How to Overwinter Tender Perennials and Annuals

After investing hours weeding, watering and fertilizing plants and flowers during the summer, it can be difficult to see them wilt away after the first hard frost. There are ways of keeping some tender perennials and annuals surviving and thriving through the winter months to be repotted in the spring. Here are a few strategies for over-wintering certain plants and flowers.

Overwintering Tender Perennials

Perennials are plants that die back when the weather turns cold then bloom and grow again in the spring. In most cases, perennials can survive the winter but some tender plants typically cannot. These plants include Canna, Dahlias and Gladiolas. Their underground organs (i.e. rhizomes, tubers or corms) should be dug up just after the first frost and kept during the winter.

• Canna offer bright, torch like flowers and large banana like leaves. Some varieties can grow quite tall (six feet) while others remain dwarf like in size (two to three feet in height). After the first frost and after the leaves have died, the rhizomes can be dug up. Let the rhizomes dry and then store them in open crates or mesh bags at 40 to 50 degrees (‚”Growing and Over-wintering Tender Perennials” published by the Iowa State University Extension, revised January 2005).
• Dahlias come in a thousand cultivated varieties according to ‚”Growing and Over-wintering Tender Perennials” published by the Iowa State University Extension. These bright showy blossoms come in all colors and sizes except blue and brown. After a killing frost, the plants should be cut down and the tubers carefully dug up. The tubers should be washed with water and allowed to dry. Once dry, they can be stored upside down in vermiculite.
• Gladiolus provide rich and varied color as the blooms grow along a slender stalk. These plants develop from a corm (underground stems). At the end of the plant’s flowering or the end of the growing season, the corms should be dug up, allowed to dry and then stored in a mesh bag.

According to the Iowa State University Extension’s Resource Guide for Iowa Master Gardeners (revised September 2007), gardeners should discard any soft or mushy bulbs before planting in the spring.

Potted Annuals

Plants such as Geraniums can be overwintered in a couple of different ways. One way, is to repot the plant in a smaller pot, assuming that it is part of a larger container, and overwintered. The second way is to dig up the Geranium, shake off the dirt and hang the plant upside down in a cool dark place. When the weather gets warm the plant can be placed outside. Typically, these plants will need to be cut back to allow it to re-grow in a bushier state.

Other container plants such as Hibiscus, Begonias and other plants can be potted up and kept inside. These plants will require a sufficient amount of light so it is important to use a grow light or find a sunny spot in the house.

These are a few strategies for overwintering favorite plants. The success of these strategies can be dependent on the correct medium for storage, sufficient light, water and adequate space for placing pots in the house.