typically live outdoors year round in other parts of the United States or the tropics.
Deciduous plants in our region evolved ways to remain alive during the winter months and wait for better weather to return. In the spring, they break their winter dormancy and begin to grow and flower for the coming year. This dormancy mechanism includes allowing the leaves to move any nutrients out of the leaf and into stems, buds, trunk and roots to be stored for next year. The leaves are lost to cold weather, yet still benefit the plant by being recycled as they break down and add organic matter to the soil. The trunk, branches and buds have developed what we know as bark and bud scales to insulate the vascular tissue and bud initials respectively. Take a look at your houseplants again. Many of them just have a green stem that would easily be frozen if left outdoors. If you have a good green thumb and can keep the same houseplants for years, some will develop woody stems since they may be large growing shrubs or trees in their native locations. A couple of examples would be the Weeping Benjamin Fig and the Rubber Tree. The Poinsettia plant given during the holidays can become woody and is several feet tall and wide where it grows natively.
While most of our perennials can survive without any snow cover, they will do better if protected, especially those that have shallow roots and crowns. The freezing and thawing cycle in the soil can push them right up to the surface. Roots are easily damaged and killed in this environment. This is why the snow is so helpful. Snow moderates the soil temperatures, minimizing the freeze-thaw cycle. The snow also protects the crown of the plant, as this is where all of next year's growth will come from.
Since our deciduous plants have evolved to survive our winter weather, they also need that signal to return to growing from being dormant. Our spring thaws and rains begin to trigger that along with warmer days and warming soils. So look outside, enjoy the white snow cover in your yard, and keep your thoughts on the coming spring!