Hardy geraniums: the true geraniums, tough and easy
They have nothing to do with the red window boxes on balconies. True geraniums, of the genus Geranium, are hardy perennials that spend the winter outdoors without any protection, come back every spring and cover the ground with blue, pink, mauve or white flowers for weeks. They are among the easiest and most generous plants in a Belgian garden.
True geraniums in brief
The genus Geranium has 337 species according to the Kew Gardens reference, spread across the world's temperate regions and the mountains of warmer ones. Several grow wild in Belgium, such as herb Robert, common at the foot of hedges and old walls.
You recognise them by their regular flower: five identical petals arranged in a star, whereas the pelargonium flower has two upper petals that differ from the three lower ones. Their elongated, beak-shaped fruit earns them the nickname cranesbill, which is also the meaning of their name, from the Greek geranos, crane.
Everything about the balcony geranium is in our article Balcony geranium (Pelargonium).
Choosing for the spot
This is the real key to success: there is a hardy geranium for almost every corner of the garden.
| Situation | Examples | What they bring |
|---|---|---|
| Full sun, border | Geranium Rozanne, G. sanguineum, G. 'Orion' | Long flowering, from early summer to autumn for Rozanne |
| Sun, well-drained soil, rock garden | G. renardii, G. (Cinereum Group) 'Ballerina' | Low plants, decorative foliage |
| Partial shade | G. × oxonianum 'Wageningen', G. 'Dilys', G. endressii | Tolerate the light shade of a tree or hedge |
| Shade, even dry | G. macrorrhizum, G. phaeum | Dense ground cover; aromatic leaves in macrorrhizum |
| Meadow, natural garden | G. pratense and its varieties | Large clumps of blue flowers, a country feel |
The most famous is probably Rozanne: violet-blue flowers with a white centre from July to October, on a clump around sixty centimetres high that spreads widely. At the Chelsea Flower Show in 2013, it was named "Plant of the Centenary".
Not all are hardy: two species from the Atlantic islands, G. maderense and G. palmatum, are frost-tender. They are the exceptions.
Planting
- When: preferably in spring, especially in heavy soil, where a young plant put in during autumn may rot over winter.
- Soil: almost any garden soil will do, on one condition: it must not stay waterlogged in winter.
- Spacing: leave room for ground-covering varieties such as Rozanne, which spread over more than half a metre.
- Watering: water well at planting, then in dry weather give a thorough soak from time to time rather than a little every day. Once established, most look after themselves.
There is no need to add fertiliser to ordinary garden soil: hardy geraniums flower very well without it.
Cutting back for a second flush
This is the move that makes all the difference. Many hardy geraniums flower in June, then flop and look tired. As soon as the first flowering is over, often in June or July, cut the whole clump back to ground level. Within a few weeks, fresh, dense foliage grows back, and some varieties flower again.
Continuous-flowering varieties such as Rozanne do not need it: just cut back the stems that sprawl too far.
In autumn, simply remove damaged leaves. Some species, such as G. macrorrhizum, keep part of their foliage through winter: leave it.
Dividing and propagating
Clump-forming hardy geraniums become bare in the centre over time. After a few years, in spring, dig up the clump, cut it into several pieces with roots and buds, and replant the most vigorous. It is also the simplest way to get more plants, and to give some away.
Species sometimes self-seed, and their seed can be sown in spring. Garden varieties, on the other hand, come true from division or cuttings, not from seed.
Possible problems
They are rare. Powdery mildew (white felting on the leaves) appears mainly in dry weather: cutting the clump back often solves the problem. In pots, vine weevil larvae can devour the roots. In the ground, most hardy geraniums need no treatment or special attention.
Test yourself
Sources
- Plants of the World Online. (n.d.). Geranium Tourn. ex L. Royal Botanic Gardens, Kew. https://powo.science.kew.org/taxon/urn:lsid:ipni.org:names:327764-2
- Rice, G. (n.d.). 10 award-winning hardy geraniums for the garden. Royal Horticultural Society. https://www.rhs.org.uk/plants/trials-awards/using-award-winning-plants/10-award-winning-hardy-geraniums-for-the-garden
- Royal Horticultural Society. (n.d.-a). How to grow geraniums. RHS. https://www.rhs.org.uk/plants/geranium/growing-guide
- Royal Horticultural Society. (n.d.-b). Iconic plants of Chelsea. RHS. https://stories.rhs.org.uk/iconic-plants-of-chelsea/index.html