Why Not Zinnias?

When questioned about planting zinnias, a seasoned gardener once remarked, "There are two types of zinnias: those that have mildew and those that will get mildew." Unless one has grown zinnias recently, one is in for a pleasant surprise because plant breeders have made remarkable progress in improving this garden standard. In short, it’s not the same zinnia that grandma used to grow.

The common garden zinnia (Zinnia elegans) is a native of Mexico. Evidently, the Spanish explorers who first encountered this plant were not terribly impressed and named it "al de ojos," which literally interpreted means "sickness of the eye." Fortunately, not everyone shared this opinion, and zinnia was introduced into the gardening world. It is named in honor of Johann Gottfried Zinn, an 18th century professor of botany. The zinnia first became widely popular in the United States around 1920 when Bodger Seed Company introduced a cultivar named ‘Giant Dahlia’. Thanks to plant breeding, today’s zinnias are available in several flower forms and in every size and color imaginable. It’s a bit hard to imagine that towering giants such as ‘State Fair Mix’ and the diminutive ‘Thumbelina’ belong to the same species.

Zinnia is a great garden flower for Missouri for several reasons. First, they adore heat--which is a real plus for a garden plant in the "Show-Me State" during the months of July and August. Second, they are very versatile in the garden, serving equally well in beds or borders, depending upon the cultivar chosen. Additionally, the taller, large-flowered cultivars make excellent, long-lived cut flowers for those interested in enhancing their interior decor. Finally, they are "user-friendly" and not terribly difficult to grow. It is one of the few garden plants that can be started with equal success by planting seeds directly in the garden or by purchasing started transplants. If direct seeding is done, one should wait until the soil has warmed, which, in Missouri, means the month of May.

Zinnias prefer a well-drained garden loam of moderate fertility. Vigorous by nature, they are, however, prone to attack by several pests. Spider mites, along with chewing insects such as grasshopper and "bud worms," can be troublesome. Powdery mildew, however, is by far the most frequently encountered disease here where plant breeding has made progress. Several of the newer cultivars are more tolerant of the disease than are the older ones. In all cases, keeping foliage as dry as possible (don’t overhead irrigate) and spacing plants apart for good air circulation can help in managing the disease. A fungicide can be used as a preventative measure.

For those wishing to re-acquaint themselves with this willing visitor to our gardens in Missouri, there are many new cultivars to try. Of particular interest is the ‘Profusion’ series, which comes highly recommended. This series, which includes cherry, orange, and white, represents an inter-specific hybrid of zinnia and features plants 12-18 inches in height topped with flowers 2-3 inches in diameter. Abundance of bloom is excellent; freedom from disease is significant, especially with regard to mildew. Although not terribly effective as cut flowers because of their size, they do provide a virtual riot of color with minimal care in the garden. Several colors of the Profusion series were individual All-American selections.

Another new zinnia worth trying is ‘Crystal White’. This recent All-American selection is actually a separate species known as lance-leaf zinnia (Z. angustifolia).

It has a dwarf spreading habit and is literally covered with 2-inch diameter flowers all summer, making it an ideal choice for edging. Its disease resistance is excellent as is its tolerance of heat. Other new and exciting cultivars of zinnia exist, although their disease resistance is not as great as those mentioned above.

When all is said and done, few garden plants are as easily grown, enjoyed as much, or come in such a wide diversity of colors and types as does the zinnia. If you have not tried this fan of Missouri’s hot, humid summers lately, you are in for a pleasant surprise.

David Trinklein, Professor of Horticulture, UMC (573) 882-9631