How to Plant and Grow Zinnia

Zinnias come in many shapes, sizes, and colors (excluding blue) and are some of the toughest annuals you can plant. Zinnias are a favorite with pollinators such as hummingbirds, bees, and butterflies that land on the flowers and drink their nectar. Tall varieties are an excellent choice for cut flowers, with options that include cactus and quill-type blooms with long, narrow petals and pompom-type blooms that look like little spheres. Since zinnias come in a variety of colors, they work well in almost any flower arrangement.

While tall zinnias suit cottage and cutting gardens, their lower-growing, mounding or spreading varieties work well in containers. They also require less frequent deadheading than their taller counterparts.

Where to Plant Zinnia

Plant zinnias in an area where they will receive full sun. They can flower in partial shade, but they’ll produce fewer flowers and be more susceptible to disease. They grow equally well in a garden bed or a container, but the soil must be well-draining. If it isn’t, they are susceptible to root rot.

Tall zinnia varieties are perfect for the back of a garden border or a cutting garden. Their strong, long stems make them excellent candidates for cut flower arrangements. Gardeners often grow clumps of several plants together for a stunning effect. Shorter varieties have more of a mounding appearance and are attractive front-of-the-border options.

How and When to Plant Zinnia

Zinnias are warm-weather annuals that don’t like cold weather or cold soil, so they shouldn’t be set out or sown outdoors before the soil warms in spring.

For an early start, sow seeds indoors in pots filled with moist seed-starting mix four to six weeks before the last spring frost date. Cover them with 1/4 inch of soil (they need darkness to germinate) and put them in a sunny window until they are ready to transplant. They germinate in 7-10 days and should be at least 4 inches tall before being transplanted outside. When working with zinnias, never handle them by the stems—only by the rootballs.

When direct sowing outside in warm weather, cover the seeds with 1/4 inch of soil. The seeds germinate in 7-10 days. When they are 2 inches tall, thin them to 8-24 inches apart, depending on the variety.

Zinnia Care Tips

Light

Because they come from prairie settings, zinnias prefer full sun. This environment nurtures the best bloom development and helps keep the plants dry.

Soil and Water

Native to grassland areas, established zinnias are tough plants that handle drought well. However, young plants need to grow in moist soil, so water deeply a couple of times a week. Don’t overwater. Zinnias don’t handle wet roots well.

Even though they grow best in well-drained soil high in organic matter, zinnias are tolerant of poor soils, including hard clay. Amend poor soil before planting for the best flower production.

Temperature and Humidity

Zinna seeds germinate between 70°F and 75°F. After germination, their preferred daily temperature is 75°F-85°F, although 65°F at night is acceptable. They aren’t fond of high humidity but will tolerate it.

Fertilizer

No matter where your zinnias grow (garden on container), they will benefit from a side dressing of 5-5-5 fertilizer when the flowers start to form. During the growing season, the occasional liquid fertilizer application helps them bloom all season long. Fertilizer is especially important in containers filled with a soilless potting medium. In all cases, follow the product instructions for the proper quantity.

Pruning

Deadhead spent blooms regularly to keep the plant tidy and encourage additional blooms. To encourage branching and more flowers in tall varieties, pinch the growing tip from young plants. However, pinched plants will be shorter and may bloom later. No additional pruning is needed as these plants are annuals that must be replanted each year.

Potting and Repotting

The shorter varieties of bedding zinnias are excellent container plants. Avoid the tallest zinnias for this purpose. Use a container that is at least 12 inches wide and 12 inches deep and fill it with well-draining garden soil enriched with compost. Sow a few seeds outside in a container immediately after the weather warms—thinning as needed later—or start seeds early indoors in a container and move it outside at the right time.

Pests and Problems

One problem with zinnias is root rot, which is prevented by planting in full sun and not overwatering the plants. Japanese beetles love zinnias, and gardeners have turned to beetle traps for years with mixed results. If you have only a few, handpick them off.

Unless they are planted in full sun, zinnias may be afflicted by powdery mildew—a condition most commonly seen as a white powder on the plant’s bottom leaves. While this pesky fungus probably won’t kill the plants, it does diminish their beauty. The best control method for powdery mildew is prevention; look for resistant zinnia varieties and keep plenty of airflow space around the plants.

Leaf spot and blight are two other common diseases found in zinnias. Similar to powdery mildew, these conditions are caused by fungi. Control methods are the same: Remove any debris from the base of the plants to keep them clean.

