I have to face it. I am a nerd. More specifically, a science nerd. This has become abundantly clear after writing four books — great holiday gifts, by the way! — that try to decipher complicated plant science. I try not to let it show out too much in these columns.
Knowing this, it should come as no surprise that I cannot stop thinking about how our trees and shrubs survive below-freezing temperatures. We have had our share of late.
I know most think of plants as nonsentient organisms, but they are obviously very good at surviving all manner of conditions, so something must be going on. They adapt extremely well despite their lack of brains or an ability to simply move to better conditions.
From a plant’s perspective, the problem is that water expands as it freezes. And when water inside a cell expands, the cell bursts and dies. Plants prevent this first by increasing the flexibility of their cells’ walls so they can expand somewhat. If this isn’t going to work, they move water out into intercellular spaces where it is OK to freeze because there are no membranes to constrain it.
Finally, it shouldn’t surprise anyone that plants also produce special proteins that serve as antifreeze. Roots handle frozen conditions by using sugars and producing proteins that lower the freezing point of water so ice doesn’t form inside the roots. These are called cryoprotectants, and they prevent frost from destroying root cells.
We all know our trees shut down when it gets cold. Without leaves, there is very minimal metabolic activity and most of what there is happens to be protective in nature. As for evergreens, their needles are designed to conserve moisture in winter.
The water pipes inside our plants are composed of xylem cells that are susceptible to freezing damage. As cold weather approaches, they slow and then stop water transport. As they enter this dormant state, they develop thicker walls. Some even produce cells that seal off areas susceptible to frost damage. Others produce air bubbles to prevent damage when it is below freezing.
The food transport cells are the phloem cells. They concentrate sugars when it gets cold and that greatly lowers their freezing point. As with the rest of the plant, phloem cell membranes change so they will be more flexible, which helps them handle expanding water.
Of course, there is a lot of specialized genetics involved. This is why you cannot just take a maple tree from Minnesota, where it is colder than here, and get it to survive. One important factor here is how quickly a plant can readjust to the onslaught of spring light or learn and adjust when winter is approaching.
Obviously, plants are far from inanimate and obviously I am a nerd for thinking about our freezing plants. Be warned: I will be just as nerdy when it warms up and all manner of exciting things start happening inside plants as they reactivate.
Jeff’s Alaska Garden Calendar:
Alaska Botanical Garden: All I want for Christmas is for all of you renew your membership or get one and support The Garden. There is no better present to me or to any gardener than a membership in The Alaska Botanical Garden. It is inexpensive but supports so many worthy people and events, not to mention plants. Do it now.
Pelargoniums: Pot yours up or put potted up plants under lights and have flowers in a month.
Trees: Having a tree inside a house requires constant vigilance if you have lights on it. Check that it has water every day.