The right moment
When the first frost is forecast, it's time to bring the geraniums indoors. They may survive a day or two in slightly subzero temperatures, but once they've been hit by a serious frost, they won't survive the winter. So, play it safe and bring the plants into their winter quarters a few days early.
How it works
There are several ways to overwinter geraniums: completely in a flower box, in clay pots, or bare-rooted in a plastic bag hung upside down. Before storing, the geraniums should be cut back by about 1/3, so that they are about 15 centimeters tall. This pruning will encourage denser growth the following year. Two to three nodes per side shoot should be left. All leaves should also be removed, as these are susceptible to pest infestation.
To overwinter in a plastic bag, the soil-removed root ball is placed in a plastic bag and tied gently. Small holes are poked into the bag to allow some air to reach the ball. Since the plastic bag retains moisture, you don't have to worry about watering with this method. The whole thing is then hung upside down in the garage or basement.
As evergreen plants, geraniums need light even in winter. They thrive at temperatures between 10 and 15 degrees Celsius (50 to 59 degrees Fahrenheit) with natural light—preferably near a bright window facing south or west. Be sure to protect the plants from heat and drafts! The higher the temperature, the more light the plant needs. Conversely, of course, the colder the location, the less light the plants need. Therefore, stairwells or sheds with sufficient daylight are particularly suitable.
