Cosmos Companion Plants
Flower70 days to maturity
Cosmos (Cosmos bipinnatus) are airy, daisy-flowered annuals that bloom prolifically on tall, feathery stems from summer to frost. They thrive in poor, lean soil, since rich ground produces lush foliage but few flowers, which makes them easy to tuck among vegetables. Their nectar-rich blooms attract pollinators and predatory insects like lacewings and parasitic wasps that hunt aphids.
Companion Checker: what grows well with Cosmos?
Tap any plant to see whether it pairs well with Cosmos and why. Green means a beneficial companion, red means keep them apart.
Want to lay out a whole bed? Open the full drag-and-drop companion planting tool →
Companion Planting Strategy for Cosmos
Cosmos work as a low-maintenance insectary flower, attracting pollinators along with lacewings, hoverflies, and parasitic wasps that prey on aphids and other soft-bodied pests. Because they thrive in poor soil and do not compete heavily for nutrients, they are easy to interplant with vegetables without robbing them.
Best Companion Plants for Cosmos
These plants grow well alongside Cosmos — providing pest control, attracting pollinators, or making better use of your garden space.
Cosmos attract hoverflies, lacewings, and parasitic wasps that prey on aphids and tomato hornworms, while also drawing pollinators that improve fruit set.
Cosmos pull in beneficial predators that control aphids and leaf miners on beets, and their airy habit does not crowd the low foliage.
Cosmos lure the pollinators cucumbers need for fruit set and host predators that feed on aphids and cucumber beetles.
How to Grow Cosmos
- Botanical name
- Cosmos bipinnatus
- Family
- Aster/Daisy (Asteraceae)
- Sun
- Full sun, 6 or more hours daily
- Water
- Low; about 1 inch per week, drought-tolerant once established and dislikes overwatering
- Soil
- Light, well-draining, lean soil, pH 6.0-7.0; avoid rich soil, which reduces blooms
- Spacing
- 12-18 inches apart
- Planting depth
- Sow seed 1/4 inch deep
- Germination
- 7-21 days at 70-75F
- Days to maturity
- 50-90 days from seed to first bloom depending on variety
- When to plant
- Direct-sow after the last frost once the soil is warm
- Harvest
- Blooms early summer to frost; cut flowers as they open and deadhead regularly to keep new buds coming
Common Cosmos Problems
Floppy, leggy plants that fall over
Pinch young plants to encourage branching, stake tall varieties, and avoid rich soil and excess fertilizer, which produce weak, overgrown stems.
Few flowers despite lush foliage
Caused by soil that is too rich and too much nitrogen. Grow cosmos in lean, well-draining soil, hold back on fertilizer, and give them full sun.
Aphids on stems and buds
Spray them off with water and let the lacewings and ladybugs the flowers attract finish the job; use insecticidal soap if needed.
Powdery mildew and gray mold (botrytis)
Space plants for airflow, water at the base, and remove faded blooms and affected foliage promptly in damp weather.
Cosmos Companion Planting FAQ
What are the best companion plants for cosmos?
Cosmos pair well with tomatoes, beets, and cucumbers, attracting pollinators for better fruit set and predatory insects like lacewings and parasitic wasps that hunt aphids. Their light, airy habit means they do not crowd out neighboring crops.
What should you not plant with cosmos?
Cosmos have no notable bad companions and grow harmoniously with most vegetables and flowers. Just avoid placing them where their tall stems will shade out shorter, sun-loving crops.
Why are my cosmos not flowering?
Too-rich soil and excess nitrogen push cosmos to grow tall and leafy at the expense of blooms. Plant them in lean, well-draining soil, go easy on fertilizer, and make sure they get full sun to encourage flowering.
Do cosmos need full sun?
Yes, cosmos bloom best in full sun with at least six hours of direct light daily. In too much shade they grow leggy and flower poorly, and they may need staking to stay upright.
More flower companions
Plan Your Cosmos Garden
Use our interactive tools to design the perfect garden with Cosmos and its companions.