I think back to when I started writing these columns. They served a dual purpose: providing readers with a notion of what to do in the yard and when to do it as well as serving as letters to my father back in New York telling him what I was doing in the yard each week.
Flash forward almost 50 years and I am still dwelling on what to do and when to do it. However, over these years of trying to answer others’ questions about plants, I couldn’t help but develop a deep curiosity about what is happening inside plants and how they operate. This streak of curiosity is codified in four — best-selling! — books known as the Teaming Series. One of these books delves into how plants actually take in nutrients and what happens to them inside the plant.
Looking back, however, I see I have never properly addressed what several readers wanted to know last week: How does a plant survive a temperature of 24 degrees below zero?
My past answers point out that plants create antifreeze that lowers the freezing point of the water. I think I can do better, just in case you too want to know.
First of all, let’s address ice. The problem with it is the crystals it forms. Their formation causes water to expand, which alone can cause damage inside a plant cell. In addition, ice crystals are sharp so they pierce and kill cell organs and organelles and even cell walls, causing the remaining liquid inside the cell to leak.
Next, the plant cell. Each has a wall inside of it, a membrane that controls what moves in and out of the cell. What is astonishing is that the cell walls can hold water and all are connected to the surrounding walls. By way of illustration, if you have a tiny kayak, you could move throughout the network of plant walls, from stem to leaf cells, around the stomata, out a stem and into another leaf, all without moving into a single plant cell. This canal system is known as the apoplastic pathway.
Sorry, I am getting into the weeds — wrong term. Suffice to say protection from freezing is different than protection from chilling, which uses sugars to lower the freezing point of water.
When winter hits, cells in those plants that survive our winters take in nutrients and make what they need for protection. First, they add fatty acids to those membranes. This keeps them flexible when it starts to go below freezing so water, sugars and other molecules can move in and out.
These same cells also make special amino acids that are then assembled into specific proteins which prevent and stop ice formation. These are moved out through the membrane into that apoplastic pathway. So is much of the cell’s water. The proteins then stick to forming ice crystals preventing them from growing and damaging the plant.
This all makes sense. Sure there is some antifreeze made and impurities needed for ice nucleation are too. But, it would take one heck of a lot of antifreeze to supercool a plant for nine months. Preventing the damaging crystals from growing in the first place is a better way to go.
All of this leads me to the point of amazement. Fifty years ago I viewed plants as non-intelligent and doled out advice as if we gardeners were necessary for their growth. Now I appreciate that plants are really so much more and so amazing. Every day I appreciate them more.
Jeff’s Garden Calendar:
Alaska Botanical Garden: Spring conference is March 23-24. Also The Garden is hiring. Join!
Seed racks: They are coming. Don’t be overly tempted.