Overwintering Containerized Plants

You have worked hard this growing season to make your home landscape a beautiful and functional place. With winter coming, it is time to protect your containerized plants and your containers themselves to ensure they survive the winter and beautify your home again next spring. To protect outdoor plants and containers, first arm yourself with knowledge. Know your cold-hardiness zone, know the cold-hardiness range of your plants and know the materials that make up your containers.

Knowing your USDA Plant Hardiness Zone is as simple as checking the map (http://planthardiness.ars.usda.gov/PHZMWeb/) and as complicated as understanding your microclimate. The map shows average minimum temperatures and not the lowest temperatures a zone can experience. Use the map, your personal experience, advice from your neighbors and help from Cooperative Extension Master Gardeners to determine the actual zone rating for your home.

Then, find out the zone ratings of your various containerized plants. Look on plant tags, growers’ websites or ask a Master Gardener for help. If your plants are cold hardy to one zone below yours and they are in a large pot made from a material that can withstand winter weather, feel free to leave them outside. Grouping outdoor potted plants together, putting them in an area protected from the wind and placing them close to the house can help them to experience less winter abuse.

If your cold-hardy plants are in a small or thin-walled container, consider moving them to an unheated garage for the winter so fragile plant roots do not get too cold. Plants that are not very cold hardy can be placed in the garage on a wall shared with the house to keep warm, or they can be brought inside. It is helpful to plant less cold-hardy plants in attractive containers that coordinate with your indoor décor so they brighten the home throughout the winter. Whether you overwinter your plants outdoors, in the garage or in the home, water them sparingly so they do not completely dry out.

Once you have taken steps to protect your overwintering plants, protect your pots too. Discovering what your gardening containers are made from is important because planters may expand and crack in cold winter weather. Repeated freezing and thawing can be hard on some materials.  Be especially careful with earthenware, ceramic and terracotta. Concrete, wood, plastic and metal can stand up to winter weather abuse, but plastic and metal also offer little protection for tender plant roots.

Shelter or move indoors plants in containers made of sensitive materials. If your container is not currently housing a plant, it is best to empty the pot before storing it. An old Master Gardener trick is to empty the soil from containers onto a large tarp. Then, mix compost into the pile. Taking this step now will help you feed your soil so it can nurture your plants next spring. Store displaced soil in a trash can on wheels for the winter. In spring, it will be easy on your back to bring out your empty pots, arrange them to your liking, roll over your soil and fill them up. You will be planting again in no time!