Zinnia flowers are a colorful and long-lasting addition to the flower garden. When you learn how to plant zinnias for your area, you’ll be able to add this popular annual to sunny areas that benefit from their perky blooms.
| Botanical name | Zinnia |
| Family | Asteraceae |
| Origin | Southern North America, South America |
| Life cycle | Annual |
| Plant type | Annual |
| Hardiness zone | 3, 4, 5, 6, 7, 8, 9, 10 |
| Sunlight | Full Sun |
| Maintenance | Low |
| Soil condition | Clay |
| Soil ph | Acid |
| Drainage | Moist but Well-Drained |
| Growth rate | Fast |
| Spacing | Less than 12 in. |
| Flowering period | Fall |
| Height | 8 in. – 4 ft. |
| Width | 8 in. – 4 ft. |
| Flower color | Gold, Yellow |
| Leaf color | Green |
| Stem color | Green |
| Fruit type | Achene |
| Flower benefit | Good Cut |
| Garden style | Butterfly Garden |
| Uses | Coastal |
I. Appearance and Characteristics
Zinnia is a genus of plants of the tribe Heliantheae within the family Asteraceae. They are native to scrub and dry grassland in an area stretching from the Southwestern United States to South America, with a center of diversity in Mexico. Members of the genus are notable for their solitary long-stemmed 12 petal flowers that come in a variety of bright colors. The genus name honors German master botanist Johann Gottfried Zinn (1727–59).
Zinnias are annuals, shrubs, and sub-shrubs native primarily to North America, with a few species in South America. Most species have upright stems but some have a lax habit with spreading stems that mound over the surface of the ground. They typically range in height from 10 to 100 cm tall (4″ to 40″).
The leaves are opposite and usually stalkless (sessile), with a shape ranging from linear to ovate, and a color ranging from pale to medium green. Zinnia’s composite flowers consist of ray florets that surround disk florets, which may be a different color than the ray florets and mature from the periphery inward. The flowers have a range of appearances, from a single row of petals to a dome shape. Zinnias may be white, chartreuse, yellow, orange, red, purple, or lilac.
Zinnias are an annual plant that preferably grows in situ from seed, as they dislike being transplanted. Much like daisies, zinnias prefer to have full sunlight and adequate water. In the preferred conditions they will grow quickly but are sensitive to frost and therefore will die after the first frost of autumn. Zinnias benefit from deadheading to encourage further blooming.
II. How to Grow and Care
Sunlight
Because they come from prairie settings, zinnias prefer full sun. This environment nurtures the best bloom development and helps keep the plants dry.
Temperature and Humidity
Zinnia 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.
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.
Fertilizing
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.
Planting Instructions
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.
Pruning
Deadhead 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.
Propagation
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.
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 Diseases
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.
III. Uses and Benefits
- Ornamental uses
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.
- Companion plants
In the Americas their ability to attract hummingbirds is also seen as useful as a defense against whiteflies, and therefore zinnias are a desirable companion plant, benefiting plants that are intercropped with it. Zinnias are grown in the summertime and bloom all summer long.
- Medicinal uses
Zinnia species are used in folk medicine for the treatment of malaria and stomach pain and are used as hepatoprotective, antiparasitic, antifungal and antibacterial agents. Many studies reported that Zinnia contains numerous secondary metabolites of different classes including sterols, flavonoids, sesquiterpenes, diterpenes and hydrocarbons.
Zinnia plants are also reported to possess a wide range of biological effects such as antioxidant, hepatoprotective, cytotoxic, antibacterial, antifungal and insecticidal activities. This review potentiates the researchers for carrying out further studies on this genus to isolate and develop new drugs from natural sources with wide margin of safety and understanding their effects and possible mechanism of actions.
IV. Harvesting and Storage
Zinnias generally take 60 to 70 days from seed to flower (though it depends on conditions and variety). They work great in a flower bouquet.
To save zinnia seeds for replanting, simply collect a few blossoms that are at least halfway brown and let them dry in a paper bag until the seeds shatter.
- Find the dark, pointed seeds at the bases of outer petals, with more along the center of the flower.
- Dry on a paper towel until hard and almost crisp.
- Store in a paper bag in a dark, dry location until you plant again in the spring.
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