You can leave pots, flower boxes and other plant containers outdoors over the winter, but they’re often in poor condition come spring. Source: Toño, archivo.infojardin.com
In colder regions of the Northern Hemisphere, the flowering season is either over for the season or coming to an end. But there are still few things to do in the garden …and one of them is to prepare your pots and planters for the winter.
And they’re a mixed bag. Depending on their makeup, some need to spend the winter indoors, others are all right outdoors … under certain conditions and others really can withstand the worst winter conditions.
That’s because some materials used to make pots are simply not able to withstand cold temperatures and have to overwinter indoors. Others are made of frost-resistant materials …but the soil they contain expands and this can cause them to crack, so you have to empty them for the winter. Only a few types of pots are tough enough to spend the winter outdoors full of soil, year after year.
Knowing which is which, you can give yours the maintenance they require, avoiding expensive replacement costs.
The Most Fragile Pots
The most fragile cold pots are undoubtedly those made of clay (terracotta). This product is permeable, so the spaces between its particles fill with moisture during use. When this water freezes and expands, the pot can easily crack, whether emptied of its contents or not. Sometimes the pot will survive a first winter, but rarely two. And terracotta has become quite expensive! So, terracotta pots really should spend the winter indoors or in some other frost-free spot.
Ceramic pots are clay pots, but with glazing. They are often glazed on the outside, but not on the inside. Or it’s the bottom that isn’t glazed. That means they’ll absorb water and crack when they freeze. Plus, ceramic has no capacity for expansion and will likely crack as the soil it contains freezes and expands. Ceramic being even more brittle than terracotta, the slightest crack can quickly split the pot in two. Definitely move ceramic containers indoors for the winter!
You can sometimes find styrofoam pots. Their low price is a big draw and their light weight makes them easy to move. On the other hand, they’re generally not designed for cold climates and become brittle in very cold weather. They should be brought indoors for the winter or at least placed in a lightly heated garage where they won’t undergo the worst of winter cold.
Pots That Take Winter Cold… To a Certain Degree
The following pots can spend the winter outside, but do be forewarned that their longevity will be affected, especially in the long term.
Plastic pots don’t absorb water, but can, depending on their quality (some are more resistant than others), suffer damage when the moist soil they contain freezes and expands. However, the real culprit is not usually the cold per se, although they may be more breakable when frozen, but sun exposure. The sun’s ultraviolet rays cause plastic to become more fragile and less elastic. Often, they become discolored too. After 2 or 3 years outdoors, they therefore tend to become brittle. By bringing them for the winter and thus giving them several months of protection from ultraviolet rays each year, you can help prolong their useful life.
Metal pots (zinc, cast iron, galvanized steel, etc.) are very resistant to frost and can be left outside all winter. Some, however, can rust or oxidize over time. In this case, by emptying them of their contents and bringing them in for the winter, you can reduce the speed of this degradation. For maximum durability, clean them well in the fall and rub them with a cloth soaked in oil. The oil will help protect against rust and oxidation.
Wood is resistant to freezing soil because it has a certain natural elasticity. On the other hand, the repeated action of freezing and thawing potting soil can weaken the container’s joints. So, it’s best to remove at least half of the potting soil if you leave them outdoors for the winter: that will reduce the pressure from the freezing potting mix.
Also, all types of wood (even so-called “water-resistant” wood) will rot over time in contact with moist potting soil. For a maximum longevity, therefore, it would still be wise to empty them of their contents every winter and keep them dry. However, since cold per se is not a factor, you don’t have to bring them into your home or a heated storage area: a tool shed or unheated garage would be fine.
In addition, since you’re emptying them of their contents anyway, why not coat the inside of any wooden container with some sort of waterproofing product every 3 or 4 years. You could use linseed oil or boat varnish, for example. That way, you’ll extend the container’s useful life by many years.
Concrete is very frost resistant …when it’s dry. Even moist, it’s a pretty tough product. However, when a concrete pot contains moist potting soil, expansion can still cause it to crack. The problem is that concrete pots are heavy and difficult to move: bringing them indoors or into a heated garage for the winter takes quite an effort. The most logical option is to leave them outdoors, but to empty them of at least half their soil for the winter.
Pots You Can Leave Outdoors Without Problem
Smart Pots and other containers with soft, aerated sides tolerate winter outdoors very well. Their flexible walls adapt perfectly to the expansion and contraction of freezing and thawing soil and the fabric used is very resistant to ultraviolet rays. Or at least those labeled as UV resistant are. Beware of lower quality rip-offs that make no such claims.
Fiberglass and resin pots are relatively new on the market. As with plastic, they can be molded into all possible forms and they can take on an infinite number of finishes and colors, easily imitating concrete, stone, lead, etc. But they cost more than plastic … a lot more! They resist the worst winter cold without cracking and are, in many situations, the laidback gardeners’ best choice for outdoor gardening.
There you go! A little care now could help your pots, planters and flower boxes last a lot longer.