Only a few degrees make a difference. In December, a sunny day approaching the high 50s brings smiles right after days of cold or stormy weather.
Up the notch just a bit, and we slow our activity to soak up the rays, commenting to each other about what a beautiful day it is.
And so it is for many plants. Warmth may bring germination of seed in soil moistened by steady rains. Bulbs push young green leaves through the mulch of fall leaves. Winter vegetables growing, perhaps with some protection, respond.
Violets are the first perennial to open in the warmest spot at the base of a bench I have against a south-facing wall. Even flowers expected to bloom in late winter and early spring seem to be budding with heightened expectation.
Ornamental grasses, at their peak in the fall months, may still have beautiful color or form in a protected December microclimate. Cutting them back may be delayed until January or even February.
As I watch the rose hips along the Colfax highway color in December, I am struck by the differences between the warmer north side of the highway and the south side, which is cooler.
The California native rose seems to thrive in the warmer microclimate, setting more fruit, and the rose hips are a deeper color. The winter sun, low in the sky, lights these wild plants. The fruit seems to glow.
Approaching the winter solstice, even gardens in full sun are cold and have less light. Microclimates, created or natural, influence plant performance during this seasonal shift. The smaller climate zones within a larger climate are found throughout the foothills. Hills, valleys, bodies of water, canyon slopes, exposure (east, west, north, south) all influence plant growth. Within these microclimates are even smaller microclimates.
My own landscape has warmer winter microclimates, such as the slope to the east, and colder zones where the cold winter air slides down the east side of Sonntag Hill and covers like a blanket the small apple orchard and my nearby vegetable garden situated on a knoll at the base of this slope.
I have written before about my latest spring frost June 13 one year.
Walls facing south may protect a garden bed enough to grow plants that are marginal in winter hardiness or slow to grow in a more exposed microclimate.
While my eastern slope seems to be the better microclimate for growing winter vegetables, I can coax still more warmth from the December sun by creating a wall with straw bales and planting in compost at its base.
In Scotland, I found that ancient walls protect many older gardens. At Cally Gardens, near Gatehouse-of-Fleet, the walls are 14 feet tall.
The walled garden is three acres, originally an edible garden that once fed inhabitants of the surrounding southwest Scotland countryside. With that large an area, protection from prevailing winds would be optimized close to the wall blocking the wind.
Individual glass cloches once protected edible plants in Europe. Similarly, small portable cold frames allow light and provide warmth. The side panels and cover of the Juwel cold frame are easily set up and dismantled for storage.
Hoop houses and greenhouses provide larger microclimates for growing but are quick to overheat on a sunny winter day.
For years, I have used a product called Tufbell, a row cover that protects the winter vegetables, including cover crops. The cover allows good light transmission and does not overheat the protected crop. Rain penetrates easily. The cover also protects plants from hail damage.
Agribon offers several grades of row covers for seasonal protection. AG-50 provides the greatest frost protection but also allows the least amount of light. AG-30 may be a better choice if you want to leave the cover over the plant or crops until spring.
There are even lighter grades that may be used for insect (and bird) control and light frost protection.
While you are thinking warmth for your plants as we approach and pass the winter solstice, also plan a sitting area for you, where you can linger midday when the sun is out.
Carolyn Singer has gardened organically in Nevada County since 1977. She is the author of “The Seasoned Gardener, 5 decades of sustainable and practical garden wisdom”, now available locally. For more information about foothill gardening, or to contact Carolyn with gardening questions, visit www.carolynsingergardens.com.