24: Autumn 2009

Author: Sheila Phillips

Chocolate Cosmos

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Chocolate CosmosSheila Phillips

The Chocolate Cosmos, Cosmos atrosanguineus, formerly Bidens atrosanguinea, is one of my favourite flowers. In the Compositae family, it is sometimes also called the Black Cosmos. It is a compact plant with flowers and pinnate leaves somewhat like those of a small single dahlia although the 1″ velvety flowers, held aloft on elegant branching stems, are the colour of chocolate and their unique heavenly scent is also of chocolate. Bend the knees, nose to the flower – a good exercise for a handsome reward! Some sources say that the colour is deep maroon, darkening to brown later in the day with the scent of vanilla as well as chocolate but my own sense of smell is not that discerning. Cosmos is from the Greek word “kosmos” meaning harmony, “sanguineus” is blood coloured, and “atro” means dark.

Also like the dahlia it forms a tuber, though not until it is more mature; however, I cannot verify this as I have never dug mine up! It is a native of Mexico where it is now an endangered species, although the Mexican government is finally trying to reverse this. It was introduced to Britain in 1835. It is said in nearly all the literature to be a half-hardy plant which needs to be cut down to 2″, dug up, dried and stored each winter or, at the very least, protected by a cloche. Encouraged by one of our members in Perth who told me that hers had been in her garden continuously for about 10 years, I have left mine in my front garden here in Dundee for the past 4 years. Admittedly I mulched it with dried grass stems for the second and third winters, having been frightened into thinking that I had lost it after the first winter when it took so long to come to life again. Deep planting is also said by Jack Elliott to protect it. As I write (early January 2007, weather mild) there is still so much live foliage on it that I am reluctant to mulch it yet. I was interested to see in a recent ‘Gardening Which’ magazine that trials have shown that many plants hitherto thought to need lifting in the winter can actually be left in the ground, although this plant was not one of those being tested.

My plant has expanded gradually and has this past year had dozens of flowers on it for many weeks. The literature says it flowers from July until September but mine starts and finishes later than this. The waiting takes patience but is well worth it! It is said to grow to 3 ft. high but I have never seen it nearly this tall, although the stated spread of 18″ would apply to my own plant this year. There is now a cultivar called C. ‘Choca Mocha’ which is said to be more compact.

As with all Cosmos (the ‘Mexican Aster’), this species loves full sun, is moderately drought-tolerant once established, and needs to be in a well-drained position. It is also said to like alkaline soil. Propagation is by division, and cuttings can also be taken although I have not tried this, having been unable to find any suitable cutting material. As far as I can ascertain it rarely, if ever, sets seed in this country, although a lady in the Lower South Island of New Zealand is able to grow 100 new plants every year from seed set by her four plants. There is a slight variation in their flower colour but she says they are definitely true to species. Seed should be sown March to May, and division done in March or April. Tubers should be planted 15 cm deep. The flowers attract butterflies. But be warned – the tubers are a delicacy for squirrels!

First published in the Scottish & Northern Borders Group Newsletter, Spring 2008
and subsequently in Cornucopia Issue 24
© Copyright for this article: Sheila Phillips

This article was taken from a copy of Cornucopia that was published in 2009. You could be reading these articles as they are published to a national audience, by subscribing to Cornucopia.

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