Graham Rice discusses the genus that has been named after the Greek for 'beautiful'.
There was a time when country house gardens grew rows of cosmos in separate colours for cutting. Then there was a decline and for some years about the only type grown was the 'Sensation' mixture. Now new forms and attractive single colours are again appearing in catalogues, inspired by renewed interest from commercial cut flower growers.
There are two main types of cosmos that are grown from seed, those derived from C. hipinnatus and those developed from C. sulphurous. And here the confusion starts straight away for it seems that the yellow forms of C. hipinnatus have been known in the past as C. sulphurous, a name now applied to the shorter, broader leaved types.
But rather than wade into deep taxonomic water I'll simply stick with the names the catalogues now use.
Just to be perverse, I'll start with the perennial Cosmos atrosanguineus which cannot be raised from seed. I say cannot be raised from seed, thirty years ago seed was available and there are occasionally reports that plants have set seed but I've never seen seed or seen it listed. The demand for this very popular plant is now satisfied by plants multiplied by micropropagation.
The flowers, in colour and scent much like plain (rather than milk) chocolate, set this plant apart. It reaches about 2ft (60cm) with dark stems and narrow leaves and has small tuberous roots. It looks stunning in a mass, but you'll have to take cuttings from young shoots to build up stock.
In the 1950s, Cosmos diversifolius was listed in catalogues but I've never seen or grown it. To put it simply, it's a lilac or rose pink version of C. atrosanguineus. I wonder if it's still in cultivation. If it is, some seed would be much appreciated.
The familiar annual Cosmos hipinnatus is a tall plant, sometimes reaching 5ft (1.5m) in height but generally a little shorter, depending on the variety. The foliage is bipinnate, that is to say it is first divided into opposite segments and then these too are divided in the same way. As the individual segments are themselves very long and narrow the resulting effect is very lacy and delicate.
The freshly coloured, lacy foliage of established plants not only sets off the flowers well but makes a good background for other annuals. The flowers are carried on single stems or sometimes in open heads. In most varieties the stems are long enough for cutting.
The flowers come in three forms. Most varieties have single flowers with eight sterile petals or ray florets and a broad yellow disk of fertile florets. Some have a few shorter petals around the disk and one has tubular petals. There are yet no fully double varieties as there are of annual chrysanthemums for example. There is now a Double-Semi Double strain called Cosmos ‘Double Click’ in a wide range of colours and look spectacular in borders.
The Japanese in particular are putting a lot of work into breeding new cosmos for cut flowers and in the future years we can look forward to some really good new varieties.
'Butterkist', 'Lemon Cream', and 'Yellow Garden' are alternative names for a recently introduced variety from Japan that is different from most in two ways. First of all the 2-3in (5-7.5cm) flowers are yellow with a pale ring around the disk. Secondly, like many of the older varieties they are very late flowering. Sown in spring they will not flower until September when the plants have become very tall. Sown in June or July their flowering time is unchanged as it's controlled by day length but the plants are shorter and more manageable.
'Candy Stripe' is a very distinctive variety reaching about 3ft (90cm) with the white petals edged in crimson. This is a very striking variety with the amount of crimson intentionally varying from a very attractive fine picotee edging to more lurid combinations featuring rather too much crimson. There are some with no white at all. This is difficult to place in the garden and selection for the picotee edged type would be worthwhile - but special forms of cosmos are notoriously difficult to keep stable.
'Gloria' has especially large flowers, up to about 4in (10cm), in pale pink with a dark central stripe in each petal. The stems are a little longer than usual making this a good variety for cutting.
An almost double variety is 'Psyche' which has a frilly ring of half-length petals around the eye. It comes in a mixture of various pinks and white and although it's rather variable it makes an interesting cut flower.
'Purity' is a stunning pure white and one of the best. Reaching 4ft (1.2m) in height the 3in (7.5cm) flowers are slightly ruffled and slightly toothed at the tips. The foliage is pale green and sets off the flowers well.
In its earlier days 'Sea Shells' was a very variable variety. It's unique in that the eight petals of each flower are tubular instead of flat so that the colour on the back of the petals (on the outside of the tube) is more prominent than that on the 'front' (inside the tube). The effect is probably less showy than varieties like 'Sensation' but a great deal more stylish.
In early selections half the flowers would be in the usual flat petalled form and the effect would be destroyed. Now the variety has been improved so they are 100% 'sea shells' and in various pinks and white. The plants are about 3ft (90cm) in height.
'Sensation', sometimes known as 'Early Sensation', is the one you find in most catalogues. Strains differ so you can't be sure exactly what you're going to get until you grow it; some strains have no white, deep red is usually missing but you can be sure of a range of pink shades. Plants are tall and bushy, sometimes over 4ft (1.2m), and need plenty of space.
One of the 1991 Fleuroselect Gold Medal winners is 'Sonata', a stunning dwarf white reaching only about 18in (45cm). The pure white flowers are prettily fluted, held well above the foliage and up to 4in (10cm) across making a very impressive plant. This is the first of a new generation of dwarf types, other colours and mixtures are on the way. Older dwarf types do not seem to be available at present.
