Cosmos create an abundance of brightly colored, daisy-like flowers atop slender stems. With over 20 species of the striking flowers, “Cosmos sulphureus” and “Cosmos bipinnatus” would be the most usual annual varieties grown in the USA. Others, like the chocolate cosmos (Cosmos atrosanguineus), are perennials in U.S. Department of Agriculture plant hardiness zones 9 and 10.
“Cosmos sulphureus” creates yellow, orange, red or golden flowers. Frequent varieties include “Bright Lights,” “Cosmic Yellow” and “Crest Red.” Flowers may be either single or double blooms and come in a variety of sizes from dwarfs to plants 3 to 4 feet tall. Foliage on those plants is lobed with hairy edges.
“Cosmos bipinnatus” produces blossoms similar to other varieties, in the white, white, pink and increased range. Foliage is fernlike, giving the cosmos an airy look as the blooms sway in the summer breeze. Height ranges from 1 to 6 feet, depending on the cultivar. Frequent varieties include “Seashell Mix,” “Daydream” and also the “Sensation” series.
“Cosmos atrosanguineus,” known as chocolate cosmos, creates lightly fragrant blossoms that produce a chocolate or vanilla scent. Blooms consist of single petals that are nearer to “oxblood red” than brown. These tuberous root cosmos develop as perennials in USDA plant hardiness zones 9 and 10. In USDA zones 8 and below, the tubers must be raised in the autumn and replanted in the spring.
Because cosmos frequently self-seed, annual varieties might come back after their first year, giving the appearance of being perennials. When permitted to self seed in an undisturbed place, cosmos may produce well for many years without replanting.
Cosmos are tolerant of a wide range of growing conditions, such as poor soil and drought. They produce appealing backgrounds, additions to meadow gardens or boundaries to walkways. These flowers attract butterflies into the garden as well.