Winter Solstice in the garden | Garden Notes

The winter garden at Cornell Botanic Gardens features a central courtyard and concentric circles. Evergreens, holly, and other plants are woven into solstice traditions around the world.
The winter garden at Cornell Botanic Gardens features a central courtyard and concentric circles. Evergreens, holly, and other plants are woven into solstice traditions around the world.
Photo courtesy of Cornell Botanic Gardens
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As the winter solstice approaches, the sun travels its shortest path through our sky, marking the longest night of the year – and the return of longer days of sunlight. 

The solstice — Dec. 21 this year — is a turning point for plants, too. 

“We depend on plants for our food, shelter, and medicine, and plants depend on the sun. The return of the sun is the return of life and the promise that life will continue,” says Kevin Moss, student and public engagement coordinator at Cornell Botanic Gardens in Ithaca, New York. 

Kevin explains that many plants are woven into winter solstice and holiday traditions around the world. Across cultures, evergreens represent nature’s hardiness and cycle of rebirth. A Celtic tradition holds that bringing evergreens indoors gives woodland spirits and faeries a warm place to spend the winter, and in return, brings good fortune. 

In Norse mythology, mistletoe, an evergreen parasitic vine, signifies returning love and life to the world. Oaks, considered one of the most powerful trees, are the traditional choice for the Yule log burned on the night of the winter solstice. 

“It’s about bringing light into the darkness,”  Moss added.

Cornell’s winter garden is laid out with a central courtyard and concentric circles, ancient symbols for the sun and the circle of life. The garden features plants with persistent colorful fruit, exfoliating bark, and interesting growth forms like curly willow. Many are found in Pacific Northwest gardens, too: evergreens, dwarf conifers, winterberry, and deciduous trees like river birch, paper birch, paperbark maple, and hawthorne. Dogwoods can be coppiced every few years to produce bright, colorful twigs on full display in winter.

How are plants responding to the arrival of the solstice? Many have begun their winter survival strategies, surviving on the nutrients and energy stored in their roots. As the days shorten, their roots have released water, and the resulting concentration of sugars and starches acts as a kind of antifreeze.

Plants can track the length of daylight or darkness through special light-sensitive proteins, a phenomenon known as photoperiodism. According to Oregon State University research, the amount of uninterrupted darkness — not the length of daylight — plays the key role in determining flower formation for most plant types. 

Popular winter-blooming houseplants like poinsettia, Christmas or holiday cactus, and the tropical succulent Kalanchoe are known as “short-day” plants. Exposure to long nights of uninterrupted darkness triggers their growth response. Once the minimum threshold for darkness is met, the plant progresses from leaf formation to flower formation. 

Some summer-blooming plants and crops are “long-day” plants, requiring a short night to flower; examples include aster, coneflower, spinach, and potatoes. Others are “day-neutral,” and will form flowers regardless of day length; examples are begonia, geranium, tomatoes, and corn.

Indoor lighting can be used to manipulate light and darkness patterns and stimulate flowering. Adding light to a long-day plant to stimulate bud formation and early blooming is a common practice in the nursery and floral industries. Covering short-day plants at least
12 hours a day several weeks before their normal blooming period can stimulate early flowering. 

Outdoors, winter-flowering shrubs enter their blooming cycles as the days shorten and temperatures drop. Many are evergreen: heath and heather, hellebore, camellia, mahonia, daphne, and others. They can still be planted in early December if the ground is workable. 

Excessive artificial light at night can disrupt plant life cycles. It can also interfere with wildlife patterns such as migration, navigation, and reproduction. To help reduce these impacts, consider less disruptive outdoor lights with yellow, pink, orange, or red tints. White and blue lights can be shaded and facing down to reduce light pollution. The International Dark Sky Association (darksky.org) offers more information about outdoor lighting that can meet safety needs and improve efficiency while reducing unnecessary light. 

In winter, there is still plenty of microbial activity in the soil. Many microorganisms can withstand the winter cold. Their metabolic activity slows, but they continue to break down organic matter and release mineral nutrients to support plant growth in the spring.

Well-insulated soils — whether by snowfall or organic matter like compost, duff, mulch, or cover crop residues — are better able to absorb and store moisture. Layering organic matter in the winter garden has the added benefits of maintaining consistent soil temperature, helping deter weed germination, improving soil tilth, and preventing erosion.

Healthy soil also offers winter food and shelter for wildlife. Songbirds, toads, worms, spiders, and insects benefit from a rich layer of duff. To recreate what might be found in a healthy forest, use a combination of shredded leaves, twigs, moss and lichen fragments, conifer needles, and wood chips. Decomposers will break down the organic matter, releasing nutrients to support new spring growth. 

As we welcome the winter solstice, take a walk in a garden. If it’s a sunny day, observe your shadow, the longest of the year, at high noon. Celebrate the return of longer days of sunlight and new life in the garden. 

New! In 2023, Master Gardeners will partner with local libraries to offer in-person  “Ask a Master Gardener” plant clinics. The Port Townsend Library clinic will be from noon to 2 p.m. on the first Tuesday of each month beginning Jan. 3 in the Charles Pink House. 

The Jefferson County Library clinic will be from 1 to 3 p.m. on the second Saturday of each month beginning Feb. 11 in the Humphrey Room. 

(Barbara Faurot is a Jefferson County Master Gardener and Master Pruner, working with other volunteers who serve as community educators in gardening and environmental stewardship.)