'Twas the week before Christmas and all through the yard,
Not a plant is stirring, the soil nearly frozen hard.
Tired gardeners are nestled, all snug in their beds,
While visions of dormancy danced in their heads.
Just imagine what it would be like...
Snuggled up warm and cozy while the world outside is cold and dark, you enter a deep and peaceful rest. Your cells are protected from freezing. Active growth is paused. This slumber is essential for your long-term health and prepares you for a burst of life and new growth when spring returns.
Snap out of it!
As much as we may want to get on that train, winter dormancy is for plants and bears, and they're keeping this trick all to themselves.
The reduced amount of sunlight and warmth a plant receives in the fall tells the plant that it's time to go dormant. As daylight declines, plant roots produce abscisic acid. This hormone tells the plant to reabsorb all the nutrients it puts into its leaves for photosynthesis. As these nutrients are reabsorbed, leaves can turn yellow and red.
When temperatures drop, sugars, salts and other nutrients are stored within a plant's cells to protect them from freezing. Roots stay protected by soil, mulch and snow. Water and other nutrients are held in the roots until the days become longer and growth resumes.
There are two types of winter dormancy. In endo-dormancy, the plant won't grow even if conditions are warm and favorable. Factors inside the plant are inhibiting growth. Eco-dormancy occurs when the plant is ready to grow, but environmental conditions are unfavorable. Usually, it's too cold. Endo-dormancy occurs first, induced by autumn's short days and freezing temperatures.
As the plant enters endo-dormancy, it tracks chilling units to mark the passage of the winter. Chilling units are hours of time spent above freezing. The number of hours required for chilling varies for different plants from less than 500 to 1,500 hours or more.
Most people assume the plant is tracking hours below freezing, but that's not the case. Hours below freezing have no effect on chilling, but they will make the plant hardier. If warm weather occurs before the plant completes its chilling requirement, no growth occurs.
Chilling and endo-dormancy normally prevent plants from beginning growth during the brief warm spells that surprise us in the middle of some winters. Not all hours above freezing are equal. Temperatures between 40- and 50-degrees Fahrenheit are most effective. Temperatures just above freezing and above 50 degrees are less effective, and temperatures above 60 degrees often have a negative effect on chilling.
In endo-dormancy, plants have the ability to survive in very cold weather. This is referred to as the plant's cold hardiness. Maximum cold hardiness is reached when plants have been exposed to cold, subfreezing temperatures for several days or more.
After chilling is completed, the period of endo-dormancy is over, and plants enter eco-dormancy. Now, the plants are dormant only because of cold temperatures.
Warmer temperatures into the mid-40s will cause them to break dormancy and begin growing. Once the plants start to grow, they lose the ability to readjust to colder temperatures, and damage can occur.
Ideally, there is a gradual progression of development and the plant begins growing in response to slowly rising temperatures. We notice buds swelling and green tissue emerging, but actually, the plants broke dormancy before we notice the visible changes.
Environmental cues are not the only factors that regulate a plant's acclimating to cold weather. Cultural conditions, such as long, warm autumns that promote late season growth, can delay dormancy and the acclimation process.
Pruning and fertilizing in late summer or fall stimulate new growth and delay dormancy.
In arid climates such as ours, going into winter with high soil moisture offers protection for the roots of woody plants. Soil temperatures drop more slowly in moist soil due to the heat of fusion generated by the freezing of soil water, keeping the roots warmer than air temperature during cold spells.
Besides tired gardeners, not all plants go through dormancy. Annual plants live out their entire life cycle in one season, and evergreens stay active all year long.
With all the hustle of this holiday season, it's a blessing that our gardens need little attention during December. Take a walk through your garden and marvel at nature's quiet resilience. Make time for a short winter's nap this week to refresh and recharge. Before we know it, it'll be time to curl up with seed catalogs and dream of next year.
Right now, my garden sleeps in heavenly peace.
My wish for you is the same this Christmas season.