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What is a Geranium?

What is a Geranium? | Copyright GreenPlantSwap Ltd

Oh, we all know what Geraniums are – those smelly things that old ladies grow on window ledges, or which old boys grow in greenhouses, and take to the village plant competition.

But there's so much more to them than that...

Geranium or Pelargonium?
Let's start with the big question: what's the difference? For that matter, is there a difference? Does it matter?

In reverse order, yes, it always matters: you won't get the best from any plant unless you know what it is; yes, there is a difference: these two plant groups are related, but they are quite distinctly different, and you can look for these differences yourselves, in several different ways. And here is how!

Botanically, seed dispersal is different: both Geranium and Pelargonium produce fruit that are long, slender and pointed, hence their common name of Cranesbill or Stork’s-bill: these seed pods are shaped rather like a long, pointy beak. With Geranium, when the seeds are ripe, the seed capsule explodes, pinging the seeds far and wide. Pelargonium, on the other hand, have evolved to spread themselves by wind, so as the seed head splits, silky-haired seeds are released to waft away on the winds, rather like Dandelion or Willowherb.

Also botanically, most Geraniums have ten fertile stamens whereas in Pelargonium, only seven of the ten stamen are fertile: but as this is somewhat hard to spot, don't worry about it - there are much easier methods to tell them apart!

Horticulturally, Pelargoniums are not hardy: they are often grown or labelled as “annuals” because they are the ones that have to be brought indoors and cosseted on windowsills or in greenhouses through the colder months of the year, whereas most (but not all) of our Geraniums are hardy perennials, which will happily survive the frost, asking only for a haircut early in the spring to remove tatty foliage before leaping into flower again.

But how can you tell the difference in the middle of summer, when they are flowering, have not set seed yet? Well, there are several things you can look for and, as always with botany, it's always best to look at all the features before making a decision.

Firstly, look at the general growth of the plant: Pelargoniums have thick, fleshy stems which they use to store water against times of drought in their native South Africa, and these stems become woody and firm, allowing the plant to grow strongly upright, sometimes several feet high. In the UK this means they will often require staking, as any irregularity in watering can result in those succulent stems bending and deforming. Geraniums are much lower-growing, usually only forming low mounds of foliage, with the flowers held on thin wiry stems.

Secondly, look at the flowers: Geranium have five identical petals, so they are what is known as “radially symmetrical”, which means that no matter how you twiddle the flower stem, the flower looks the same – it has no “left” and “right”, or “up” and “down”. In Pelargonium on the other hand, the two upper petals are different from the three lower ones, making the flower symmetrical, but only from one viewpoint: as soon as you twiddle the stem, the flower is no longer symmetrical. This is called bilateral symmetry: “bi” meaning two and “lateral” meaning “to the side”, indicating that the flower has two sides, a left and a right, like a face.

In botanical terms, (brace yourself for some botany!) these two flower types have their own names: actinomorphic is the one with radial symmetry, the Geranium, and zygomorphic is symmetrical only in one plane, ie the Pelargonium. It is easy to remember the difference if you think of zygomorphic beginning with z, like a zoo: and zoos have animals, with faces. However, having said that, Pelargonium have been so highly bred now, that sometimes the flowers are so complex, ruffled, coloured and tinted that it can be hard to tell if they are radially symmetrical or not.

Thirdly, and most usefully (as plants do not flower every day, but usually have leaves to look at), the leaves of Geranium are usually deeply divided, which means they look as though someone has been at them with the scissors, whereas those of most groups of Pelargoniums are “entire”, which means that the edges are not cut – although they are often lobed, or wavy.

Fourthly, although this is only a generalisation, the true bright reds are only found amongst the Pelargonium: Geranium flowers tend to have shades of white, into pink through to cerise, but they lack the really bright, showy scarlets.

The botanical name, Geranium, is derived from the Greek word γέρανος (géranos) which means crane, and when they say crane they mean the long-billed bird, not the construction site machinery, so this is clearly a reference to the elongated seed pod.

How to grow Geraniums
Buy them, plant them, water them in, let them get on with it! Is it really that simple? Well, yes! Hardy Geraniums are one of the best flowering ground cover plants, and if they start to look sad and tatty after flowering, just shear off the top growth, quite cruelly, water them well and within a couple of weeks they will have produced fresh new mounds of foliage, and – depending on the time of year – a new flush of flowers. Don't give them any feed though: fertiliser will prompt them to make too much new growth, so the new stems will be long, lank and floppy.

