How to Grow and Care for Zinnias, an Easy Flower That Blooms All Summer

If you're a fan of colorful, low-maintenance flowers—and who isn't?—then zinnias are a foolproof choice for your garden. These brightly-hued annuals require little effort to grow and provide a steady supply of pretty blooms to cut and display in your home.

Along with being beautiful and easy to grow, zinnia flowers are also heat- and drought-tolerant. "They are great for hot summer weather and gardeners in warmer climates," says 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."

Keep reading for our expert advice on how to grow and care for your zinnias so you, too, can enjoy their vibrant display.

Varieties of Zinnias

Plants in the zinnia genus are members of the Asteraceae family, which also includes daisies and asters. "The flowers bloom in a range of shapes, including quilled, dahlia-type, single, semi-double, and double flowers," says Venelin Dimitrov of Burpee. "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."

According to Sabrina Schirtzinger, extension educator at Ohio State University, some of the most common zinnia varieties grown in backyard gardens include:

• Benary Giant: These large, eye-catching double flowers grow up to 39 inches tall in about nine weeks.
• Oklahoma: Oklahoma zinnias can be double or semi-double blooms and boast a range of hues that include dusty pink, bright gold, and regal purple.
• Cactus: Instead of the rounded shape of other zinnias, the Cactus variety boasts spiky petals on 5-inch-wide blooms that sit atop 3-foot-tall stems.
• State Fair: Disease-resistant State Fair zinnias grow up to 6 inches across and come in vivid, warm shades ranging from pink to yellow.

Schirtzinger admires the flower for its wide variety of colors, sizes, and shapes—as well as its fast, reliable growth habits, low-effort care requirements, and sturdy stem (perfect for harvesting). "Zinnias are dependable, low-maintenance, and have vibrant colors!" she says. "For a constant cut flower supply, plant in succession by sowing every two weeks."

How to Grow Zinnias From Seed

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 1/4-inch into deep, loamy soil," she says. "The distance between seeds or seedlings in the beds should be about 6 inches apart for good airflow, and rows should be spaced 12 inches apart."

She adds that zinnia seeds can be sowed directly into 1 to 2 inches of organic mulch that will provide nutrients throughout the season as the mulch breaks down to form compost.

How to Care for Zinnias

As annuals, zinnias grow quickly but only last for a single season. Here's how to tend to this beautiful flowering plant.

Sunlight

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 says. "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."

Watering

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 6 to 8 inches deep," she says. For potted plants, she recommends only watering when the soil feels dry.

Soil

These plants prefer well-drained, neutral, or slightly acidic soil with a pH between 5.5 and 7.5. "Once zinnias are established, mulching with a 2-inch layer of straw or bark will help preserve soil moisture and prevent weed growth," says Mbofung-Curtis.

Fertilizer

While zinnias can grow well in average soils, Mbofung-Curtis says they'll perform better with the help of compost or fertilizer. "A light fertilizer may be applied at the seedling stage," she says. "At flowering, side dressing with an organic 5-5-5 fertilizer will produce numerous and bigger blossoms."

How to Prune Zinnias

A little pruning can go a long way when growing zinnias in your garden. "The more you cut zinnia blooms off, the more flowering will occur," says Schirtzinger. "Pinch zinnias when the first buds appear, back to above the leaf axil. This aids in producing long stems."

How to Harvest Zinnias

Since zinnias thrive when their blooms are trimmed off, they are an ideal addition to your cutting garden. "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," Mbofung-Curtis says.

Schirtzinger recommends cutting zinnias in the evening or in the morning when any overnight moisture has evaporated. "Harvest before the flower completely opens with a firm stem," she says. "Cut stems as long as possible, strip excess foliage, and place in cool water."

Because zinnias are annuals, you don't need to winterize them. Schirtzinger says that saving seeds in the fall can be done with open-pollinated varieties.

Common Problems With Zinnias

Keep zinnias in well-drained, dry areas for best results. "Overwatering and continuous wet conditions can take a great toll since high humidity can lead to the development of powdery mildew, leaf spots, and rot, so water at the base of the plants," Mbofung-Curtis says.

Schirtzinger lists aphids, Japanese beetles, and thrips as common threats to zinnias, and advises watering from the roots instead of from above. "Limiting soil splashing onto the foliage helps decreases foliar disease," she says.