How to Plant, Grow, and Care for Zinnias
From watering tips to when to deadhead, we asked two gardening experts to share their advice.
If you're a fan of colorful, low-maintenance flowers, then you shoulder consider planting zinnias in your garden. "Zinnias are universal symbols of summertime that bloom from mid-summer until the first frost, in crisp, vibrant colors such as pink, red, orange, yellow, green, and white," says Venelin Dimitrov of Burpee. "The flowers bloom in a range of shapes, including quilled, dahlia-type, single, semi-double, and double flowers. Plus, they are excellent flowers for new gardeners and children to grow, as the seeds are large and easy to handle, and the flowers often attract many species of butterflies."
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Along with being beautiful and easy to grow, zinnias are also heat- and drought-tolerant. "They are great for hot summer weather and gardeners in warmer climates," explains Dr. Gladys Mbofung-Curtis, a garden expert at Garden Safe. "Zinnias are one of the easiest flowers to grow because seeds require only basic garden preparation to sprout and the plants flower in just a few weeks; they can flourish with very little fertilizer and still produce flowers."
Plant zinnias in full sun.
Zinnias thrive in full sunlight and should be planted at the beginning of the warm weather season. "They are short-day plants that flower when the day length is less than 11 hours, therefore they are perfect for early spring planting when the nights are longer," Mbofung-Curtis explains. "Zinnias grow and flourish well in full sunlight in cooler climates, but in warmer climates, occasional afternoon shade may help relieve the plants from the excessive heat."
Seed zinnias in moist soil.
In warm climates, zinnias should be seeded directly into the soil after any frost has passed, says Mbofung-Curtis; in cooler climates, seeds can be started indoors in germination trays. "Whether seeding directly in beds or germination trays, zinnia seeds should be sown to a depth of a quarter of an inch into deep, loamy soil," she says. "The distance between seeds or seedlings in the beds should be about six inches apart for good airflow and rows should be spaced 12 inches apart."
Even though zinnias can tolerate short periods of drought, Mbofung-Curtis says they'll grow best in moist soil. "Water plants about three times a week so that the soil stays moist to about six to eight inches deep," she advises. "Overwatering and continuous wet conditions can take a great toll, since high humidity can lead to development of powdery mildew, leaf spots, and rot, so water at the base of the plants." For potted plants, she recommends only watering them when the soil feels dry. "Avoid splashing the leaves as this may splatter spores of the fungus from the ground to the leaves."
Mulch makes a difference.
While zinnias can grow well in average soils, Mbofung-Curtis says they'll perform better with the help of compost, fertilizer, or mulch. "Once zinnias are established, mulching with a two-inch layer of straw or bark will help preserve soil moisture and prevent weed growth. In addition, a light fertilizer may be applied at the seedling stage. At flowering, side dressing with an organic 5-5-5 fertilizer will produce numerous and bigger blossoms. Zinnia seeds can also be sowed directly into one to two inches of organic mulch that will provide nutrients throughout the season as the mulch breaks down to form compost."
A little pruning can go a long way when growing zinnias in your garden. "When zinnias have grown to several inches, prune frequently to encourage more branches for flower head growth," Mbofung-Curtis says. "Rather than allowing flowers to be spent on the plants before deadheading, cut the mature flowers for use in bouquets to encourage blossoming throughout the season. Otherwise, just pinch spent blossoms off. However you maintain them, your zinnias will continue blooming to produce more and more flowers."