There is one kind of annual cosmos (Cosmos sp.) that does very well for us. These are not delicate plants and, even with our sometimes miserly allocation of water, they manage to survive the hot summer to bloom profusely during the fall. These plants have very fine, feathery leaves, reminiscent of marigolds. The color of the blossoms is a consistent bright orange to deep gold, but the height of the plants varies considerably. Ours grow from one to three feet tall, but at a nearby botanical garden, with plenty of water, fertilizer and mulch, these same flowers attain a height of about eight feet. The seeds produced are long and slender and birds love them, often picking the seed heads clean.
The blossoms last several days as the central disk flowers open in sequence. The outer petals start out in a cup form, but eventually open flat.