Cosmos (Cosmos bipinnatus) is an annual flowering plant in the Asteraceae family.

• Cosmos are native to Mexico and may be perennial if the conditions are right.
• Cosmos readily self-seed, so beds may need thinning if the same site is used again.
• Cosmos flowers grow on long, narrow stems.   Branches have pinnate leaves.
• There are many hybrids and cultivars, providing a variety of colors and shades.
• Cosmos have a long growing season, producing many flowers on multiple stems.
• Cosmos can grow in a variety of soils and are relatively drought tolerant.
• Cosmos attract pollinators.   Cosmos are excellent for cut flowers.
• We plant cosmos at the back of flowerbeds or on narrow borders near a south-facing fence.    We have also had success in planting on borders near a slope break.

All photos by the author, taken in our gardens.   Click an image for a lightbox view and a caption.

cosmos

cosmos

cosmos

cosmos

cosmos

cosmos

cosmos

• We usually collect seed in the fall, then hand seed into a selected area after the last frost in the following spring.
• Cosmos will flower in about 7 weeks.
• Deadheading encourages more blossoms.
• We prefer to collect our own seed and deadhead the other spent flowers to avoid too much self-seeding.
• Spacing the plants close provides support for the long stems, but not too close together, making it hard to weed.   In windy spots, some staking may help.
• We rarely fertilize cosmos and never hand water them (we have irrigation).    We have rarely seen aphids or disease.    We think that planting them in sunny areas with good drainage helps.
• After the killing frosts, we uproot the plants, chop them up, and compost them, removing any mature seedheads.
• Cosmos can be seeded indoors, but it is very easy to grow with direct seeding so we have chosen to seed them directly into the garden.