Overwintering Containers in Cold Winter Climates
As autumn fades and Old Man Winter begins to knock at the garden gate, give your containers—and their frost-tender contents—specific care to help them survive.
Choose the right containers. When you opt to include outdoor container gardens in your planting plan, select the container carefully. Terra-cotta and ceramic pots absorb moisture, which expands as it freezes and cracks the container. Metal, concrete and wood containers typically handle freezes well, as do fiberglass and resin pots. Some plastic pots also survive winter fine, but may become brittle over time. Winter sunlight can fade fiberglass and resin pots.
Coddle those pots. Many manufacturers suggest emptying containers, flipping them upside down, and elevating them on narrow boards or bricks for winter. Others suggest moving pots into an unheated shed or garage. For heavy containers that cannot be moved, fill the container to the brim with soil or compost to prevent water collection, which can freeze, expand, and crack the container rim. Some gardeners also cover the top of the filled pot with a 3- to 4-inch layer of straw, held in place with burlap tied around the container.
Shift plants. To ensure plant survival in containers through winter, select plants hardy to two zones lower than yours. Alternatively, lift plants from containers for winter and tuck them into soil in a planting bed, vegetable garden, or near a compost bin. Soil insulates roots and helps plants survive winter. Tuck plants into soil 1 to 2 inches deeper than they normally sit in a container. Return the plants to containers in spring.
Mulch mums. In the northern third of the country, garden mums planted in fall most likely won’t survive winter even if you transfer them to in-ground beds. Improve their odds by skipping the pots altogether and tucking them into soil at the start of fall. Mums are shallow-rooted, and winter’s freeze-thaw cycles can push plants out of soil, exposing roots. Help prevent this by covering plants after the ground freezes with loose mulch that permits water and air flow. Materials such as chopped autumn leaves or straw work well. Cover the plant entirely with a layer up to 8 inches deep.
Protect tropicals. Tender tropical plants have varying degrees of cold tolerance. Plants such as Clerodendrum ugandense (blue butterflies) need protection when temperatures dip below 45° F. Staghorn ferns survive to 35° F. Most non-hardy fuchsias should be brought indoors when temperatures tumble below 30° F. Research specific cold tolerances for your favorite tropicals.
Overwinter tropical plants indoors in a cool room with light from a window. Barely water plants through winter. The goal is to keep roots alive; if leaves drop and stems become bare, don’t fret. They’ll leaf out in spring when you add a little compost to the soil and fertilize.