Pelargoniums are among the most popular summer flowers, the leaves of the South African pink, red and white beauties bringing vivid colour and often wonderful scents to the garden. But pelargoniums can offer much more than that, as I discovered on a visit to the Swiss capital, Bern, earlier this month.

The Bernese proudly call the pelargonium Queen of the Balconies and an annual competition is held to find the city’s most attractively pelargonium-crammed balcony. The lucky, or should I say skilled, winner is duly crowned king or queen.

This mania recently took a step further this year with a project called Geranium City, explaining the secret of success with pelargoniums, describing how to grow and maintain the plants, focusing on the importance of sparse watering. Interestingly, the general advice is not to put plants outside until the temperature is safely above 10C.

Four organisations collaborated to mount an impressively varied festival, with talks, exhibitions and displays taking place throughout the summer.

In April, citizens were invited to have one or two pelargoniums for their own balconies and gardening body Stadtgrün Bern offered to look after any of these tender plants over the next winter. There is also a display of 100 planters of a range of pelargoniums throughout the city, in addition to the customary window boxes.

The city university’s botanic garden is playing an important educational role in this festival, and is the location of a highly informative exhibition organised by Dr Stefan Boch. “We want to show people how diverse pelargoniums can be," he told me. "The botanic garden has 22 pelargonium species and Friburg University have loaned us another 33 species.”

Boch told me the Swiss are just as bad as many Scots at calling pelargoniums geraniums. Pelargoniums, comprising around 280 species, are one of seven genera, or groups of species, in the botanical family Geraniaceae. But, perhaps confusingly, geraniums – with 430 species – are a completely different genus within the family. Apples and plums are members of the rosaceae family, but we don’t call them roses.

Nothing was more marked in the Botanics’ exhibition than the sheer diversity of pelargoniums. I could scarcely recognise some of the plants as pelargoniums. P bowkeri has such deeply divided leaves that it could almost be mistaken for dill.

And there could be so much foliar interest in a planting comprising species pelargoniums. P radens provides stiff, narrow, branched leaves, while P graveolens has deeply incised ones. You touch its irresistible velvety leaves and release a cloud of rose scent. And then there’s P caffrum, with its five shiny, narrow leaves.

Or P denticulatum with reduced leaves that look like tamarisk, edged with sharply pointed teeth: I was captivated by the many unusual leaf shapes. But the tiny star-shaped flowers also caught my eye. Pelargoniums come in many more shades and colours than the familiar whites, pinks and reds. Take the creams, peaches and even yellows and you’ll see what I mean. Yes, I was privileged to see a very rare, yellow-flowered pelargonium which hasn’t yet been identified. The flowers of these species pelargoniums are always much smaller than the modern hybrid cultivars, but their charm and elegance more than compensates.

Although modern doubles don’t have pollen and therefore can’t attract bees and other insects, all the species and single-flowered ones do. And some of the exhibits made themselves doubly attractive with brightly coloured pollen.

Several of these species are part of the scented pelargonium group and bombard the senses with rose, peppermint, ginger, pineapple and other delights. But I was astonished to find the leaves of P acetosum even made the perfect nibble, tasting very like sorrel.

Visit woottensplants.com for a broad selection of species pelargoniums.