Among the garden plants grown for their scent, chocolate cosmos (Cosmos atrosanguineus) certainly stands out from the crowd. Yes, as its common name suggests, its flowers really do smell like chocolate, especially at the end of a sunny day. The aroma comes from the vanillin that the flower produces… the same substance that gives cocoa its characteristic odor.
Besides, the little flowers are such a dark red (the name atrosanguineus means dark blood red) they can also be said to be chocolate colored… at least, if you use a bit of imagination. After all, they are certainly as chocolate-colored as red velvet cake and it is a type of chocolate cake. The flowers are at their darkest and most chocolaty color when they open, becoming dark wine red over time.
Chocolate cosmos has pinnate leaves and reaches 30 to 60 cm in height. It resembles the well-known sulfur cosmos (Cosmos sulphureus), a popular garden annual, whose flowers are about the same size (about 1 to 1 ¾ inches/2 to 3 to 4.5 cm in diameter) and of the same shape (6 to 10 ray flowers surrounding a raised central disc), but yellow or orange.
You’ve probably seen chocolate cosmos in garden centers: it’s been available for decades, showing up every now and then, usually in the form of tuberous roots offered for sale with other summer bulbs (dahlias, gladioli, cannas, etc.), more rarely in the form of a blooming plant.
Extinct in the Wild
Chocolate cosmos is said to have been introduced by William Thompson, founder of the renowned Thompson & Morgan seed company, back in 1902, from seeds harvested from the wild in the Zimapán region of the state of Hildago, Mexico. It has never been found since and is now considered extinct in the wild.
With its sweet and intriguing fragrance, chocolate cosmos quickly became a popular garden plant in Europe early in the 20th century, but like so many other plants, essentially disappeared from culture during the First World War. If it even survives today, it was because horticulturists at Kew Gardens, the famous British botanical garden, managed to keep a single clone alive right through the war. Until recently, therefore, all the chocolate cosmos grown anywhere in the world came from this single clone. And that causes a problem.
You see, chocolate cosmos, like so many plants, is self-sterile: it will not produce fertile seeds when pollinated with its own pollen. Since all the plants in cultivation were identical (they all derive by vegetative propagation from Kew Gardens’ single surviving specimen), pollinating flowers was a waste to time. No viable seeds could be produced. So for almost 100 years, all chocolate cosmos plants were clones produced by division or micropropagation and considered sterile. There was no way of producing better quality cultivars, notably ones with more flower power.
A Surprise From Down Under
Given that the one existing clone of chocolate cosmos was considered self-sterile, it was quite a surprise to learn that hybrids with superior flowering traits were being produced in New Zealand. Back around 1990, it would appear a single plant produced a few fertile seeds. The plants resulting from these seeds were no longer clones, but varieties with their own DNA. The differences between them may have been minor, since they all came from a single mother, but nevertheless each seedling was sufficiently different that they could cross readily with other plants. A first cultivar, Cosmos atrosanguineus ‘Pinot Noir’, was released locally by Russell Poulter in 1996, followed by others, although none attracted much international attention.
That has now changed. Hybridization programs continue in New Zealand and now also in Germany and Japan and new cultivars that are more floriferous and easier to grow are being released. There are now at least 4 cultivars raised by tissue culture that are available to gardeners in Europe: ‘Choca Mocha’ or ‘Chocamocha’ (30 cm), ‘Dark Secret’ (50 cm), ‘Eclipse’ (45 cm) and ‘Spellbound’ (60 cm).
North American gardeners will find it easiest to get their hands on ‘Choca Mocha’. It’s a dwarf variety 30 cm tall and is offered by Proven Winners. It came out last year in limited distribution and will be more widely available in 2017. That still doesn’t mean it will necessarily make it to your local garden center right away, though, so you might want to consider ordering it by mail order from nurseries like Phoenix Perennials in Canada and Burpee in the United States.
Or Raise It From Seed
Seeds of fertile varieties of cosmos chocolate are now available as well. Jelitto Perennial Seeds, a German wholesale seed supplier, introduced their seed strain, ‘Black Magic’, claimed to be the result of 10 years of hybridizing, in 2016. It’s now available from Chiltern Seeds and other seed companies… although it’s very expensive. The plants will be variable, with large or small flowers, rounded or notched rays, broad or narrow rays, various shades of dark red, a chocolate or vanilla fragrance and a height of between 1 and 2 feet (30–60 cm).
Of course, once you’ve found a plant that suits your needs, you can simply multiply it by dividing the tuberous roots each spring.
Chocolate cosmos is easy to grow from seed. Just start it indoors like any cosmos, about ¼ inch (5 mm) deep, 4 to 6 weeks before there is no longer any danger of frost in your area and grow in bright light to full sun under normal indoor temperatures.
In the Garden
Plant chocolate cosmos outdoors in full sun or partial shade in any well-drained soil, spacing the plants 12 to 16 inches (30-40 cm) apart. It grows well both in the garden and in containers. It needs no special summer care except watering during periods of drought. You’ll find it will bloom best if you deadhead regularly.
Since this plant is not cold hardy (zones 10 to 11), you can either consider it to be an annual and let it freeze or bring the tuberous roots indoors in the fall, treating them in the same way would dahlia tubers, that is, storing them dry in a cool spot. The two tubers are, in fact, actually very similar in appearance.
I can guarantee one thing: unlike real chocolate, chocolate cosmos is absolutely nonfattening!