AMES, Iowa – Geraniums are a popular flowering plant for beds, borders, containers, hanging baskets and window boxes. The first hard frost will destroy geraniums, unless gardeners take steps to over-winter them. Horticulturalists with Iowa State University Extension and Outreach tell how to over-winter geraniums indoors. To have additional plant and garden questions answered, contact the ISU Hortline at 515-294-3108 or firstname.lastname@example.org.
Geraniums can be over-wintered indoors by potting up individual plants, taking cuttings or storing bare-root plants in a cool, dry location. Remove plants from the garden (or take cuttings) prior to the first fall frost.
Using a sharp knife, take 3- to 4-inch stem cuttings from the terminal ends of the shoots. Pinch off the lower leaves, then dip the base of each cutting in a rooting hormone. Stick the cuttings into a rooting medium of vermiculite or a mixture of perlite and sphagnum peat moss. Pots and flats with drainage holes in the bottom are suitable rooting containers. Insert the cuttings into the medium just far enough to be self-supporting. After all the cuttings are inserted, water the rooting medium. Allow the medium to drain for a few minutes, then place a clear plastic bag or dome over the cuttings to prevent the foliage from wilting. Finally, place the cuttings in bright light, but not direct sunlight. The cuttings should root in six to eight weeks. When the cuttings have good root systems, remove them from the rooting medium and plant each rooted cutting in its own container. Place the potted plants in a sunny window or under artificial lighting until spring.
Carefully dig up each plant before the first fall frost and place in a large container. Water each plant thoroughly. Bring the geraniums indoors and place the plants in a sunny window or under artificial lighting. Geraniums prefer cool indoor temperatures. Daytime temperatures of 65 to 70 degrees Fahrenheit and slightly cooler night temperatures are ideal. During their stay indoors, water plants when the soil surface becomes dry to the touch. Geraniums are likely to become tall and lanky by late winter. Prune tall, lanky plants back in March. Cut the geraniums back by one-half to two-thirds. The geraniums will begin to grow again within a few days and should develop into stocky, well-branched specimens by May.
Carefully dig up the geraniums before the first fall frost. Shake the soil from the plant’s roots. Then place one or two plants in a large paper sack and store in a cool (45 to 55 degree Fahrenheit), dry location. An unheated bedroom or indoor porch might be a suitable location. An alternate (somewhat messier) method is to hang the plants upside down in a cool, dry location. The foliage and the shoot tips will eventually die. In March, prune or cut back each plant. Remove all shriveled, dead material. Prune back to firm, green, live stem tissue. After pruning, pot up the plants and water thoroughly. Place the potted geraniums in a sunny window or under artificial lighting. Geraniums that are pruned and potted in March should develop into good-sized plants that can be planted outdoors in May.