Answer: Zinnia elegans is the most well known of the 20 or so species in the zinnia genus. The wild form is a coarse, upright, bushy annual, to 30 in (76 cm) high, with solitary daisylike flowerheads on long stems, and opposite, sandpapery, lance shaped leaves. The ray flowers are purple, the discs yellow and black, and the entire head is about 2 in (5 cm) across. Gardeners love zinnias and there are at least a hundred cultivars in a diversity of flower colors and types, some with flowerheads up to 6 in (15 cm) across. There are zinnias with white, cream, green, yellow, apricot, orange, red, bronze, crimson, purple, and lilac flowers; zinnias with striped, speckled and bicolored flowers; zinnias with double, semi-double and dahlia-like "pompon" flowers; zinnias that range from dwarfs that don't exceed 6 in (15 cm) in height to cut flower beauties that get 3 ft (0.9 m) tall. Newer varieties are resistant to powdery mildew and other diseases. 'Old Mexico' is like the wild plant with single, daisylike flowerheads with wide purple rays.
The many garden forms of Zinnia elegans were developed from the wild plant that grows in Mexico. Common zinnia has escaped and naturalized in parts of the southern US, including central Florida.
Zinnias are easy to grow in well drained, rich loamy soil, in the open with full sun. Provide full sun for most cultivars. The pale green cultivar, 'Envy' tolerates light shade. Zinnias do best in well drained soil with infrequent watering. They are quite drought tolerant. Zinnias may become infected with powdery mildew in humid climates, especially if they don't have good air circulation all around them.
Hardiness: Zinnias are warm weather annuals. They do best in climates with long, hot, dry summers. Zinnias do not tolerate frost.
Propagation: Sow seeds where the plants are to be grown in spring after the last frost, or set out 6-8 week-old seedlings. Zinnias are sensitive to root disturbance, so be especially careful when transplanting.
Zinnias are traditional in annual flower beds and borders. Use the dwarf varieties in containers and window planters. Grow the taller varieties in borders and beds and for cut flowers. Pinch young stems back to encourage branching unless growing for long-stemmed cut flowers. Deadhead spent flowers frequently to prolong flowering. Zinnias will produce larger (but fewer) flowers if you remove side shoots.
Zinnias are among the few bedding plants that will continue to perform through hot southern summers, all the way up to the first frost. And, they are available in a riot of colors to satisfy any garden plan!
Apparently Zinnia violacea is an older name used for this species in 1791 that some taxonomy purists now insist on using. But I will stick with the well known Zinnia elegans until they pry this keyboard from my cold dead hands.
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