Balcony geranium (Pelargonium): overwintering, cuttings and flowering
The red window boxes on Belgian façades, the hanging baskets spilling over balconies, the pots on the windowsill: everyone calls them "geraniums". Yet almost none of them are. They are pelargoniums, plants from southern Africa whose balcony varieties cannot stand frost. And now, before the first frosts, is the time to decide their fate.
Geranium or pelargonium: where does the confusion come from?
In 1753, Linnaeus placed all these plants in a single genus, Geranium. The zonal geranium was then called Geranium zonale. In 1789, the French botanist Charles Louis L'Héritier de Brutelle moved the southern African species into a separate genus, Pelargonium. Botanists followed; everyday language never did.
Both genera belong to the same family, the Geraniaceae, and their names tell the same story: their elongated fruits look like a bird's beak. Geranium comes from the Greek geranos, crane; Pelargonium from pelargos, stork.
To tell them apart in the garden, look at the flower:
| Pelargonium (balcony "geranium") | True geranium (hardy geranium) | |
|---|---|---|
| Flower | Irregular: the two upper petals differ from the three lower ones | Regular: five identical petals arranged in a star |
| Origin | Mainly southern Africa | Temperate regions worldwide, including Belgium |
| Winter in Belgium | Freezes: bring in or take cuttings | Hardy: stays in the garden |
| Use | Pots, window boxes, hanging baskets | Borders, ground cover, hedge bottoms |
The pelargonium also has, at the back of the flower, a small nectar tube (the hypanthium), absent in the true geranium. The genus has nearly 300 species according to the Kew Gardens reference, and the great majority come from southern Africa, with a remarkable concentration in the south-west of South Africa, around Cape Town.
True geraniums have their own article: Hardy geraniums.
The main groups of pelargoniums
- Zonal: the window-box classic, upright habit, round leaves often marked with a dark horseshoe band (hence the name). It descends largely from Pelargonium zonale.
- Ivy-leaved: trailing stems and glossy leaves reminiscent of ivy, ideal in hanging baskets and balcony boxes.
- Regal: large ruffled, blotched flowers, earlier but shorter flowering; prefers light partial shade.
- Angel: close to the regal but more compact and bushy.
- Scented-leaved: modest flowers, but leaves strongly scented when touched (rose, lemon, mint…). The "rose geranium" belongs here.
Keeping it flowering all summer
- Planting: outdoors only after the last frosts, in practice around mid-May in Belgium, after a few days of hardening off.
- Position: full sun for most; zonals tolerate a little shade, regals prefer partial shade.
- Compost: free-draining. Pelargoniums fear excess water far more than drought.
- Watering: moderate, letting the surface dry between waterings. A saucer permanently full of water rots the roots.
- Feeding: a balanced fertiliser every two weeks in spring, then a potassium-rich feed (tomato-type) every two weeks during flowering.
- Deadheading: remove faded flowers regularly, with their stalk, to keep the blooms coming.
Overwintering: three methods
In autumn, bring the plants in before the first frost. Three ways to do it, from the safest to the riskiest:
1. Keep the plants in pots, under cover
This is the most reliable method. Place the pots somewhere light, airy and frost-free: conservatory, cold greenhouse, a cool room in front of a window. At around 7 to 10 °C, some varieties even keep flowering gently. If space is short, cut the stems back to about ten centimetres.
In winter, water very little: just enough to stop the rootball drying out completely. Remove yellowing or mouldy leaves. At the end of winter, resume watering, pinch the stems to make the plant branch, and repot in spring.
2. Take cuttings and keep only the young plants
Cuttings taken in late summer or early autumn take up much less space than old plants, and give more vigorous plants the following year (see below). They spend the winter on a bright windowsill, with little water.
3. Store the plants bare-rooted
Our grandparents' method, and the least reliable: lift the plants before the frost, shake off the soil, let them dry, then wrap them in newspaper or hang them upside down in a cool, frost-free place. In spring, soak the roots, pot up and cut the stems back to about ten centimetres. Some plants will not grow again: keep this method for varieties you are less attached to.
Fuchsias and dahlias also need to be brought under cover now: see our fuchsia and dahlia guides, as well as our article on overwintering garden plants (in French).
Taking pelargonium cuttings
This is one of the easiest cuttings in the garden, and the best way to keep a favourite variety.
- When: from late summer to early autumn, while the plant is still growing. Spring works too.
- Take a young, non-flowering shoot tip three to six nodes long, cutting cleanly just below a node (where a leaf joins the stem).
- Prepare: remove the leaves from the lower half and any flower buds. Let the cut dry for a few hours to limit rot.
- Plant in a light, free-draining mix (compost with sand or perlite), barely moist. Rooting hormone is optional.
- Place somewhere warm and bright, out of direct sun. A cloche or bag keeps the humidity in, but pelargonium's fleshy stems rot easily when enclosed: if you cover them, air them every day.
- Wait: roots usually appear within three to four weeks. Then pot each cutting into a small pot.
Pests and diseases
- Rust: brown pustules under the leaves. Remove affected leaves and give the plants air.
- Grey mould (botrytis): grey mould on flowers and leaves, especially in winter in a damp, poorly ventilated room.
- Whitefly: small white insects that fly up when the plant is touched, common indoors.
- Aphids and thrips: they weaken the plant and can transmit viruses.
- Vine weevil: its larvae eat the roots in pots; a plant that wilts for no obvious reason deserves a check of its rootball.
The "mosquito-repellent" geranium: a myth
A lemon-scented pelargonium is often sold as a mosquito repellent. A field study published in 1996 in the Journal of the American Mosquito Control Association tested it: it offered no protection, and mosquitoes even regularly landed on the plant. It smells nice when you crush its leaves; it does not protect you from a bite.
Test yourself
Sources
- Fibrex Nurseries. (n.d.). A step-by-step guide to taking pelargonium cuttings. Fibrex. https://fibrex.co.uk/blogs/news/a-step-by-step-guide-to-taking-pelargonium-cuttings
- Hughes, K. (2009). Cultivation of the genus Pelargonium under glass. Sibbaldia: The Journal of Botanic Garden Horticulture, (7). https://journals.rbge.org.uk/rbgesib/article/download/163/151
- International Plant Names Index. (n.d.). Pelargonium zonale (L.) L'Hér. IPNI. https://www.ipni.org/n/377229-1
- Lawrence, E. (2002). Pelargonium graveolens. PlantZAfrica, SANBI. https://pza.sanbi.org/node/10722
- Matsuda, B. M., Surgeoner, G. A., Heal, J. D., Tucker, A. O., & Maciarello, M. J. (1996). Essential oil analysis and field evaluation of the citrosa plant Pelargonium citrosum as a repellent against populations of Aedes mosquitoes. Journal of the American Mosquito Control Association, 12(1), 69–74.
- Plants of the World Online. (n.d.). Pelargonium L'Hér. ex Aiton. Royal Botanic Gardens, Kew. https://powo.science.kew.org/taxon/30302759-2
- Royal Horticultural Society. (n.d.). How to grow pelargoniums. RHS. https://www.rhs.org.uk/plants/pelargonium/growing-guide