How to prune chocolate cosmos

Deadhead throughout summer; cut back before lifting tubers in autumn. Remove each spent flower by cutting back to the nearest leaf or lateral bud. At the end of the season, cut stems to 2–3 inches before digging and storing tubers for winter.

Deadhead every few days in bloom; once-yearly end-of-season cutback. Chocolate Cosmos (Cosmos atrosanguineus) is a tender tuberous perennial that does not self-seed. Deadheading spent flowers keeps the plant blooming from midsummer until frost. Cut the whole plant down to a few inches before lifting tubers in autumn in frost-prone areas, or in late winter in mild climates.

Remove each spent flower by cutting back to the nearest leaf or lateral bud. At the end of the season, cut stems to 2–3 inches before digging and storing tubers for winter.