Can you believe that summer is halfway over?
As I woke up to a thick, gray marine layer over the skies of Hoquiam this morning, creating an autumn vibe already, I realized that I hadn’t seen much of the sun this summer. Quite often it would stay overcast all day with the sun only peeking out around 3 p.m., only to disappear again in two hours under another layer of clouds.
This got me thinking about the importance of the sun and fickleness of the weather on the life cycle of the plants in our garden ecosystems.
Before moving too much further, though, it’s important to recognize that the sun provides both heat and light; those are two different things. Heat at its simplest definition is a type of energy that freely moves from a hotter object to a cooler one. This can happen through radiation, convection and/or conduction. If you want to go down a lengthy internet wormhole, try searching “definition of heat” and you will get a crash course in physics.
While the sun provides much of the heat that gardeners depend on, there are other sources of heat for our gardens. These can be insulating materials (mulches, plastic sheeting, stone), structures (greenhouses), plant location (both geographically and in relation to other plants or structures in your garden), special weather events, changes in climate, and/or fire.
Why do plants need heat? Warmer temperatures are associated with an increase in the life processes (like photosynthesis and respiration). When it’s colder or when there’s extreme heat, these processes slow down. Additionally, seed germination and plant maturation can require certain temperatures and number of growing degree days to be able to complete their life processes.
Of course, there are many plants that are adapted to a variety of temperatures, such as spring bulbs that need a period of cold in order to bloom or the pine that needs fire in order to germinate its cones. It’s particularly important for us to monitor heat in the Pacific Northwest, because many of the vegetables that we find desirable need a little heat assist in order to cross the finish line. Also, some of our favored natives and colder weather-loving plants may need some protection from too much heat.
As I mentioned earlier, the sun provides both heat and light. Light is really the magic that plants have figured out how to master. Light is another type of energy, which is carried by particles called photons and moves in a wave. The colors we see with the human eye are different wavelengths and some are particularly important to plants. Again, be careful going down the internet wormhole searching for explanations of light!
Plants use blue-violet and orange-red rays for photosynthesis, the process in which they convert light energy into chemical energy. To me, this is one of the most amazing processes that has evolved on planet Earth. And it’s important to note that this is the cornerstone that all life on Earth depends upon.
Photosynthesis is by far the most well-known use of light by plants, but they have two more types of responses to light. Phototropism, a response to violet light, is responsible for the plant’s movement toward light sources. So, as you watch your garden grow, know that your plants are “seeing” the violet rays and trying to seek them out.
Finally, there is the response to day length, known as photoperiodism. This is a response to the amount of orange-red and far-red rays available during the day, and this can affect everything from seed germination and stem growth to dormancy and blooming. One of the best examples of this is the poinsettia, with its need for a lengthy dark period in order to bloom.
There are many things available to the average gardener to try to boost the amount of heat for your plants. But if you don’t pick the right plant for the right place, or if the weather or climate conspires against you, you may be out of luck on getting enough light.
I hope this gives you some food for thought on the influence of the sun’s heat and light on our garden, and what we can do about it!
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Interested in the WSU Master Gardener program? Check out PNWMG.org for information and applications. Training starts in February.
Katie Lutz, from Hoquiam, joined the WSU Master Gardener program in 2016.