Flowering is essentially over for the season… at least outdoors! But there are still a few things to do in the garden… and one of them is to prepare pots and planters for winter. Depending on their composition, some have to go inside for the winter, others can spend the winter outside under certain conditions, and others can withstand our winters.
In fact, some of the materials used to make pots are not at all frost-resistant, so they have to be put away for the winter. Others are frost-resistant… but the soil they contain expands and can cause them to burst. They must therefore be emptied of soil for the winter. Only a few types of pots are hardy enough to spend the winter outdoors filled with soil, year after year. By knowing which is which, you can give them the maintenance they need, avoiding costly replacement.
The Most Fragile Pots
The pots most sensitive to cold are undoubtedly those made of terracotta. This product is permeable to water, so the interstices between the particles fill with moisture during use. When this water freezes, the pot can easily burst, whether or not it is emptied of its contents. Sometimes a pot will survive a first winter, but rarely two. Terracotta pots must therefore spend the winter indoors or in another frost-free location.
Ceramic pots are often glazed on the outside, but not on the inside. Or sometimes it’s the bottom that’s not glazed. So water can get in and cause them to shatter. Porcelain is even finer and more fragile than terracotta, and the slightest crack quickly results in a pot split in two.
Styrofoam pots are lightweight and easy to move around. However, most were not designed for cold climates and become brittle and fragile in very cold weather. You need to bring them in for the winter, or at least place them in a slightly heated garage where they won’t suffer the worst of winter’s assaults.
Pots that resist… a little
The following pots can overwinter outdoors, but their longevity will be affected, especially over the long term.
Plastic
Plastic pots don’t absorb water, but depending on their quality (some are more resistant than others), they can be damaged by the expansion of the soil they contain. Above all, however, it’s not a question of cold as such, but of age. When pots are exposed to the elements (ultraviolet rays, cold, etc.), they become more fragile and less elastic (some also discolor). After 2 or 3 winters outside, they become brittle. Bringing them inside for the winter will extend their life for many years.
Metal
Metal pots (zinc, cast iron, galvanized steel, etc.) are frost-resistant and can be left outside all winter long. Some, however, can rust over time. In this case, emptying them of their contents and taking them inside for the winter will reduce the rate of decomposition. For maximum durability, clean them thoroughly in autumn and rub them with an oil-soaked cloth. The oil will help protect them from rust.
Wood
Wood itself is frost-resistant, as it has a certain elasticity. However, the repeated freezing and thawing of potting soil can weaken joints. That’s why it’s a good idea to empty them of at least half their potting soil if you’re leaving them outside for the winter, to reduce the pressure of the expanding potting soil. All wood (even so-called “water-resistant” wood) rots over time in contact with damp potting soil. For maximum durability, therefore, it would still be wise to empty them of their contents every winter and keep them dry, but not necessarily indoors (a shed will do). What’s more, as long as you’re emptying them of their soil, every 3 or 4 years, paint the inside of the wooden container with a waterproofing product such as boat varnish. This will extend the life of the container for many years to come.
Concrete
Concrete resists frost very well… when it’s dry. On the other hand, when a concrete pot contains moist potting soil, expansion can cause it to crack. On the other hand, concrete pots are heavy and difficult to move: bringing them in for the winter is quite an effort. The ideal solution is to leave them in place, but empty them of their contents!
Pots that can be left outside without a problem
Fiberglass and resin pots are relatively new on the market. As with plastic, they can be molded into any shape and given an infinite number of finishes. But they are much more expensive than plastic, not least because they are much more durable. They can withstand the worst of winter’s cold without cracking, and are the best pots for outdoor gardening if you don’t want to put them away every year.
And there you have it! A little maintenance now could make your pots, planters and containers last much longer.
Larry Hodgson published thousands of articles and 65 books over the course of his career, in both French and English. His son, Mathieu, has made it his mission to make his father’s writings accessible to the public. This article was originally published in Le Soleil on November 21, 2005.
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