Plants, Fats & Cold Temperatures

For gardeners, knowing how to manage their plants during cold temperatures is important. Of course, as I write this at the end of December, the ground at my house is covered in four inches of snow. Perhaps then, an article about protecting your plants from the cold is too little too late. Instead, cozy up under a warm blanket and read about how plants deal with cold temperatures.

Plants have many mechanisms for dealing with cold temperatures. One not commonly discussed is the composition of fats in plant cell membranes as it relates to cold and heat tolerance. Look at it from the viewpoint of food: have you ever wondered why palm and coconut oil are solid at room temperature while most other cooking oils are liquids?

Tropical plant oils tend to be higher in saturated fats than temperate and subtropical plants species. Palm and coconut oils are solid at room temperature and are from tropical palm species. Other oils like canola, olive, peanut, and walnut to name a few, are liquid at room temperature and are from plant species that evolved in more temperate climates. The key is the relative melting temperature of the oils (fats) and how that relates to plant cell membranes.

Most gardeners are aware that plant cells are surrounded by a wall of cellulose which gives plants their strength and ability to grow upright. For non-gardeners, these cellulose cell walls are the fiber in your diet (eat your veggies!)  Fewer gardeners are aware that the lining inside the cell wall is a membrane that is essential to a plant’s well-being. Among the many things this membrane does is to behave like a “skin.” The membrane is responsible for keeping the contents of the cell (water, nutrients, proteins, sugars, etc.) inside.

The plant cell membrane is composed primarily of lipids–a form of fat. These kinds of fats depend on the plant species: plants native to the tropics have lipids with a higher concentration of saturated fats; temperate species have lower levels; and sub-tropical plants are somewhere in between.

Saturated fats have a higher melting point on average than unsaturated fats. That’s why palm and coconut oils, high in saturated fats, are solid at room temperature. Within a plant cell membrane, the average melting point of the component fats determine the membrane’s overall pliability. An adequately pliable membrane will be neither too brittle nor too soft for the climate in which the plant evolved.  A brittle membrane will crack and an overly soft membrane will rip open. Either case results in the cells “bleeding” their contents out. As you might imagine, this is very bad for the plant.

Back when I lived in a college dorm, I had a Dieffenbachia (a tropical species) as a houseplant in my room. Over winter break, I travelled home in temperatures well below freezing. Knowing the plant was very cold sensitive, I made sure my car was warmed up and tried to move it from the warm building to my warm car as fast as possible to minimize its cold exposure. Even though the plant was only out in the cold for 20 seconds at the most, the leaves of my Dieffenbachia turned water-soaked within minutes. They died even with the brief exposure to freezing temperatures.

The water-soaked appearance of the leaves was due to the plant cells leaking because the membranes had become brittle and cracked in the cold and the saturated fats couldn’t maintain adequate pliability. Incidentally, the stems survived and my plant leafed out again a month later.

Plants that survive winters in our region generally have plant cell membranes evolved to handle the wide temperature range we experience throughout the year. While proper plant selection is crucial for a cold-hardy garden, other factors affect winter survival. Now that you’re an expert on the effects of plant cell membrane lipid composition on cold hardiness, spend some time reading up on what a gardener can do to protect their plants from freezing temperatures.

— Content courtesy Moss Garden Specialist Darren Strenge