When I was a very young child, my father always overwintered his “zonal geraniums” (actually, they are zonal pelargoniums: [Pelargonium x hortorum]) in the time-honored tradition, by knocking the soil off their roots and hanging them upside down in the root cellar. Then when we, like so many 1960s families, “redid the basement,” putting in a family room, extra bedrooms, etc.. Extra insulation was added and the root cellar, now seen as a source of undesirable cold, moist air, disappeared. After all, who needed a root cellar anymore? We all had refrigerators!
But his pelargoniums didn’t like the change. I can well remember them, now hanging upside down near his workbench, with newspaper spread underneath to catch all the falling leaves. By spring, there was little life left in them and many simply died. Even the best never recovered fully from the shock. He soon stopped overwintering pelargoniums and took up starting new ones from seed. Problem solved.
What Went Wrong?
Gardeners still try the old method, following methods handed down over the generations, and the results can still be pretty pathetic. Sometimes old methods are just great, but other times, they’re simply … wrong!
First, hanging pelargoniums upside down was never a good idea. People used to think it “directed energy from the roots back to the stems,” but nowadays, we know that’s nonsense! There’s no logical reason to turn any plant upside down for extended periods. Nor was knocking all the soil off their roots of any use: that just exposes roots to drying air and usually kills them, forcing the plant, if it survives, to produce new ones. This “upside down exposed roots” thing was just bad horticulture. Essentially, it was plant torture.
Secondly, it must be said that pelargoniums don’t much like being forced into dormancy. It’s simply not a normal state for them. Of course, the zonal pelargonium (P. x hortorum) is a hybrid species and never existed in the wild, but its parent species (P. zonale and P. inquinans, both from South Africa) were small, somewhat succulent shrubs that never went dormant. During dry periods, their growth slowed down, but didn’t stop, and they kept most of their leaves, living off moisture stored in their thick stems.
When forced into full dormancy (when you both withhold water and light from them), zonal geraniums will put up with it if necessary (like any plant, they’ll do their best to try and survive), but they won’t be happy campers.
Our parents and grandparents had better luck keeping pelargoniums dormant than we do because they stored them in root cellars, where it was very cold (usually less than 50˚ F/10˚ C), but above freezing, and where humidity was extremely high: about 90 to 95%. Thus the plants lost little moisture to the air.
In most situations where you could store pelargoniums these days, though, the air is going to be very dry, adding another layer of stress to the plants’ already dire situation. No wonder so many pelargoniums stored this way are so weak come spring they simply die when repotted.
Forcing Dormancy With Less Stress
If you want to force your pelargonium into dormancy, at least do so logically. A garage or cool basement where temperatures remain in the 40 to 50˚ F (5 to 10 ° C) range would be best. And try not to expose the roots to the open air, inevitably very dry. When you dig the plant up in the garden, it’s best to leave the root ball intact and to put it in a paper bag or to wrap it in newspaper to reduce water loss. If the plant was growing in a pot, leave it there, bringing in indoors pot and all. The room can be completely dark, as now the plant will be fully dormant.
During the winter, spray the rootstock or water it lightly once a month so as to maintain a minimum amount of moisture. You’ll still need to spread a newspaper under the plant or put it in a cardboard box to catch its falling leaves, but it won’t likely lose all of them.
Come spring (mid- to late March in many climates), repot the plant and move it in front a sunny window or under plant lights and begin watering again, slowly at first, then more as new growth appears. Start fertilizing as well. By early summer, it should have recuperated and be ready to plant outdoors.
Better Yet, Keep It Growing
The following method of maintaining pelargoniums over the winter has always been the safest and most successful: simply keep it growing in front of a bright window or under lights. This best reproduces the conditions that pelargoniums received in the wild.
With this method, simply clean the plant a little when you bring it indoors, removing dead and yellow leaves and dried flowers. Also, spray the leaves in soapy water (1 teaspoon of insecticidal soap per quart of water (5 ml per litre)) to kill any insects that are trying to hitch a ride indoors and likewise give the roots a 15-minute soak in soapy water for the same reason. If you dug it out of the garden or a container, pot it up. You may also want to pinch the stems tips (i.e. remove the terminal bud) in order to stimulate better branching, as that will give a fuller-looking plant.
Now place the pot at room temperature (anywhere between 40 ˚ F and 80˚ F [5 ˚ C and 25˚ C] will do) in front of the sunniest possible window or under intense artificial lighting, setting it on a saucer to catch any excess water.
Over the winter, water as needed when the soil is dry to the touch. Note that the frequency of watering can vary enormously according to the growing conditions: from as often as once every five days to as little as once every three weeks. (The cooler the room and the greater the air humidity, the less water the plant will need.) Put off fertilizing for a while: “feeding” a pelargonium when the light is low, as it likely will be most of the winter, can lead to it stretching for the light (etiolation). Resume fertilization (with an all-purpose product) in March, when the days begin to seriously lengthen.
Your windowsill pelargonium will thrive throughout the winter and will even bloom, but not as heavily as it did outdoors, because winter lighting is usually less intense.
When Summer Comes
Regardless of the method used to maintain your pelargonium over the winter, you’ll still have to acclimatize it to outdoor conditions before planting it out for the summer. Once there is no risk of frost, place the plant outdoors in shade for first three or four days, then in partial shade for another three or four days, before placing it in full sun, its preferred condition, although partial shade will do. With this kind care, your pelargonium should bloom abundantly right through the summer.
That said, windowsill pelargoniums will still generally be much more attractive and floriferous in the summer than those spent the winter in forced dormancy: it isn’t easy for a plant used to growing all year to fully recover from forced dormancy!