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Common Cosmos, Mexican Aster 'Seashells'

Cosmos bipinnatus

Family: Asteraceae (ass-ter-AY-see-ee) (Info)
Genus: Cosmos (KOS-mus) (Info)
Species: bipinnatus (by-pin-NAY-tus) (Info)
Cultivar: Seashells
Additional cultivar information:(aka Sea Shells, Sea Shells Mixture)



Foliage Color:


Bloom Characteristics:

This plant is attractive to bees, butterflies and/or birds

Water Requirements:

Drought-tolerant; suitable for xeriscaping

Average Water Needs; Water regularly; do not overwater

Where to Grow:

Unknown - Tell us


24-36 in. (60-90 cm)

36-48 in. (90-120 cm)


18-24 in. (45-60 cm)


Not Applicable

Sun Exposure:

Full Sun


Parts of plant are poisonous if ingested

Bloom Color:



White/Near White

Bloom Time:

Late Spring/Early Summer

Mid Summer

Late Summer/Early Fall

Mid Fall



Other details:

Unknown - Tell us

Soil pH requirements:

6.6 to 7.5 (neutral)

7.6 to 7.8 (mildly alkaline)

7.9 to 8.5 (alkaline)

Patent Information:

Unknown - Tell us

Propagation Methods:

From seed; sow indoors before last frost

From seed; direct sow after last frost

Self-sows freely; deadhead if you do not want volunteer seedlings next season

Seed Collecting:

Allow seedheads to dry on plants; remove and collect seeds

Properly cleaned, seed can be successfully stored


This plant has been said to grow in the following regions:

Lawndale, California

San Leandro, California

Barbourville, Kentucky

Provincetown, Massachusetts

Saint Paul, Minnesota

Dolgeville, New York

Elizabeth City, North Carolina

Toledo, Ohio

Portland, Oregon

Warwick, Rhode Island

Leesburg, Virginia

Kalama, Washington

Black Earth, Wisconsin

show all

Gardeners' Notes:


On Jul 19, 2012, BlackEarthSquid from Black Earth, WI wrote:

Planted on May 14, after an exceedingly hot/dry summer I have 5-6 foot stalking green fringy plants, but no flowers yet. I have been told this is normal. I believe they will bloom later this summer (it is only July 19). The soil here is very rich and I have been told this also contributes to big stalks/lots of leaves/fewer blossoms.

They are enormous and tower over everything else in the garden, I am hoping I get some blooms out of them! If i had known how tall they were going to be, I'd have put them on the back border. But the package said, "36 inches" ha!

Next year I will throw seeds on the ground in poor soil, kick dirt on them and walk away :*) seems to be the advice I am gleaning from other Cosmos fans.


On Aug 30, 2010, sketchkat06 from Lawndale, CA (Zone 10a) wrote:

These turned out really well in my parent's garden! I got tired of the same old common single variety and found these. Glad to find they are as tall and covered in blooms as the common variety. The tubular shape of the petals makes them look nice and frilly from a distance. Had a few odd balls that didn't tube, but came out in an almost double lacy form.

They did end up with some powdery mildew that didn't go away with baking soda spray :/ but that hasn't seemed to really damage it all. I dead headed for awhile until they got to thick to get at. The plant does look a bit raggedy as the blooms fade and it starts really setting see. Also I recommend staking, they will lean in the direction of the sunrise.


On Jul 5, 2009, lehua_mc from Portland, OR (Zone 8b) wrote:

I needed something that would be a tall screen, and I got it with the Seashell mix! The Ed Hume package told the truth, they really do get about 5' tall, with massive 1" thick stalks nearing their base. I found mine did not bud until late summer or flower until fall (October/November). I believe that due to the late flowering, it did not set seed, and therefore I have no volunteers this spring.
A heat spike during the summer caused these giants to fall over dramatically (and somewhat devastatingly for anything smaller). Not the kind of plant to give up once prone, it continued to grow in a contorted tangle skywards. Word to the wise, establish a staked barrier early.


On Mar 4, 2007, berrygirl from Braselton, GA (Zone 7b) wrote:

Also known as 'Sea Shells Mixture'.
Exotic tubular flowers in shades of pink, red, and white. A real eye-catcher in any garden. Extremely easy to grow from seed. Half-hardy annual, 4-5 ft tall.