Some parts of the state have experienced frost already and most will in the next week, so it’s time to think about overwintering tropical plants. Which plants do we mean? In this post, we’ll cover canna and calla lilies, geraniums (Pelargonium), begonias and coleus. If there are other questions you have about overwintering tropical plants in Minnesota, put them in the comments and we’ll try to answer them in future posts.
Storing plants indoors for the winter to grow next year saves money and it often gives you larger or more plants the following year. Many of these plants can get quite large in their native environments, so letting them grow more than one season allows them to thrive. Some tropical plants are stored indoors as tubers, while others are brought inside in their containers for the winter.
Canna and Calla Lilies
These tall tropical plants add height, fascinating foliage and late-season flowers to the garden. Like dahlias and gladiolus, they grow from an underground structure called a rhizome. Rhizomes function in a similar way to bulbs in that they store food for the plant’s next year. To overwinter canna and calla lilies, pull the plant from the ground or container after the first frost has nipped the leaves. (At this point, the plants don’t look that good, anyway.) Cut the main stems back to 2 to 3 inches.
Brush the dirt off the rhizomes, but don’t wash them. Your goal is to keep the rhizome dry to avoid rotting. If possible, leave the rhizomes outside in a sunny location for a few days to allow the rhizome skin to dry a bit. Then place the rhizomes in a paper bag or a box and store them in a cool, dark place, such as an unfinished basement or a heated garage for the winter. Do not let the bulbs freeze!
In early spring, plant the rhizomes about 3 inches deep in containers with a good potting mix. Bring them into a sunny room, water and watch them grow. Do not plant cannas or callas outside until the weather is warm and nights are reliably in the 50s.
Begonias and Geraniums
Begonias and geraniums offer a couple of options for storage. Tuberous begonias need a winter dormant period and can be prepared and stored in the same way as cannas and callas. Pull the plant from the ground after a frost and cut off all but about 6 inches of stem. Dust off the soil from the tuber at the base of the plant carefully (it helps if the plant is a bit dry), let the tubers dry outside a few days, then pack them loosely in paper bags and store in a dry place indoors. In spring, you can pull them out, plant them up and get them started indoors.
Some begonias—rhizotamous begonias, cane-types (such as Angel Wing) and Rex begonias—can be kept as indoor plants through the winter as they do not require a dormant period. Care can be tricky, but if you have the right light and a bit of humidity, you may be able to enjoy them year-round. Check out tips on overwintering begonias from our friends at Proven Winners.
Geraniums are stored in a similar way to tuberous begonias. Let the plants dry out a bit in their container, cut them back to 6 inches or so of stem, knock off the dirt, then store them wrapped in paper indoors in a dark place. Start them up indoors early in the spring.
Geraniums can also be kept going indoors in the winter. Susan Betz, author of Herbal Houseplants (Cool Springs Press, 2021) recommends growing geraniums in clay pots placed in a south-facing window. The plants need at least 4 hours of direct sun per day and you want to be careful not to overwater them. She prunes plants to keep them from being too leggy. You can also take cuttings from geraniums in fall, root them inside during the winter and expand your stock for next year.
While I have heard of gardeners who have overwintered coleus plants right from their garden, most will take cuttings in fall and create new plants for the next season. This is easy to do and a great way to increase your supply of coleus. It’s also a fun project if you have youngsters at home.
Before first frost (so like, now!), snip off the top 3 to 4 inches of a healthy coleus stem. You can get several cuttings from a plant. Strip off the lower 2 inches or so of leaves, then place the stems in a good soilless potting mix, water well and bring them into a warm but not sunny location indoors. (If you want some extra help getting the plants to root, dip each cut end into rooting hormone before planting in the pot.) You can put many cuttings in a single pot during this stage. The Chicago Botanic Garden recommends covering the cuttings with a plastic bag to hold in the moisture. In a week or so, the cuttings will have little roots and you can re-pot each plant into its own small container. Place them in a sunny window and trim them back regularly to prevent them from getting leggy.
We know northern gardeners are creative about overwintering tropical plants. Tell us your secrets for getting your favorite plants through the winter.