Cosmos can be “blooming fools” in a summer garden, but sometimes all that showing off poops them out, and they turn brown and start to shrivel later in the summer. That can leave a gap in the garden (which I detest). For that reason I never plant cosmos in a large mass.
I’ve tried many cultivars over the years and most of them eventually look like this at some point in the summer, even if I fertilize and deadhead the plants regularly:
However, when they are healthy and in full bloom, cosmos are a lovely sight to behold.
My favorite cosmos are the Sonata series, especially ‘Sonata Carmine’ and ‘Sonata Pink Blush’ (seen below in that order). The flowers are large—up to several inches in diameter—and their color is rich:
Sonata cosmos grow 24 inches tall and bloom on delicate, lacy foliage that reminds me of dill.
They’re best sown directly into the garden, but you can start them indoors about 4 weeks before the last frost date. You just have to watch the indoor-reared plants carefully or they grow too quickly and get leggy and floppy before you’re ready to plant them in the garden.
The plants shrug off heat and drought and prefer growing in full sun, although they will tolerate partial-shade.
If someone could create a cultivar that would continue blooming all summer into fall without turning brown or shriveling, it could quickly become the perfect annual.