Zinnia

Sowing: Zinnia is raised from seed sown directly outdoors after the danger of frost has passed, or started indoors a few weeks earlier and transplanted out once nights are reliably warm; seed germinates in about a week at 70–75°F, and the first blooms appear roughly six weeks after sowing.

Siting and care: Plant in full sun in average, well-drained, fertile soil with good air circulation, and keep young plants evenly moist until they are established. Flower bud formation is triggered as day length shortens, so stem length and flower size increase with longer days and warmer temperatures, with bloom peaking once daylight falls below about 14 hours; regular deadheading and pinching back young plants encourages branching and prolongs flowering.

Spacing and support: Closer in-row spacing reduces side branching and suits a single concentrated harvest, while wider spacing between rows allows repeated cutting over the season; taller types benefit from wire or mesh netting to keep the stems upright. Drip irrigation is preferred over overhead watering, which can spot the petals, splash soil onto the foliage, and spread disease.

Several fungal and bacterial leaf diseases affect zinnia, especially in warm, humid, or wet conditions with poor air movement: alternaria leaf spot causes reddish-brown, pale-centered lesions that can encircle stems and cause wilting; bacterial leaf spot produces small translucent, yellow-edged spots that enlarge and can disfigure the flower heads; botrytis brings on a gray mold on flowers and stems in cool, wet weather; and powdery mildew coats the upper leaf surface in humid weather, often appearing late in the season and causing leaves to curl. Aster yellows, a virus-like disease spread by leafhoppers, stunts plants and produces distorted, greenish petals. Good air circulation, avoiding overhead watering, removing infected plant material, and rotating planting sites are the shared ways of limiting these problems.

Common pests include aphids, Japanese beetles, spider mites, and parasitic nematodes, while oedema is a recognized physiological disorder of the foliage.

Cut-flower stems are harvested once the blooms are fully open, ideally during cool periods such as early morning or evening, leaving two to three leaf pairs on the stem. Zinnias are not sensitive to ethylene, so they can be stored alongside other cut flowers, and stems placed promptly in a fresh flower food solution with about 1 percent sugar, held cool and shaded, and refrigerated at 38–42°F will keep for up to seven days, giving a vase life of roughly 7–10 days; stems affected by vascular bacterial stem blight should be discarded, as they shorten this postharvest life.

For drying, stems are cut in the same way once the heads are fully open, with foliage removed if the flowers will be processed right away. Most colors dry well using a desiccant such as silica gel, borax, sand, or cornmeal, though dark reds and scarlets tend to darken toward black-red as they dry.

Ornamental: Zinnia is grown chiefly as a garden and landscape ornamental, used in borders, mass bedding, containers, and meadow plantings, and its flowers attract butterflies, hummingbirds, and songbirds while being resistant to deer and rabbits.

Cut flower: Because of its long-lasting blooms and non-sensitivity to ethylene, zinnia is widely grown as a cut-flower crop for fresh arrangements, and its flowerheads are also dried for use in preserved floral work.

Zinnia's cultivated forms descend from wild species native to Mexico and adjacent parts of southern North America, with the genus's diversity centered in Mexico. Zinnia elegans was brought into cultivation by the Spanish botanist Casimiro Gómez de Ortega, who established the botanical garden in Madrid, and in 1796 he sent seed to England, from where the plant entered European gardens and gained popularity from around the 1790s onward. Through the early and mid-1800s, gardeners on French, Flemish, and English estates further developed the flower, and a naturally occurring double-flowered form discovered in a seed lot from the West Indies was introduced to the trade, cementing zinnia's place as a garden flower before it later fell in and out of fashion.