It’s time to think about how to close our gardens down for the winter, and part of that might be how do we take care of plants in containers and help them to survive through the winter. Any plants that are considered tender annuals or tropical plants should be brought indoors if you wish to overwinter them.
Perennials and shrubs that are grown in the ground have the insulating benefits of the soil that they are planted in, which helps to regulate temperatures and protects the root systems from freezing.
Plants in containers don’t benefit from that — research has shown that the soil in an above-ground container can match the surrounding air temperature.
If the surrounding air temperature is five degrees below zero, then the soil in the container will be the same. Temperatures that low can damage and kill the root systems of plants.
With a few simple steps we can minimize the temperature fluctuations and help prevent the root systems from freezing. If possible, dig a hole and sink the containers down into the ground.
If this isn’t possible, consider insulating the pots by surrounding them with bubble wrap and burlap or 2-inch-thick Styrofoam.
Plants also can benefit by being clustered together in a corner and adding a layer of mulch or straw over and around the containers. Another option includes storing them in an unheated garage or building.
Before putting any container plant to rest for the winter, make sure that the containers are well watered and that the plants are dormant. Throughout the winter, make sure to check on the containers and water as needed to keep the soil moist.
Any containers that you are overwintering outdoors that contain broadleaf or needled evergreens such as boxwoods and hollies also need to have the soil moisture monitored and water as needed to prevent the soil from drying out.
If you are planning on overwintering plants outdoors, make sure to consider what the containers are made of. Containers made of wood or plastic can survive winter temperatures with potting mix and plants still in them.
Containers made of terracotta, which is porous, can hold moisture and the freezing and thawing temperatures can cause the container to easily crack over the winter, and it’s not recommended to overwinter plants in these types of containers.
From personal experience, plastic containers, depending on the quality, over time can eventually break down from staying outdoors, and as with any container, make sure to inspect it for cracks or damage each year and replace as needed.
With just a few simple supplies and a bit of planning, you can have plants that survive year after year in containers outdoors.