Plants know when spring is around the corner. But how?

Maybe I have a faulty memory, but I really can’t remember a worse winter: Snow, ice, rain, melt, freeze, thaw again. Oh and the wind and utter lack of sun for days on end. Of course, you don’t need me to tell you this.

Yet this week, while literally sliding my way down our steep driveway to get the mail, I happened to spy some already green and downright fat buds on sumacs. What an amazing thing to see, considering the awful weather.

It is time for some admiration for our plants and how they operate. Specifically, what is it that triggers our plants to start growing again after the long winter? If I have it right, it is light receptors in our plants that keep track of the number of night hours. These receptors are called phytochromes. It turns out fungi and bacteria have them as well.

Most humans tend to dis plants because they can’t walk and don’t have any apparent brains. Gardeners shouldn’t. Think about it. All of our plants, save the evergreens, drop their leaves in the fall. Still, those phytochromes keep track, and when nights lengthen enough, they stop the plant from conducting photosynthesis. Sugars in the above-ground parts of the plant are transported to storage in the root system, where they are converted to starch, a much more viable storage molecule.

It is pretty complicated, but amazing stuff. All through the winter, plants keep track of night hours. Remember, most don’t have any above ground, or at least above snow, presence. When there has been enough darkness, phytochrome signals are sent out, the stored starches are converted back to sugars, transported to meristem tissue — think stem cells as well as birch and maple syrups — and provide the energy used by the plant to produce what is needed for growth and renewed photosynthesis.

However, we have all seen “early” springs. Why does growth start earlier when we have warmer weather? How can that be, if it is the darkness that triggers them? The answer came only about five years ago, when scientists discovered some phytochromes switch roles at night and act as temperature monitors. When it gets warm enough at night for growth to start, the signal goes out regardless of night hours.

When it gets warmer earlier — think global warming — those nighttime phytochromes start the plant growing. Ah, then there are freeze and thaws and the plant can’t hold on. It dies or weakens, making it susceptible to pathogens and insects — think bark beetles.


These phytochromes are the reason we like native plants. They “get it” and know when to start growing. The problems usually occur with non-native perennials that have not adapted to our long winters and the rapid changes in hours of daylight and swings in temperatures. However, even our native plants are susceptible to global warming — again, think spruce bark beetles.

No big advice this week, save that it is time to look around and notice the changes in our plants. The subtle red and green hues of spring buds are starting to appear, and gardeners should stop and marvel a bit at our plants’ capabilities. Consider that everything, from bud to leaves to flower and fruits, are all produced by the plant through biosynthesis. It all starts with a few signals sent about this time of year, snow or no, by some phytochromes.

Jeff’s Alaska garden calendar

Alaska Botanical Garden: Kick off the gardening season with a virtual spring garden conference, 2-8 p.m. Friday and Saturday, March 11-12. Register at

Vegetable seeds to start: Celery. Tomatoes if you have a greenhouse or room.

Flowers to start: Sweet peas. Pinch them back to “bush” them up.

Seed racks and garden plans: Careful. Still, you need to buy seeds. Just make a plan before you buy.

Jeff Lowenfels

Jeff Lowenfels has written a weekly gardening column for the ADN for more than 45 years. His columns won the 2022 gold medal at the Garden Communicators International conference. He is the author of a series of books on organic gardening available at Amazon and elsewhere. He co-hosts the "Teaming With Microbes" podcast.