This section is from the book "Commercial Gardening Vol2", by John Weathers (the Editor). Also available from Amazon: Commercial Gardening, A Practical & Scientific Treatise For Market Gardeners.
This genus contains annual and perennial varieties. P. Drummondii and its numerous varieties are usually grown as half-hardy annuals, but they may also be sown in the open ground in March to flower during the summer months. Florists and seedsmen usually sell large quantities of seed in spring. Growers raise the plants in shallow boxes, and sell them from April to June for bedding purposes. The grandiflora forms are very popular, but there are others, such as alba, white; carnea, flesh; oculata, white with purple eye; Leopoldi, scarlet, white eye; cuspidata, starry petals; nana compacta, with blue and carmine forms.