Cosmos is having a great summer. Growing conditions have been ideal and it has taken advantage to show just how good it can be. Indeed, it never fails to look well, and it is thoroughly reliable, but some years just suit it perfectly and, when that happens, it is a real delight.
But it is not a rarefied sight, because it is widely grown and can be seen waving its large pink or white flowers in many gardens these days. It is a plant that suits the current taste for flowers of a more natural appearance in contrast with the rigid ranks of bedding plants once commonly seen in gardens. It brings a lovely summery airiness to the garden, its fast growth enlivening its surroundings.
Strictly speaking, this is a bedding plant, a half-hardy annual, but it is not typical, like petunias, begonias and impatiens. Cosmos is tall and can reach one metre and more, easily. It has much divided leaves, very fine and almost hair-like. The plant branches freely from the early stages to make a loose bushy structure. Starting to flower as quite small plants, each of the branches produce a succession of flowers, branching further as the season moves on.
The flowers are large, shaped like a shallow saucer and about eight centimetres across. They are usually single-flowered, a simple and appealing flower shape. It looks very like a single-flowered dahlia, and it is closely related, both being members of the daisy family and native to Mexico. This provenance also explains its lack of hardiness against frost. Cosmos is growing, flowering and making seeds in the same year. The seeds are sown in March or April with a little bottom heat, or in a warmish place. The seedlings grow rapidly and get tall quickly and should be potted on as necessary, and planted out after hardening off at the end of May.
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The colours are mainly pink, purple-pink, or white, but the range has been pushed by the breeders into deeper tones and some red sorts. There are also double-flowered kinds, but these lack grace. There are curious quilled cultivars that can look a bit quirky.
There are yellow and orange varieties from a related species but these are much smaller, although they can be very pretty too, especially with grasses nearby. Strangely, the two-colour ranges are not a happy combination, even though they are closely related.
There is also the perennial chocolate cosmos with dark-red flowers richly scented of chocolate. Unlike the pink and yellow species, which are annuals and must be sown each year, the chocolate cosmos is perennial with a dahlia-like tuber. It needs good soil, not too rich, well-drained in full sunshine, and it needs to be mulched, or lifted, for winter protection.