Every year late in the fall we field questions about potted evergreens for use as Christmas décor. On the surface, it’s a slam dunk! You’re not needlessly killing an evergreen to decorate, and you’re saving money. Some people intend to plant the evergreen the following spring, while others plan on keeping the evergreen potted indefinitely, hoping to use it again each winter.
However, as we’re all acutely aware, Canadian winters can be cruelly cold. A hard winter can quickly spell doom for potted evergreens even though we have the best of intentions.
Take heart! We aren’t in the business of crushing inspiration, and we certainly aren’t suggesting that the idea of potted evergreens be thrown out of the metaphorical window! However, the difficulty of successfully wintering over an evergreen in a pot in Canada is, in a word, substantial.
In today’s post we’re going to walk through some of the challenges of overwintering a potted evergreen, and some steps you can take to improve your chances.
The Challenge
The roots of our plants are more susceptible to cold damage than any other part of the plant. Generally, temperatures of -10⁰C or lower will freeze and kill the roots of all but the toughest plants. That’s not even that cold: the average low in London in January is -9⁰C. How do our plants survive?
Interestingly enough, many of the elements of gardening most critical to our plant’s survival during the growing season – that is, soil and water – play just as pivotal a role for our plants in the winter.
Long story short, soil has a substantial insulating effect on roots, and sufficient moisture makes it harder for the soil to completely freeze. While the air temperature might be a frigid -20⁰C, averagely moist soil could be anywhere from 10 to 12 degrees warmer at a depth of 2 feet. Mulch and snow have an added insulating effect (which is why we encourage our customers to mulch their plants!).
As you might suspect, keeping evergreens in a pot above ground removes many of these safeguards. There’s also a distinct possibility that even if your evergreens do not die, they will suffer damage or dieback and will look unsightly the following season. This is an incredibly difficult problem to remedy, but there are some precautions you can take.
Protective Measures
- Consider picking tough evergreens like junipers, spruces, or (some) pines. Avoid holly and other broadleaf evergreens as they are particularly susceptible to desiccation and cold damage during a long winter.
- No matter what you pick, do your best to situate your planters in a sheltered location. Wind and sun have a profound drying effect on evergreens in the winter (more on that here and here). If you do end up using broadleaf evergreens like boxwood, this is especially important.
- Speaking of planters, purchase planters that are as large as possible. This allows for more soil volume; the more soil there is, the better insulated the roots are. This also gives the planter a greater capacity for water and more room for the plant to grow should it survive.
- Avoid using clay, ceramic, or low-grade plastic pots — these will likely crack over the winter. Ensure the planters you use have drainage holes in the bottom.
- Consider adding a layer of Styrofoam insulation along the inside wall of each planter to further protect the roots from the cold.
- Ensure the evergreens stay well-watered in late November and early December, especially if the weather remains mild. Don’t be afraid to give them water in the winter if the soil appears dry or if we have a thawing period.
- If you don’t plan on keeping the evergreens on your porch all winter, consider heeling them into the ground – pot and all – until spring. It’s not as ideal as actually planting them directly in the ground, but it’s better than nothing! This might not be possible if the ground is completely frozen by Christmas. Alternatively, you can move the pots into an unheated garage or shed (ensure it will still receive some light by putting it near a window). Don’t forget to water them on occasion!
Don’t Bring Them Inside
Many people muse about the possibility of bringing their evergreens inside and treating them like an indoor plant for the winter. Though theoretically possible, this has an even slimmer chance of success than leaving them outside. Evergreens rely on a period of cool weather to stay dormant and grow properly. Indoors it is far too warm for them, and the end result is almost always needle drop and eventual death.
Cross Your Fingers!
The unfortunate reality is that you could follow every direction we’ve given and still end up with dead plants in the spring – winter is a fickle and unpredictable season! However, these guidelines will give you the best chance for success. Good luck, and tell us how you do!
Thinking of burlapping your evergreens for the winter? Read our recent blog post on this topic a read through before you do!