Cosmos bipinnatus, commonly called Garden Cosmos or Mexican Aster, is a medium sized flowering herbaceous plant native to the Americas, most notably Arizona, Mexico, Guatemala, and Costa Rica. The species and its varieties and cultivars are popular as an ornamental plant in temperate climate gardens. It can also be found in natural area in much of North America, where it is a garden escape (introduced species) and in some habitats becoming a weed. Due to its use as an ornamental plant in many countries and prone to sedimentation, it is considered an invasive plant in many areas of the world. It has naturalized in scattered locations across North America, South America, the West Indies, Italy, Australia, and Asia.
Cosmos bipinnatus is considered a half-hardy annual, although plants may reappear via self-sowing for several years. The plant height varies from .61 - 1.8m, and rarely to 2.7m. The cultivated varieties appear in shades of pink and purple as well as white. The branched stems is usually densely to occasionally occupied by fine, split up, rough trichomes; though some species are completely hairless. The petiole itself if inconspicuous, winged, and 10-15mm long. Its foliage is finely cut into thread-like segments. The flowers have a diameter of 5-8cm and are both tongue and tubular shaped, surrounded by bracts. The inner and outer bracts are ovate to lanceolate shaped, with the outer bracts measuring 7-15mm long and 3-6mm wide and the inner bracts measuring 8-12mm long. The sprout leaves have gold-yellow, thread-like tips and protrude between the tubular flowers. The broadened base of these spreader leaves is translucent with a yellow line. When flowering, the plant can become top heavy. This problem is alleviated when grown in groups, as the bipinnate leaves interlock and the colony supports itself. The flowers may show noticeable stains at the base causes by anthocyanin.
Germination of Cosmos bipinnatus usually takes place between 7 and 10 days at the optimal temperature of 75 degree Fahrenheit, with flowering starting between 60 and 90 days after germination. It prefers a soil pH between 6.0 and 8.5, reflecting its native habitat in the alkaline regions of Central America. Flowering is best in full sun, although partial shade is tolerated. Excessive rain can cause cultivation problems, due to the delicate nature of the stems, and heavy rain can cause breakage. Cosmos bipinnatus can tolerate heat as long as adequate moisture is provided, however, it does not handle droughts, strong winds, or cold temperatures well. Snails, slugs, and aphids have a taste for Cosmos bipinnatus. The flowers of Cosmos bipinnatus attract many pollinators, including the Monarch Butterfly. It can be used in butterfly gardening, as well as pollinator/honey-bee habitat gardens.
Some common cultivars of Cosmos bipinnatus include "Apollo" (pink, carmine, and white), "Daydream" (has a pink inner ring on a white background), "Double Click" (features semi-double to fully double flowers that resemble Japanese anemones), "Rubenza", "Sensation" or "Early Sensation", "Sonata", "Velouette", "Versailles", many of which have earned the Royal Horticultural Society's Award of Garden Merit.
Article excerpt is from Wikipedia.org under the Creative Commons License
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