Unless you live where the winters are mild, those pretty zonal geraniums in your garden will succumb to the first frost of the season. But they don’t have to; it’s easy to overwinter them until next spring.
Zonal geraniums, or pelargoniums, are not true geraniums, but are called “zonal” because of the markings on their leaves. They are usually grown as annuals. (Perennial cranesbills are the so-called true geraniums. They take their name from the shape of their long, beak-like seedpods.)
Try one of these simple methods to hold your zonal geraniums over the winter.
Make cuttings. Make 3-4” cuttings from your plants, removing any flowers or buds, and removing all but three leaves on each cutting. Put the cuttings in a glass of water in a sunny window, and watch for roots to form. Replenish the water as needed. Once good roots have formed, pot the cuttings in small containers of fresh potting mix. Water sparingly, and don’t fertilize. After all chance of frost has passed, acclimatize them to the outdoors by gradually increasing their exposure to sunlight and outdoor temperatures. After a couple of weeks, they should be ready to transplant into the garden or into bigger pots.
Keep them as houseplants. If your geraniums aren’t already in containers, dig them up, cut back the tops and plant them in pots. Use fresh potting mix and pots that are clean and pest-free. The plants will need bright light, so keep them in a sunroom, south-facing window, or under fluorescent lights. For best results, give them daytime temperatures around 65 to 70 degrees F., and nighttime temperatures around 55 degrees F.
Store the bare roots. You can also dig up your geraniums, remove the dirt from their roots and bring them inside. Hang them upside down in a dark basement or other location where the temperature stays 45 to 50 degrees F. The plants will go dormant until spring. If you can’t get all the dirt off the roots, put the plants upside down in a paper bag and hang the bag. It will catch any dirt that continues to dry and fall off. Be sure to make some holes or slits in the bag for ventilation.
Store them in a box. Again, dig up your geraniums and remove as much dirt as you can. Remove any dead, moldy, or diseased leaves and stems. Let any green leaves and stems remain on the plants. Put the plants upside down in a cardboard box, and close the lid, leaving it loose enough to allow for air circulation. Put the box on a shelf and keep it in a basement or other dry, dark, cool spot.
Open the box every couple of weeks to check your geraniums. If you see mold or other problems, discard those plants. When the geraniums start looking dehydrated and shriveled, usually in 2 or 3 months, take them out of the box. Cut back the brown stems until you see some green. Then plant the roots in coarse, slightly moist potting soil. Gently tamp the soil down. Wait for new leaves to form, usually in 4 to 6 weeks, before you begin watering. Allow the top of the soil to dry out before you water again, and feed with a diluted (about one-quarter strength) liquid fertilizer.
Again, gradually expose your revived plants to the sun and warm temperatures when you move them outside. When new growth appears, you’ll know you’ve saved money and successfully overwintered your beautiful flowers.
Don’t want to overwinter? Grow a cold-hardy perennial geranium.
‘Rozanne’ cranesbill is a perennial, semi-evergreen geranium. Give it partial to full sun and regular water. Blooms appear from early spring to summer. The delicate, violet-blue flowers are surrounded by chartreuse foliage. Try ‘Rozanne’ as a groundover, in a rock garden, or in a mixed bed. This cranesbill thrives in USA zones 4 to 9.