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Missouri Environment & Garden


David Trinklein
University of Missouri
Plant Science & Technology
(573) 882-9631

Zinnia: Not the Flower Grandma Grew

David Trinklein
University of Missouri
(573) 882-9631

Published: July 10, 2017

multi-colored zinnia

In the search for a durable, colorful annual flower able to handle the rigors of a typical Missouri summer, zinnia ranks high on the list of possibilities. Available in nearly every color of the rainbow, its heat and drought tolerance along with its low-maintenance nature make it a familiar sight in annual beds and borders.

For decades, zinnia's major detraction had been its susceptibility to powdery mildew. Fortunately, plant breeders have made great strides in improving zinnia's ability to tolerate the troublesome disease while improving its desirable qualities. If you haven't grown zinnias recently, you are in for a pleasant surprise. In short, today's zinnia is not the flower grandma used to grow.

The common garden zinnia (Zinnia elegans) is a member of the sunflower (Asteraceae) family of plants and a native of Mexico. Evidently, the Spanish explorers who first encountered zinina were not terribly impressed and named it mal de ojos which, literally interpreted, means "sickness of the eye". Fortunately, not everyone shared their opinion of the flower. Thanks to the work of European plant breeders who began selecting zinnias for their desirable characteristics, zinnia was introduced into the gardening world in the 19th century. It is named in honor of Johann Gottfried Zinn, an 18th century botanist and anatomist.

As a garden flower, zinnia first became widely popular in the United States around 1920 when Bodger Seed Company introduced a variety named 'Giant Dahlia'. The name refers to the fact that zinnias come in two flower forms: dahlia and cactus. Dahlia-flowered zinnias have ray florets (petals) that are broad, tightly-packed and extend somewhat downward that their tip. Cactus-flowered zinnias have quill-like petals whose edges are reflexed downward.

Thanks to plant breeding, zinnias are available in every size and color imaginable. It's a bit hard to imagine that towering giants such as 'State Fair Mix' which easily achieves a high of three feet and bears flowers six inches in diameter belong to the same species as diminutive varieties such as 'Thumbelina'. The latter rarely exceeds six inches in height and bears flowers about an inch and one-half in diameter.

Zinnias are great garden flowers 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 difficult to grow. It is one of the few garden flowers that can be started equally well by planting seeds directly in the garden or by purchasing 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. Space according to variety. 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 is by far the most frequently encountered disease, however plant breeders have made progress in combating this disease. Several of the newer cultivars (e.g. the 'Magellan®' series) appear to be more tolerant of mildew than are the older ones. In all cases, keeping foliage as dry as possible (do not overhead irrigate) and spacing plants apart for good air circulation can help manage the disease. Fungicides labeled for powdery mildew control also can be used as a preventative measure.

For those wishing to re-acquaint themselves with this willing visitor to Missouri gardens, there are many new varieties to try. The afore-mentioned 'Magellan®' series comes highly recommended. It boasts vigorous and uniform plants that mature to a height of 12 to 14 inches. Its large, fully-double flowers are vibrant in color and of exceptional quality.

Additional newcomers to the zinnia world include the 'Profusion®' series (Zinnia x hybrida) and the 'Zahara®' series (Zinnia marylandica). Both bear abundant flowers two to three inches in diameter are available in a variety of colors. Plants are 12-18 inches in height and extremely disease resistant. Although not terribly effective as cut flowers because of their small size, these two series of zinnia provide a virtual riot of color in the garden with minimal care. Both series feature All American Selection (AAS) winners. The latter includes 'Profusion®' orange, white, red, double hot cherry and double deep salmon, as well as 'Zahara®' starlite rose, double fire and double cherry.

Another relatively new zinnia that deserves trying is 'Crystal White'. It, too, is an AAS winner that is a member of the species known as lance-leaf zinnia (Zinnia angustifolia). It has a dwarf, spreading habit and is literally covered with two-inch diameter flowers all summer, making it an ideal choice for edging. Its disease resistance is excellent as is its ability to tolerate heat. Other new and exciting varieties of zinnia exist. When in doubt about which ones to try, look for those that are AAS winners.

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, sizes and types as zinnia. If you have not tried this fan of Missouri's hot, humid summers lately, you are in for a pleasant surprise.

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REVISED: February 21, 2017