Perennials in Containers

by Shannon Moreau | Fort Collins Nursery

Annuals are a staple for container gardening, so why don’t perennials get the same attention? The answer lies in the unique conditions created by container living. While perennials may seem like an easy way to plant a patio pot once and enjoy it for years to come, they are not a plant-and-forget solution. However, with careful planning, there are a few different ways to use perennials in containers. 

It’s fun to experiment with containerized perennials. They provide a chance to try different plants that would be difficult to grow in the landscape. This is also a great option for gardening in spaces that do not have an in-ground garden. The principle of “fillers,” “spillers,” and “thrillers” should still be used to add dimension and interest to your designs. While some may choose to treat perennials as annuals and toss them in the compost each year, another option is to use these hardy plants in your pots through the growing season, then plant them into your landscape in the late summer or early fall. If you do not have a space to plant them, share your plants with neighbors, friends, or family members.

When selecting your pots, choose containers that are at least 14” in diameter. Choose materials that are frost-resistant, such as plastic or glazed ceramic. Next, determine what soil will be best for your perennial plants. For the majority of plants, an all-purpose, well-draining potting soil works nicely. Avoid using heavy planting media that includes topsoil or is heavily amended with compost, as these products tend to drain poorly. During the summer months, the containers will need routine irrigation to keep the plants from drying out, but will suffer if constantly waterlogged.

To overwinter your perennials in containers, you’ll need to adjust how you care for them compared to those growing in the landscape. While a large container helps insulate your plants’ roots, they will not get the same degree of protection as those growing in the ground. For the best chance at success, select plants that can handle two zones lower than your local hardiness zone. For example, if your local hardiness zone is 5, choose plants that are zone 3 as they will withstand temperatures of -40° Fahrenheit. To further enhance a stable soil temperature, move your containers into a shaded location, an unheated garage, a cold frame, or a shed in late fall or early winter. The consistently low temperatures in these locations will keep the soil in your container at a steady temperature and allow for uniform moisture. When containers are left in a sunny location, the soil undergoes a freeze and thaw cycle, which can damage roots over the winter months.  Plan on watering once or twice a month during the winter on days that are above 40 Degrees fahrenheit. 

Finally, be prepared for a bit of trial and error. Every situation is unique, so you might have to try a few different plants to find the best ones for your containers. After all, the best gardeners in the world have killed more plants than anyone else!