ZINNIA, in botany, a genus of the natural order Compositae, containing about a dozen species of half-hardy annual or perennial herbs or under shrubs, natives of the southern United States and Mexico. The numerous single and double garden forms are mostly derived from Zinnia elegans, and grow about 2 ft. high, producing flowers of various colours, the double ones being about the size of asters, and very handsome. The colours include white, yellow, orange, scarlet, crimson and purple. Zinnias do best in a rich deep loamy soil, in a sunny position. They should be sown on a gentle hotbed at the end of March or in April and planted out early in June.