Understanding Whether to Introduce Potted Plants in Cold Climates
When chilly weather approaches, passionate gardeners commence the process of safeguarding their gardens and plants for winter. Regardless of whether you're a novice in taking care of plants or simply intrigued about how to care for your plants during the cold season, you might be curious if you need to move your planters indoors or if the cold weather will cause harm.
American Meadows' Tabar Gifford suggests that the course of action for your containers 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 annual task for me and many gardeners," Gifford tells Southern Living.
Gifford elaborates that there are several factors to consider, such as the plants' and container's resilience to the cold. There are various methods to overwinter container-planted plants to enjoy them again the following year and for years to come.
"In general, it's a smart idea to focus on plants that have a cold hardiness of two hardiness zones colder than your growing zone for the best results," she says. "For example, if you live in a zone six, and want to keep your plants in containers during the winter, choose plants that are rated to zone four cold hardiness."
Gifford also suggests that the method you'll use depends on your personal preferences and factors such as space, access, and physical ability.
Will Freezing Temperatures Damage Planters?
Gifford points out that some types of planters may be susceptible to damage by freezing temperatures if they're left outside and unprotected.
"If your planters are outdoors and unprotected, they're most vulnerable to damage from freezing temperatures," she says. "In short, yes, freezing temperatures can damage certain types of planters."
Terracotta and Ceramic Pots
Terracotta and ceramic pots can crack due to water absorption. Gifford compares this danger to how frost heaves appear on the roads during winter weather.
"When the wet soil or snow freezes, it can expand and cause containers to crack or break apart," Gifford explains. "Terracotta and ceramic pots aren't very flexible, and they're most likely to be damaged in those conditions."
Plastic Pots
Plastic pots are less likely to crack as they can expand and contract more, but they can become brittle in extreme cold.
"This can shorten their lifespan and cause them to degenerate more quickly," Gifford says.
Concrete and Metal Planters
Concrete and metal planters are typically freeze-resistant and are among the most durable options for overwintering.
"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 alternative option would be to move containers indoors to an unheated shed or garage, which significantly reduces the likelihood of damage, though it doesn't completely eliminate it."
Do Planters Need to be Brought Inside During Freezing Temperatures?
Plants that go dormant, both herbaceous and woody perennials, can be kept in containers over the winter months with some additional care. The most common and typically safest 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 are manageable in size to be moved," Gifford says. "It's important to note that if you're moving containers indoors, they will not get any natural water from snow or precipitation during the winter months. For this reason, it's important to give your plants some supplemental water during the winter months."
Gifford also recommends not fertilizing your plants during this time.
"You don't want to wake the plants up; simply water occasionally to keep them alive in their dormant state," she says.
Another common method is to gather your containers in one area. This helps insulate them more, as they're huddled together and protect them from the elements.
"If you can do this in a corner that's more protected from the elements, that's even better," Gifford says. "If you've got an area that serves as a microclimate, which 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 during winter precipitation or snowmelt."
Gifford suggests covering or insulating 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 them with coverings is a good option."
Another method that some gardeners use is to dig a hole and sink the container into the ground.
"This helps insulate the containers and gives the plants the same cold hardiness environment as your in-ground plants," Gifford says.
When selecting plants for winter-resistant containers, opt for those rated for at least one, ideally two, zones colder than your local climate to ensure their survival.
Evergreens, perennials, and herbs are ideal choices for overwintering in containers following these guidelines.
What Temperature Is Too Chilly for Pottered Plants?
The tolerance level for cold temperatures varies depending on the plant species and its lifecycle.
"Tender annuals or tropical plants, for instance, are highly susceptible and can suffer damage once nighttime temperatures dip below 40 degrees Fahrenheit (4.4°C). For frost-sensitive plants, the critical point is 32 degrees Fahrenheit (0°C), where they become extremely vulnerable and are at a high risk of expiring."
According to Gifford, if you're cultivating tender annuals or tropical plants, you should consider moving them indoors before temperatures drop to such low levels.
"To prepare for storage, I lift my container-planted dahlias, gladiolus, canna, and calla lilies once the first frost arrives. When it comes to edible herbs and plants with delicate foliage, like begonias and coleus, I'll bring them indoors to continue their growth during the winter's frosty months."
Gifford points out that hardy perennials and certain shrubs can withstand even lower temperatures, but they remain more vulnerable in planter containers since they are exposed to the cold from all directions - the air above, on all sides, and, in some situations, even from beneath, for instance, on decks or balconies. Plants directly in the ground have a more extended protection from early cold spells due to the ground's slower cooling down and freezing pace.
"Consider this analogy: plants in the ground are sheltered by a significant mass of soil that requires a while to chill down, similar to a lake or sizeable body of water, and the frost exposure originates solely from the air above. On the other hand, when plants are in a container, they experience frost exposure from all sides, including the air above, on all sides, and in some instances, from the bottom, which causes them to chill and freeze more rapidly than soil in garden beds does. You've likely encountered warnings saying 'bridges freeze before roads' - the concept parallels this, implying that the more exposed an area is to cold air temperatures, the quicker it will freeze. As such, plants in containers are less safeguarded than plants in the ground."
- To ensure the survival of your container-planted plants during winter, Gifford recommendsFocusing on plants with a cold hardiness rating of two hardiness zones colder than your growing zone.
- If you're considering container gardening for seasonal plants, it's essential to consider the resilience of both the plants and the containers to freezing temperatures.
- When planning your gardening landscaping ideas, consider using freeze-resistant materials like concrete or metal planters to protect your plants from damage during cold weather.