How to Propagate Zinnia

Saving zinnia seeds is an excellent way to start next year’s plants. Zinnia seeds are often sold as mixes, so you don’t have to worry about seedlings being identical to the parent plant. As old flower heads dry, remove the spent blooms and harvest the small arrowhead-shaped seeds from each petal by shaking the dried flower heads in a paper bag. Store the seeds in a dry, warm area until the weather warms in spring.

Zinnias can also be propagated in water with cuttings in about 3-4 weeks. In spring, cut 4-6 inches from the tips of stems and remove the leaves from the bottom half of the cuttings. Put the cuttings in a glass or jar with enough water to cover the bottom half of the cuttings, making sure some leaf nodes are underwater. Place the container in a warm area with bright light but not full sun. When a root structure develops and the weather warms, transplant the zinnias to the garden.

Types of Zinnia

‘Benary’s Giant Orange’ Zinnia

Zinnia elegans ‘Benary’s Giant Orange’ is an excellent cut flower with large, 4-inch-wide, double orange blooms. It grows 38 inches tall and 2 feet wide.

‘Magellan Mix’ Zinnia

Zinnia elegans ‘Magellan Mix’ has double blooms in a wide range of shades, including red, pink, yellow, orange, and white. It grows 16 inches tall.

‘Parasol Mix’ Zinnia

Zinnia elegans ‘Parasol Mix’ bears fully double, petal-filled flowers in various shades. It grows 12 inches tall.

‘Cut and Come Again’ Zinnia

Zinnia elegans ‘Cut and Come Again’ is especially free flowering and bears double flowers in a range of bright colors on a 4-foot-tall plant.

‘Profusion White’ Zinnia

Zinnia elegans ‘Profusion White’ is an early-flowering selection with good disease resistance and white flowers all summer. It grows 18 inches tall and 10 inches wide.

‘Scarlet Flame’ Zinnia

Zinnia elegans ‘Scarlet Flame’ offers double red flowers on a vigorous, 42-inch-tall plant.

‘Zahara Coral Rose’ Zinnia

Zinnia marylandica ‘Zahara Coral Rose’ bears big flowers in a soft shade of pink. It’s a disease-resistant, heat-loving plant that grows 18 inches tall and wide.

‘Zahara Starlight Rose’ Zinnia

Zinnia marylandica ‘Zahara Starlight Rose’ is a compact (to 18 inches tall and wide), award-winning selection with white flowers that have a distinct pink blush. It’s very disease-resistant.

‘Zahara White’ Zinnia

Zinnia marylandica ‘Zahara White’ is a compact selection that grows to 18 inches tall and wide with big white flowers. It’s a disease-resistant, heat-loving variety.

‘Zahara Yellow’ Zinnia

Zinnia marylandica ‘Zahara Yellow’ produces big flowers in a bright, bold color on a disease-resistant, heat-loving plant that grows 18 inches tall and wide.

Zinnia Companion Plants

Spider Flower

It’s amazing that the tall, dramatic spider flower is only an annual. Once temperatures warm up, it zooms to 4 feet or more, buds very quickly, and produces large balls of flowers with fascinating long seedpods that whirl out from it. Cut it for vases, but be aware that the flowers shatter easily after a few days. It typically self-seeds prolifically, so you only have to plant it once. Because it develops surprisingly large thorns, it’s best to keep spider flower away from walkways. Plant seedlings in spring after all danger of frost has passed. Cleome does best in moderately rich, well-drained soil. Be careful about fertilizing, or you’ll have extremely tall floppy plants. Group in clusters of six or more for best effect.

French Marigold

Just as you’d expect from something called French, these marigolds are the fancy ones. French marigolds tend to be frilly, and some boast a distinctive “crested eye.” They grow roughly 8-12 inches high with a chic, neat, little growth habit and elegant dark green foliage. They do best in full sun with moist, well-drained soil and will flower all summer long. They may reseed, returning year after year in spots where they’re happy.

Salvia

Many gardens have at least one salvia growing in them. Whether you have sun or shade, a dry garden or lots of rainfall, there’s an annual salvia that you’ll find indispensable. All attract hummingbirds, especially the red ones, and are great picks for hot, dry sites where you want tons of color all season. Most salvias don’t like cool weather, so plant them outdoors after all danger of frost has passed.