Winter Solstice

At exactly 8:28 AM, on December 21, 2017, the northern hemisphere of planet Earth was tilted as far away from our sun as it gets. [The Earth is actually as close to the sun as it gets between the 3rd and 5th of January, but we are tipped away, so we don’t notice.] So, how is your garden affected by winter solstice?

What is winter solstice?

Before we learn how shortening and lengthening days affect your garden and landscape plants, let’s take a moment to discuss what, exactly, is meant by winter solstice. The word solstice comes to us from the Latin words for sun (sol) and “to stand still” (sistere). Obviously, the sun and earth never really stop moving. It’s an illusion that refers to the two extremes of the Earth’s travels around the sun.

​We all know that the Earth has an equator around the middle and poles at either end, except those ends are not exactly up and down. The Earth is tilted 23.5° (23.44°, if you want to be really accurate). This means, for half of each trip around the sun, the northern hemisphere is closer to the sun, while the southern hemisphere is closer the other half of the year. You can see it easily if you hold one hand up at an angle and the other up as a fist. Your fist is the sun. Move the slanted, open hand around your fist, keeping the angle pointing in the same direction the whole time. Moving from one side to the other, you will see that different parts of your open hand are closer to your fist. When either hemisphere is at the farthest point from the sun, we call it the winter solstice. Six months later, when we are as close as we will get, we call it summer solstice. So what does this have to do with gardening?

Earth’s rotation (NWS) Public Domain

Why does it keep getting colder after the days start getting longer?

Simple logic tells us that longer days should mean warmer temperatures. Experience has taught us otherwise. But, why? Even though the days are getting longer, we will not see our coldest temperatures until January and February. It ends up that our planet’s temperatures are largely controlled by its oceans. It takes a lot of time and sunlight to heat up an ocean. 

Dormancy and frost damage

Most perennial plants go into some sort of dormancy as the number of daylight hours shorten and temperatures drop. Life process are slowed, new leaves and buds stay protected within buds, and many chemical changes occur that protect the plant from winter’s cold. You can protect your garden plants from frost damage during dormancy by adding a protective layer of aged compost, mulch, straw, or even a fabric covering around and over (but not touching) your plants. Keeping plants well irrigated, but not soggy will also protect against frost damage. Maintaining a more constant temperature can help your plants avoid falling prey to one warm day that might trigger budbreak, when the following days of cold and frost would simply kill those tender new buds and shoots.

Stonehenge (Andrew Dunn) CC BY-SA 2.0

Winter solstice in history

Rather than risking stress to your plants by working in and around them in the cold, use this day, as people have throughout history, as a truer new year, to look back on lessons learned and accomplishments reached, and then forward, to new and existing goals, both in the garden and in life.

Did you know that Stonehenge was built to line up with sunset on winter solstice?