Diablo Cosmos is a showstopping annual flower that brings deep, sultry color to summer gardens across zones 2 through 11. This cultivar of Cosmos sulphureus grows to a substantial 48 to 60 inches tall, creating dramatic vertical interest with its striking blooms. It thrives in full sun and handles the heat with ease, making it a reliable performer from early summer through frost. The plant's frost-tender nature means it's best sown after your last spring frost, but gardeners in colder zones can start seeds indoors 4 to 6 weeks earlier for a head start on the growing season.
Full Sun
Moderate
2-11
60in H x ?in W
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Moderate
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Diablo Cosmos delivers bold, deep-colored flowers on tall, airy plants that cut through summer gardens with real presence. The cultivar reaches upward to five feet, providing vertical drama without heavy, woody stems. Starting from seed is straightforward: sow outdoors once soil warms to at least 60 degrees Fahrenheit, or begin indoors a month or so before your last frost for earlier blooms. These plants demand full sun and well-draining soil with a pH between 6.0 and 7.5, and they reward minimal fussing with prolific flowering until frost arrives.
Diablo Cosmos is grown as an ornamental flowering plant, prized for cutting and garden display. The tall stems and abundant blooms over many weeks make it especially valuable for fresh arrangements and for filling gaps in mixed borders where height and color are needed.
No timeline data available yet for this variety.
Start seeds indoors 4 to 6 weeks before your average last frost date. Sow seeds so they are barely covered, and maintain a germination temperature of 60 degrees Fahrenheit.
Transplant seedlings outdoors 4 to 6 weeks before your average last frost date if starting indoors. Alternatively, wait to transplant or direct sow until 1 to 2 weeks after your average last frost date, when soil temperature is at least 60 degrees Fahrenheit.
Sow directly outside 1 to 2 weeks after your average last frost date, when soil temperature is at least 60 degrees Fahrenheit. Barely cover the seeds.
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