I have some newly planted small shrubs and trees which are now in 3 inches of hard frozen snow. Everything was mulched well before it snowed. Yesterday I covered the plants with large inverted plastic pots, sheets, rice bags, and whatever I had at hand. The plants that are completely under pots will get no light. Can they stay in the dark through this entire cold snap (a week to ten days)? I’m not worried they will overheat under the pots,
with the sun so low in the sky, and the temperatures so cold, but should I be concerned with lack of light?
I have some personal experience with using just such pots to protect perennials, leaving the pots in place (and the plants in the dark) for a week or more. I would expect your plants to be fine. They will not overheat, though drainage holes help with air
circulation. Sheets and rice or burlap bags are fine as well, though the weight of
snow (in addition to the cold) can damage or break plants. You might want
to check the status of the covers if more snow falls. In addition, your mulching will help protect the roots. If the shrubs and trees are deciduous, they do not photosynthesize in the winter (low light and low moisture levels serve as the limiting factors, in general), so your plants will not suffer from the dark environment in
the short term. If the trees and shrubs are evergreen, they do photosynthesize in the winter, but the process is subject to the same limitations mentioned above. Again, no worries in the short term–frost can cause more damage to most plants than a few days in the dark.
Once temperatures are above freezing (32 degrees F or 0 degrees C)–and don’t forget to
consider nighttime temperatures–you can uncover the plants. Usually our
cold weather doesn’t last too long, so I think you can adopt the philosophy “better safe than sorry” and leave the pots in place until you are sure the cold weather has passed.
Below are some helpful links for additional information about predicting
frost and protecting your plants:
- If you are in the Seattle area, Gardening in Washington & Oregon (2005) lists first frosts as arriving “mid-November, earlier in the month to the north and the foothills.”Month-By-Month Gardening in Washington & Oregon
- Cold protection information from Oregon State University
- Frost guidelines from the Farmers’ Almanac