A Weekly Column about Plants, Gardens, & Yards
ISU Extension and Outreach Consumer Horticulture • Lyon-O’Brien-Osceola-Sioux Counties
Overwintering Garden Geraniums
By: Margaret Murphy, Horticulture Educator/Regional Foods Coordinator
Lyon, O’Brien, Osceola and Sioux Counties
It’s that time of year again when gardeners are busy cleaning-up flower beds and vegetable gardens as they prepare them for a good winter’s rest. With the threat of a killing frost looming in our future, we are also faced with the decision to either overwinter our potted plants or send them to the compost. I still have many containers filled with coleus, ornamental spikes, begonias and mums. I also have several pots of garden geraniums. The geraniums were particularly outstanding this year. Even now they continue to present a beautiful display of blooms on the steps of our front porch. I started these geraniums from seed last winter. When you grow something from a seed, tend it over many months, and enjoy its splendor all season long, it’s just not that easy to watch it perish with the first hard frost. So, I think I will try to overwinter my geraniums.
Iowa State University Extension and Outreach has a nice publication that describes three ways you can keep your geraniums through the winter indoors. The first method is to leave them as actively growing plants. Before a hard frost, carefully dig up geraniums in beds or borders and place them in a proper sized pot. For geraniums already in a container, just bring them indoors but always check first for any unwanted hitchhikers. Trim the plants back by one-third to one-half, water thoroughly and set in a sunny spot. If you lack space near a bright window, you can also keep your geraniums under fluorescent light, or use a combination of both natural and artificial light. Also, keep the geraniums away from heat vents or the fireplace as they fare much better in cooler temperatures (60 to 70 degrees F). If your plants start looking spindly or sickly, they may be too warm or suffering from insufficient light. Water your indoor geraniums as needed.
A second way to save your favorite geraniums is to take cuttings. This method works especially well if you have limited space and can’t overwinter large pots. Use a sharp knife and cut a 3 to 4 inch stem from the terminal end or tip of the shoot. Pinch off the lower leaves and dip the cut end in a rooting hormone. Rooting hormone mixtures are available at most garden centers. Place each cutting in a rooting medium. Coarse sand alone or mixed with sphagnum peat moss will work as will vermiculite or a mixture of perlite and peat moss. You can also buy a commercial rooting mix. Water the medium well and let it drain (make sure the container you use has drainage holes). Keep the cuttings just moist enough to prevent them from shriveling. Set them in a brightly lit area but not in direct sunlight as this can cook the plants. Many gardeners will create a mini-greenhouse for cuttings by placing them under a clear, plastic bag while they’re developing roots. Cuttings should be well-rooted after about 6 weeks. Once rooted transplant each cutting to a container of its own using potting soil and keep in a sunny place or under fluorescent light just like you would for the previously mentioned potted geraniums.
The last method for overwintering geraniums is one my mom’s grandmother practiced. This method entails digging up the plants (before a hard frost) and then gently shaking the soil from the roots. The plants were then stored, hung upside down in a cool (45° to 55°F), dry location. In those years, most folks had fruit cellars, which worked well as a place to store dormant geraniums. The temperature stayed cool and it wasn’t too dry. Today, an unheated room, cool basement or garage may work. You can also store the plants in a large, paper bag if you don’t have a suitable place to hang them. Keep the bag open to allow for good air circulation. Don’t be surprised when the leaves start to dry up and fall off. This is probably going to happen.
In mid-March, cut back each plant to about one-third of its original height or to firm, green, live tissue and remove any dead or withered material. Pot up each plant and water thoroughly. Place the potted geraniums in a brightly lit spot and keep your fingers crossed. Plants overwintered in this manner may take awhile before they begin growing again. Keep the potted geraniums indoors until the threat of frost has passed. Then plant outdoors or show them off in a sunlit container garden.
With whatever method you try, always remember to select only healthy plants to overwinter. This will give you the best chance for success with your geraniums next year. For more information of growing geraniums, take a look at the Iowa State University Extension and Outreach publication Growing and Overwintering Garden Geraniums (publication no. RG 320, revised March 2013). For any questions feel free to contact Horticulture Educator, Margaret Murphy, at firstname.lastname@example.org or your local County Extension office.
Contact information: Margaret Murphy 712 472-2576(office) •605 521-7893(cell) •email@example.com