How to Grow Chocolate Cosmos

Deep red petaled flower with brown spiky center, green background
The deep red tones on chocolate cosmos have a velvety look and feel

Sandra Király / Flickr / CC BY 2.0

These unusual flowers look like regular cosmos but are a bit smaller, measuring an inch and a half across, and the petals are rounded. They have a dark rich maroon color with a distinct velvety appearance—and they smell like chocolate (really!). This highly-sought after flower was first introduced commercially in 1885, in a seed catalog. However, the seeded varieties are rarely available, and so these cosmos are mostly propagated via tuberous roots, similar to the roots of dahlias. The centers are dark brown and the overall effect is very dramatic, making these flowers highly sought after for thrilling garden beds, containers, and floral arrangements. They pair especially well with all shades of pink flowers, creamy white flowers, and blue shades to offset the brown tones. They make marvelous cut flowers too, holding up well for days. This plant has been rumored to be extinct in the wild for decades, but in the early 21st century Mexican botanists did field work to confirm its presence in old oak and pine forests. In recent years, several new cultivars have been introduced.

The chocolaty fragrance of chocolate cosmos is due to the presence of vanillin, an organic compound also found in cocoa. The scent is most pronounced on warm days. Planting them in containers near a patio or seating area allows you to enjoy the fragrance more easily.

Botanical Name Cosmos atrosanguineus 
Common Name  Chocolate Cosmos 
Plant Type  Annual, perennial above Zone 7 
Mature Size  30 in. tall
Sun Exposure  Full sun
Soil Type  Rich, well drained 
Soil pH  Slightly acidic 
Bloom Time Summer 
Flower Color  Dark red
Hardiness Zones 7-11 (USDA)
Native Areas  Mexico
Toxicity  No toxic effects reported
Deep brownish red flowers with rounded petals in a green meadow setting
The distinctive color of these cosmos really pops alongside the greens of the summer garden

David King / Flickr / CC BY 2.0

Chocolate Cosmos Care

These flowers behave much like regular cosmos despite their differences. They benefit from deadheading to keep the blooms looking neat, and will usually keep producing new flowers until the first frost. They're hardy as perennials in Zones 9 and above, but with heavy mulching and winter protection, you may have luck growing them as perennials in Zones 7 and 8. These flowers may take a couple of years to get established, but as the plants increase in size they will produce more flowers in season. They can be divided in spring or autumn.

Light

Like regular cosmos, chocolate cosmos like plenty of direct sunlight, at least six hours per day.

Soil

Well-drained, fertile soil will allow these beauties to flourish. If growing in containers, a mix of potting soil and topsoil should yield good results, perhaps adding some pebbles in the bottom of the container to ensure good drainage.

Water

Too much water can cause their roots to rot, so be careful not to overwater. A deep watering once per week in summer, unless there is a lot of rain, should be sufficient. Allow the soil to dry out slightly between waterings.

Temperature and Humidity

These flowers can be frost sensitive, so beware of planting before all danger of frost has passed. They can handle humidity and enjoy moist soil, but too much water at their roots can cause rot.

Fertilizer

Too much fertilizer might cause your chocolate cosmos to produce more foliage than blooms, but a bit of rose food applied in spring can help these flowers achieve and maintain their vibrant color through to autumn.

Are Chocolate Cosmos Toxic?

These flowers have no reported toxic effects in humans or animals.

Propagating Chocolate Cosmos

The seeds of chocolate cosmos are sterile, so they won't reseed or produce plants from seed. The only way to propagate these flowers is via a root cutting or planting. The roots are thick and tuberous; look for root sections that have "eyes" or buds of new growth for the most successful plant starts.

Overwintering

Chocolate cosmos are grown as an annual in colder climates, but the roots may be dug up in autumn and stored for winter as you'd store any other root annual such as a canna or dahlia, and replant them in spring. In warmer climates where they stay planted year round, give them a good coating of natural mulch to protect the roots for winter.

Common Pests and Diseases

The following problems may plague your chocolate cosmos: Powdery mildew, stem canker, Rhizoctonia stem rot, gray mold, and aphids. Give them plenty of space and air flow to prevent powdery mildew.