Chocolate Cosmos are half hardy and can tolerate temperatures to -5C. In mild or coastal areas they can usually be planted directly outside in spring, but it is safer to start them off in sheltered conditions.
— Plant your tubers into temporary pots in spring and grow-on in a sheltered spot outdoors or in a cool greenhouse – they can be transplanted into the garden after May. Alternatively, plant the tubers directly into a clear, cultivated space in borders in late April to early May.
— Dig a whole to the same depth as the tubers so that they are planted with the crown just below the soil surface. Any shoots can be partially covered, or if they already have some leaves emerging this can be left exposed.
— Choose a location in full sun or partial shade with rich but free-draining soil.
— Space the plants 25-30cm apart
— Water-in after planting and keep hydrated when in growth.
— Cut back stems and foliage to 3cm above ground level in autumn. The tubers can be lifted and stored in temporary pots through winter, in frost free-conditions.