Sow indoors for surest results, 0.5cm (¼”) deep, in trays of compost. Water well and place in a cold frame, unheated greenhouse or on a cool windowsill. Seedlings appear in 14-42 days. Transplant seedlings 5cm (2”) apart to further trays when large enough to handle. (Always handle by a leaf, never by the stem.) Gradually accustom young plants to outside conditions (avoid frosts) before planting out 40cm (16”) apart.
Sow outdoors in a seed bed, 0.5cm (¼”) deep into finely prepared soil which has already been watered. Thin seedlings to 5cm (2”) apart before planting out to flowering positions in spring or autumn, spacing 40cm (16”) apart.