When the second flush of flowers have finished, it is usually a good idea to cut them back again, otherwise they will set seed all around the garden. It also helps to keep the individual plants from sprawling too far, and many people regularly propagate and replace their plants, to keep them looking fresh. Propagation is very easy: you can take semi-ripe cuttings in summer, you can collect the seed, or you can divide the original plant, which is best done either in autumn as the plants are starting to go dormant, or in spring as they are just thinking about putting on a growth spurt.

What are Geranium used for?
Their best and most common use is as long-season flowering ground cover: most of the hardy Geraniums will spread themselves out in a luxurious manner, smothering weeds (and other plants if you are unlucky) and providing colour for many months, particularly if you dead-head or shear them back after the first flush are produced.

As they will tolerate quite poor, dry soil, they are ideal for stabilising banks and bringing some interest to shady woodland-type beds.

And, of course, they are ideal for decorative pots.

The Geranium in popular culture
Unlike many plants, Geranium never quite made it to become a popular girls' name: but in the Language of Flowers there are many entries for Geranium, starting with “Gentility, Esteem” for Geranium in general, moving through “Unexpected meeting” for Geranium, lemon scented; on the other hand, you would have an “Expected meeting” if you were presented with a Geranium, nutmeg scented.

An apple-scented Geranium would indicate “Present preference”, although it is not clear if you are preferring the present Geranium, or the present company: and for the basic Crane's Bill Geranium, the meaning is simply “Envy”.

Meanwhile, over in North American (it's amazing what you can find on the internet), in their version of the Language of Flowers, Geranium stands simply for "Stupidity: Folly" which is not very nice!

Which Geranium where?
Geranium pratense is our native Crane's Bill, forming a neat mound of finely cut foliage, and happily producing two flushes of flowers through the summer: our Plant Finder has five cultivars ranging from white through to deep purple, all of which will benefit from being cut back hard when they start to look tatty, and all of which will make good ground cover in beds or borders, whether in full sun or in part shade.

Geranium come in a variety of sizes, from the smaller alpine-style Geranium cinereum, through the ankle-height Geranium macrorrhizum with its aromatic leaves and fresh, bright green foliage, through to the knee-high Geranium phaeum – ‘Mourning Widow’ - which can be a bit rampant, but which has interesting and unusual dark purple flowers, held on stiff upright stems.

For woodland planting, you can't beat Geranium maculatum, the spotted geranium, which is also known as wood geranium, or wild geranium: and for shady beds, Geranium psilostemon and Geranium sylvaticum will also do very well.

As far as colour is concerned, most Geranium are available in shades of white through pink to deep purple, but Geranium ‘Rozanne’ is one of the few with genuinely blue flowers, although Geranium himayalense (Lilac geranium) will give it run for its money, as will Geranium ibericum (Iberian cranesbill).

One Geranium with a particularly gruesome name is Geranium sanguineum or Blood-red geranium, but it is actually a species with several lovely cultivars - we have five in our Plant Finder already - in shades of strong cerise: and there is even a white version, Geranium sanguineum ‘Album’ which makes the name seems rather ridiculous.

And finally, the one we all try to avoid is Geranium robertianum or Herb Robert, whose red-tinged octopus-like rosettes are well known and much hated by gardeners - but they are an easy weed to pull out, and they do make excellent ground cover, and there is even a cultivated, white-flowered variety, predictably named Geranium robertianum ‘Album’ – ‘White Herb Robert’

A Geranium by any other name...
So, other than Pelargonium, are there any other plants which are called Geranium, but which are not actually either Geranium or Pelargonium? Well, Rosa moyesii ‘Geranium’ is a rose which looks, to be honest, simply like a rose, and whose chief claim to interest is not so much the flowers, which are a fairly ordinary rugosa-type open single bloom, but the hips, which are a bright scarlet, and which have a very unusual flask-shape.

Then there are two alleged Strawberry geraniums: Saxifraga sarmentosa and Saxifraga stolonifera: both of these have lobed, rounded leaves which could, in poor light, be considered to at least look a little bit like a Geranium...

...unlike Tanacetum balsamita, with its white daisy-flowers, which is completely mis-named as Mint geranium: but no more so than Lantana montevidensis (Weeping lantana, or Pole-cat geranium), which looks like a lacecap Hydrangea, or Ixora coccinea - whose many names include Flame of the woods, Jungle flame, and Jungle geranium - which looks nothing like a Geranium, as it has starry-petalled flowers, in shades of bright scarlet!

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