"Trianon' is a bright crimson 'Sensation' type with large single flowers on tall bushy plants and is the darkest available in separate colours.
'Versailles Improved' is another 'Sensation' type with rosy lilac flowers, each with a deep crimson ring around the yellow eye.
Finally the plants which are now known as Cosmos sulphurous. These have foliage rather similar to that of a French marigold, though perhaps a little smaller, and flowers which are at best about 2in (5cm) across.
The 'Bright Lights' mixture varies in height from 18-30in (45-90cm) making rather an uneven group. The flowers are in just three colours - deep orange, pale orange and a slightly orangey yellow. The flowers are on long stems but the effect is rather sparse and tatty unless they are dead headed regularly.
More even in height is 'Diablo' in flame red and reaching about 2-3ft (60-90cm) while the rather shorter new 'Ladybird' is a very piercing, iridescent orangey red.
'Sunny Gold' and 'Sunny Red' are also more even in height at about 18in (45cm) and distinctly upright in growth with flowers on shorter stems giving a more colourful effect. The gold is actually a gold tinted yellow while the red is just the orange side of a true red. The flowers are semi-double and need regular dead heading to look their best.
So that summarises the varieties available, fortunately none is difficult to raise or grow in the garden.
The bipinnatus types are raised either as hardy or half-hardy annuals. The seeds are long, curved and easy to space sow in a peat or loam based compost in April at 60F (15C). They germinate in a couple of weeks and are best pricked out in 3in (7.5cm) pots as they grow quickly. Once established in their pots keep them cool to prevent them getting too large too quickly. Harden off and plant after the last frosts in your area. The taller types can go 18in (45cm) apart, smaller varieties 12-15 in (30-38cm) apart.
These bipinnatus types can also be sown outside where they are to flower, although the seed of 'Sonata' may prove too expensive for this relatively wasteful approach. Sow very thinly in May about half an inch (l-2cm) deep, thin out first to 3in (7.5cm) and then progressively to their final spacing.
'Yellow Garden' is best sown later, June or even July, pricked out into pots and then planted in gaps left by early plants for late flowering. It can also be sown in September or October and over-wintered in pots indoors for spring flowering.
The sulphurous types can be treated in the same way as the bipinnatus varieties but are less successful when sown outside - raising them in the greenhouse is definitely preferable and with a germination temperature of 70F (21C).
Cosmos have many uses in the garden. Unlike comparable annuals such as annual chrysanthemums, cosmos will not burn up by the end of August in a hot British summer and so although the intensity of their display may be less, they will flower until well into the autumn.
The bipinnatus types are not fussy as to soil and any reasonable conditions in full sun suits them well. The taller types may need shelter from strong winds as they make bulky plants and can be blown over; alternatively they can be staked when approaching full size. Ensuring they don't get parched is a help and dead heading not only improves the appearance, especially of the whites, but helps promote further flowering.
Tall varieties such as the 'Sensation' and 'Sea Shells' mixtures and especially 'Purity' are fine plants for the back of the annual border, for spaces in a herbaceous border and for gaps in a new mixed border.
The fact that most carry their flowers towards the top of the plant is by no means a disadvantage as the fresh, finely divided foliage is a superb background for shorter varieties.
Associate them with large leaved plants such as Ricinus 'Impala' or those with harmonising foliage like Eucalyptus globulus or foliage in a strongly contrasting colour like the deep red Hibiscus 'Coppertone'. Plants with a contrasting stiff, upright habit like larkspur, especially in a colour not seen in cosmos such as 'Imperial Blue Bell', would also be a good choice.
'Sonata' is a perfect mixed border filler, its neat habit, fresh foliage and pure white flowers fitting happily into almost any good sized space although even this shorter variety has the capacity to elbow more delicate plants aside. I'm going to try it in a sea of Cynoglossum 'Firmament' or perhaps Echium 'Blue Bedder'.
The sulphurous types are a little more fussy and thrive in the hottest, sunniest spots you can find. In cold, windy beds and in wet soil they are less than successful.
But in the right spot they are good plants for fiery associations with Cannas, Crocosmias, Heleniums, mahogany and sulphur Marigolds and dark leaved Beetroot.
Finally, both types make useful cut flowers although the bipinnatus types are the most frequently used. The sulphureus varieties especially 'Diablo' and 'Bright Lights' mixture are useful for small posies but 'Sea Shells' and 'Yellow Garden' are the real stars.
Cut them as the buds are opening and put them in water at once; carrying them around the garden on a hot day before giving them a drink will shorten their vase life. The tubular petals of 'Sea Shells' are unique in their shape and bicolour effect, but note that the white fades prettily to palest pink which might not suit your arrangement. Even the shorter types have long enough stems for cutting but I would also suggest 'Purity' and 'Versailles Tetra'.
For more advice on filling your garden with stunning displays of annuals this summer, head to our annuals hub page - our one-stop-shop for everything to do with annual flowers & other bedding plants.
Graham Rice is a horticultural journalist and author with a particular interest in annual plants.
Source of article
Growing From Seed - Winter 1990-91 Vol. 5 Number 1
© The Seed Raising Journal from Thompson & Morgan