Zinnia

Zinnias resent transplanting and perform best when direct sown into warm garden soil after the last frost. Prepare the bed by working in a two-inch layer of compost and rake smooth. Sow seeds a quarter inch deep and keep moist until germination, which takes five to seven days in soil above 70 degrees Fahrenheit.

Thin seedlings to their final spacing once they have two sets of true leaves: four to six inches apart for dwarf types, twelve to eighteen inches for tall cut-flower varieties. Pinch the growing tip of each seedling when it reaches about twelve inches tall to encourage branching and more flower stems.

Water zinnias at soil level using drip irrigation or a soaker hose, as wet foliage invites powdery mildew. Feed every three to four weeks with a balanced fertilizer or top-dress with compost. Remove spent flowers by cutting the stem back to just above a leaf node, which triggers new branching and prolongs the bloom season well into fall.

Zinnia elegans is native to the semi-arid grasslands and scrubby hillsides of central and southern Mexico, where wild populations still grow today in the states of Durango, Jalisco, and Oaxaca. The Aztec people were familiar with the plant but considered the small, purplish-brown wildflowers unremarkable in appearance, reportedly calling them by a name that translates roughly to 'eyesore' or 'plants that are hard to look at.' Spanish conquistadors and early botanists collected specimens during the colonial period, but zinnias initially failed to impress European gardeners when seeds were first sent to the Royal Botanic Garden of Madrid in the early 1700s. The genus was formally named by Carl Linnaeus in 1759 in honor of Johann Gottfried Zinn, a German botanist and physician from the University of Gottingen who had published detailed descriptions of the plant. Through the late 18th and 19th centuries, European plant breeders began selecting for larger flowers, doubled petals, and brighter colors, gradually transforming the humble Mexican wildflower into the vibrant garden ornamental we recognize today. By the early 20th century, American seed companies had embraced the zinnia as a staple of summer flower gardens across the United States. Luther Burbank and other notable breeders worked to develop the giant dahlia-flowered types that became enormously popular in the 1920s and 1930s. Today, Zinnia elegans and its hybrids are among the most widely grown annual flowers in the world, cultivated on every inhabited continent in home gardens, commercial cut flower operations, and public landscapes. Modern breeding programs continue to release new varieties with improved disease resistance, compact habits for container growing, and novel color combinations that would have astonished the Aztec farmers who first overlooked this now-beloved flower.

Zinnias prefer average to rich, well-drained soil with a pH between 5.5 and 7.5. Amend heavy clay soil with compost and coarse sand to improve drainage, as zinnias are susceptible to root rot in waterlogged conditions. Apply a balanced 10-10-10 granular fertilizer at planting and again when buds begin to form. For continuous-bloom varieties, feed every three weeks with a diluted liquid fertilizer. Too much nitrogen results in abundant foliage with fewer flowers.

Cut zinnia stems for bouquets when the flower is about three-quarters open and the stem feels firm when you wiggle it. A limp stem indicates the flower will not take up water well and will wilt quickly. Cut in the early morning, making a clean diagonal cut and placing stems immediately in water. For seed collecting, allow flower heads to dry fully on the plant until petals are papery, then pull individual seeds from the center cone and store dry.

Fresh zinnias last seven to ten days in a clean vase with floral preservative. Recut stems and change water every two days for maximum longevity. To dry zinnias, cut flowers at peak bloom and hang upside down in small bunches in a dark, warm, well-ventilated area for two to three weeks. Zinnias can also be pressed between sheets of parchment paper under heavy books for use in crafts. Dried zinnia petals retain their color better than most flowers.