Plant of the Month: August

Purity 2When everything else is looking a bit tired and dusty, there are some plants which you can rely on to go on and on. They are mostly ‘daisies’, Asteraceae, and mostly introductions from hotter climates, and my favourite is Cosmos. There are apparently 36 separate species, of which the best known in Europe are Cosmos bipinnatus and C. atrosanguineus (the so-called ‘chocolate cosmos’).

The greatest number of Cosmos species is found in Mexico, from where they have spread as far north as Washington State and as far south as Paraguay. They are found in India, especially in Kerala, in Japan and Korea, and in South Africa, where, allegedly, the plants were accidentally introduced as seed in fodder sent from South America to feed British horses during the Boer War.

Mixed Cosmos in a prairie planting.

Mixed Cosmos in a prairie planting.

Essentially prairie plants, they grow and spread so vigorously that some are regarded as pests: the yellow C. sulphureus, which can grow up to seven feet high, is defined as ‘invasive’ by the United States Southeast Exotic Pest Plant Council, though apparently it is planted en masse along the sides of motorways in Korea and Japan.

Cosmos sulphureus can be quite orange ...

Cosmos sulphureus can be quite orange …

... or a much more sulphurous yellow.

… or a much more sulphurous yellow.

Cosmos atrosanguineus was named by William Jackson Hooker (1785–1865) – intrepid voyager to Iceland, first director of the Royal Botanical Garden at Kew, initiator of the Icones Plantarum series and protégé of Sir Joseph Banks – in Curtis’s Botanical Magazine in 1861.

Plate showing chocolate cosmos, from Curtis's Botanical Magazine, January 1861.

Plate showing chocolate cosmos, from Curtis’s Botanical Magazine, January 1861.

He called it Cosmos diversifolius var. atro-sanguineus, noting that: ‘The question is if it can be safely referred to any described species.’ Earlier descriptions and illustrations are inadequate to determine this, but ‘We prefer adopting [an existing name] rather than encumber the system with new but doubtful species.’ He also says that: ‘Seeds of the plant were received by Mr Thompson, of Ipswich’ – the ‘baker botanist’ who produced his first catalogue in 1855 and developed what is now the Thompson and Morgan seed and plant company.

Scarily, C. atrosanguineus, introduced into British gardens in 1902, is extinct in the wild. All plants now stem from a single clone, and the seeds are infertile. Interestingly, the ‘chocolate’ smell from which it gets its popular name is in fact not chocolate but vanilla (the plant gives off vanillin), which of course is so often used to flavour chocolate that the two can be confused.

Cosmos atrosanguineus.

Cosmos atrosanguineus.

Cosmos bipinnatus (which has had 21 synonyms over the years) was named in 1791 by the Spanish botanist Antonio José Cavanilles (1745–1804), a correspondent of A.L. Jussieu and J.E. Smith, who also named the dahlia and cultivated many South American plants in the Botanical Gardens in Madrid, of which he was director. The Greek word κόσμος means ‘order’ (including the order displayed by the universe) as opposed to ‘chaos’, and hence also ‘beauty’. He gives a description, in his Icones et descriptiones plantarum quae aut sponte in Hispania crescunt aut in hortibus hospitantur, of the general characteristics of Cosmos (noting that the genus appears to differ from Coreopsis and Rudbeckia, other American members of the Asteraceae) and then of C. bipinnatus, with a plate delineating beautifully the complexity of the foliage.

Cosmos bipinnatus, from Cavanilles' Icones plantarum.

Cosmos bipinnatus, from Cavanilles’ Icones et descriptiones plantarum.

There are now hundreds of varieties of C. bipinnatus available to purchase, whether as seeds or plants, and the colour palette has growm from the original white and pastel pink to darker shades and even to yellow (‘Xanthos’): and there’s probably someone out there trying to fly in the face of nature by creating a blue one. It’s also possible to buy smaller varieties (since the wild plants and earlier hybrids can grow to several feet) which need less staking.

Cosmos 'Xanthos'.

Cosmos ‘Xanthos’.

My favourite is ‘Purity’, the purest white you can imagine (even purer than Tulipa purissima, which is saying something).

Cosmos 'Purity'.

Cosmos ‘Purity’.

Tulipa purissima

Tulipa purissima.

I also grow ‘Antiquity’, the flowers of which, according to Thompson and Morgan, are ‘rich burgundy on opening and change to an antique bronze-salmon when ageing’ – well, sort of, I suppose.

'Antiquity' in its prime ...

‘Antiquity’ in its prime …

... and as it fades.

… and as it fades.

Apart from ‘Antiquity’, I prefer the paler pastel colours: some of the darker pinks, in my opinion, have a rather blue tinge in the pink (cyan in the magenta, as it were), not dissimilar from pink perpetual peas, which turn a sort of pale inky blue as the flowers wither.

Too bluish a pink?

Too bluish a pink?

I’ve recently discovered that you can take cuttings, and will certainly try this. I lost a massive number of seedlings last year to slugs, and though this year I took better precautions, successful cuttings will get the plants off to an earlier start and avoid the germination problems which these usually very easy plants sometimes encounter (there’s a very interesting article about seed quality here).

A paler shade of pink.

A paler shade of pink.

Cosmos are a very virtuous plant (quite apart from their beauty) because bees, hoverflies and butterflies love them.

This bee obligingly posed at CUBG.

This bee obligingly posed at CUBG.

Like many of the Asteraceae, they provide bright colours as a guide, a flat landing-place and readily accessible nectar (except of course in the case of the over-bred fluffy doubles recently appearing on the market). For more insect-friendly flowers see the London Beekeepers’ Association website.

Cosmos 'Double Click White'.

Cosmos ‘Double Click White’: not good for bees …

There are dozens of buds still appearing, so if I keep dead-heading I should have flowers for at least another month; and, if the cuttings work, plants for another year. Not bad, out of a couple of packets of seed …

Caroline

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One Response to Plant of the Month: August

  1. Pingback: Plant of the Month: August 2017 | Professor Hedgehog's Journal

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