The short answer: It depends on the plant and the container.
When temperatures start to drop, avid gardeners will start the process of preparing their garden and plants for winter. Whether you’re new to caring for plants or simply curious about how to care for your plants when it gets cold, you may wonder if you need to bring your planters inside or if the cold weather will damage them. flower planters
American Meadows’ Tabar Gifford says what to do with your containers and when depends on what you’ve planted.
“The question of what to do with the containers when the snowflakes begin, and frost threatens is a common yearly task for me and many gardeners,” Gifford tells Southern Living.
Gifford explains that there are some considerations about what plants and container types are most at risk and which should be brought inside. There are several common ways to overwinter container planted plants that you want to enjoy again next year and for years to come.
“In general, it’s a wise idea to focus on plants that have a cold hardiness of two hardiness zones colder than your growing zone for best success,” she says. “For example, if you live in a zone six and want to keep your plants in containers over the winter, pick plants that are rated to zone four cold hardiness.”
Gifford adds, “Choosing the best method for you will be based on your personal preferences and factors such as space, access and physical ability.”
Gifford says that in some cases, freezing temperatures can damage your planters.
“If your planters are outdoors and unprotected, they are the most susceptible to damage from freezing temperatures. In short, yes, freezing temperatures can damage some types of planters,” she says.
Terracotta and ceramic pots can crack due to water absorption.
“Think of this danger as you would similar to how frost heaves appear in the roads during winter weather,” Gifford explains. “When the wet soil or snow freezes it can expand and cause containers to crack or break apart. Terracotta and ceramic pots don’t have much ‘give’ to them and are most likely to be damaged in these conditions.”
Plastic pots are less likely to crack as there is some ability for plastics to expand and contract more, but they can become brittle in extreme cold.
“This can shorten their lifespan and cause them to degrade more quickly,” Gifford says.
Concrete and metal planters are typically freeze-resistant and would be considered the most durable to be overwintered.
“However, even these types of containers can experience surface damage over time,” Gifford says. “To avoid damage to your outdoor containers, you can choose to use frost-proof pots or add a layer of insulation, like burlap or old towels and blankets, around vulnerable containers. The other common option would be to move containers indoors to an unheated shed or garage, which greatly reduces the likelihood of damage, though does not completely eliminate it.”
Plants that go dormant (both herbaceous and woody perennials) can be kept in containers over the winter months with some extra care. The most common and typically most safe method is to simply move the containers indoors to a basement, cold frame, unheated garage or garden shed.
“This works great if you have access to such a space and the containers you have are a manageable size to be moved,” Gifford says. “It’s important to note that if you’re moving containers indoors, they will not be getting any natural water over the winter months from snow or precipitation. For this reason, it’s important to give your plants some supplemental water over the winter months.”
Gifford says it’s important not to fertilize your plants.
“You don’t want to wake up the plants, simply water occasionally to keep them alive in their dormant state,” she says.
Another common approach is to gather your containers into an area grouped together. This helps to insulate them more when they are huddled together and protect them from the elements.
“If you can do this in a corner where they are more protected from the elements that’s even better,” Gifford says. “If you’ve got an area that serves as a microclimate, (that is) more protected from wind that’s a great option. Just be cautious of gathering your pots anywhere you might have excessive water exposure or runoff when there’s winter precipitation or snowmelts.”
Gifford says you can also cover or insulate your outdoor containers with materials like burlap, frost blankets, plastic sheeting or tarps, or even old towels.
“You can also use the fall leaves to pack around containers for extra natural insulation or materials like straw bales to build a ‘nest’ to help insulate,” she says. “This will help protect the containers from the freezing temperatures. For larger containers or built-in planters that can’t be easily moved, protecting these with coverings is a good option.”
Another method some gardeners use is to dig a hole and sink the container into the ground.
“This helps to insulate the containers and gives the plants the same cold hardiness environment as your in-ground plants,” Gifford says.
Gifford says that in general, hardy perennials can be kept outdoors in containers during freezing temperatures.
“When choosing plants for your containers that you intend to stay there over the winter, select plants that are zoned for at least one–ideally two–hardiness zones colder than your region to ensure they will survive in pots over the winter,” she explains.
Evergreens, perennials and herbs are the best options to overwinter in containers with the above guidelines.
The low temperature a plant can withstand depends on what you’ve planted, and its lifecycle.
“For example, tender annuals, or tropical plants are particularly vulnerable and can experience damage when nighttime temperatures start dipping below 40 degrees Fahrenheit. For frost-sensitive plants, 32 degrees Fahrenheit (0°C) is the danger point when your plants are very likely to die.”
Gifford says if you’re growing tender annuals or tropical plants, you will want to either bring them indoors before temperatures drop that low.
“For example, I will lift my container- planted dahlias, gladiolus, canna, and calla lilies to prepare for storage when the first frost comes. For others like my edible herbs and plants with tender foliage–begonias and coleus in particular–I’ll bring indoors to continue enjoying throughout the frosty winter months.”
Gifford says that hardy perennials and some shrubs can tolerate even lower temperatures – below the freezing point–but it’s important to know that when grown in planter containers, they are more susceptible to the cold than plants directly in the ground. Plants that are directly in the ground are protected more from early cold spells as the ground takes much longer to cool down and freeze than containers do.
white flower pot “Think of it this way, in the ground, plants are protected by a large mass of soil that takes a while to cool down–like a lake or large body of water–and the cold exposure is coming from just one side: the air above. But when plants are in a container, the cold exposure is coming from all around–the air above, on all sides, and in some cases such as on a deck or balcony, also from below). This causes the containers to cool down and freeze much more quickly than the soil in your garden beds does. You’ve probably seen signs that say ‘bridges freeze before roads’–it’s the same principle. The more exposed an area is to the freezing air temperatures, the more quickly it will freeze. In the case of plants in containers this means they are less protected than in ground plants.”