Before diving into this week’s topic of how plants survive the cold, I’d like to give you an update on my hydroponic experiments.
After a month, all but one pod has sprouted. This is good by my standards. Seeds do not always germinate. Dill came first, followed by some basil plants, then parsley, chives and mint. The water tank he only had to refill once early last week and is adding more nutrient solution every two weeks. The dill is big enough to harvest, and the parsley is just around the corner.
Now let’s talk about how plants survive the cold. Winter is in whiplash mode so far. Last week it was -9 degrees in my yard, this week it’s below freezing. Last week was the coldest weather since 2010. This is within the USDA Zone 6 tolerance, which states that plants rated in this zone can survive at least 10 degrees below freezing. The tricky part is when the wind chill factor comes into play. It can damage or kill otherwise hardy plants.
The first thing our plants are currently doing to their advantage is snow cover. I have more than a foot of snow in my yard, which keeps the roots and lower stems from the cold. strengthen the
To further protect themselves, plants go through a dormancy process that prepares them for the cold. After the equinox, when light and temperature levels drop, trees begin to transfer water and nutrients from their leaves and stems to their roots. However, this year, the leaves withered due to the coldness of early winter, and that also had an effect. When excess water is removed from the stem, the plant cells are less likely to freeze and burst. When water freezes, it expands and breaks down the cell walls, causing the plant to die. Water and nutrients are drawn into the plant’s deep roots, where the ground is warmer and adds protection.
But what about evergreen shrubs and conifers? Most evergreens go through the same dormancy process but keep needles. Local exceptions are the needle-dropping tamarack and dawn redwood trees. Otherwise, coniferous needles have a thick cuticle coating that protects them from the elements, especially wind.
Evergreen shrubs such as rhododendron, Oregon grape, holly, and cinnamon also undergo a dormancy process, but the leaves remain alive. They are more susceptible to deep cold combined with wind that can dry out and kill the leaves. Fortunately, the leaves regrow quickly in the spring. Uniquely, rhododendrons roll their leaves inward when temperatures drop below freezing. The colder it is, the tighter it rolls. This prevents exposure to winds that dry out the leaves.
Correspondent Pat Munts can be reached at email@example.com.