Jennifer Schultz Nelson
Extension Educator, Horticulture
Zinnias have their own "rags to riches" story in the plant world. Their native range starts in the Southwestern U.S. and stretches to South America. Zinnias are a common wildflower in Mexico, but you probably wouldn't recognize it.
There are about a dozen different species of Zinnia, but one of the most important ancestors of modern cultivars is Zinnia elegans, native to Mexico. In the wild, zinnias are small, weedy, with daisy-like purplish-red flowers. Spanish colonists living in Mexico thought zinnias were ugly, and called them mal de ojos (evil eyes).
As is common practice in the botany world, zinnias got their name from the botanist that first described them, a German named Dr. Johann Gottfried Zinn. The genus name Zinnia is also the common name we use, zinnia. He wrote detailed descriptions of zinnias in the 1700's, but no one really noticed zinnias for almost 100 years after he wrote his descriptions.
European plant breeders were the first to experiment with zinnias and released the first cultivars in the late 1700's. They were an improvement, double-flowered versions of the daisy-like wild zinnia. But zinnias took the flower world by storm in 1920 when Bodger Seeds Ltd. introduced the dahlia-flowered 'Giant Dahlia' and 'California Giant' cultivars. These cultivars are still in production today. In fact I just recently purchased 'California Giant' seeds.
Hidden in the genetics of that weedy looking Mexican wildflower Zinnia elegans was a rainbow of flower color and just about every plant height and flower shape imaginable. There are a few other species commonly available for the garden, but Zinnia elegans dominates the market.
Flower color in zinnias is extensive. You can find any color of the rainbow except for true blue, brown, or black. There are even green-flowered cultivars! Some cultivars have multiple colors on each petal. Last summer I grew 'Zowie Yellow Flame' which was very eye-catching. Each orange-yellow petal was tipped with red, resembling a flame. Another similar cultivar I've grown is 'Swizzle Cherry and Ivory', in which each cherry-red petal is tipped in ivory.
Flower form is another trait that varies widely in zinnia cultivars. Flower size ranges from one-half to two inches. Flowers may be single, semidouble, or double. Single-flowered zinnias have one row of petals, and the center of the flower is visible. Double flowers have many rows of petals, and the center of the flower is hidden. Semidouble flowers are some where in between, with more than one row of petals, but the center of the flower can still be seen.
There are many different flower shapes among the flower forms. Beehive type flowers are double, and their flat petals stack up in such a way that the flowers resemble tiny beehives. Button-type flowers are a flattened version of the beehive. Cactus-flowered types have petals which roll under, twisting and bending, giving the resemblance of a cactus flower. Dahlia-flowered types are large and flat and resemble dahlias.
Plant height is another big variable in the zinnia world. Cultivars range from eight inches to four feet tall. At that rate, you should be able to find a zinnia for every part of your garden!
For success with zinnias, there are a few simple guidelines. First, start with a full sun location in the garden. Sunny locations will produce more flowers, and less disease problems. Well-drained soil is also a must. Fertilize regularly to encourage optimum blooming.
Zinnias are often direct sown into the garden, but you may find limited cultivars available as transplants, or you can grow your own transplants indoors four to six weeks before the last frost. It is not too late to plant zinnia seeds—zinnias are accustomed to warm weather, something in short supply around here this spring. I can attest that the transplants I put out a few weeks ago have not grown a bit in this cool weather, but are just hanging on for dear life! Once it warms up a bit they should take off running.
If you are growing zinnias for cut flowers, some growers plant them closer than usual to encourage longer stems. For other zinnias, make a habit of pinching out the growing tips to encourage bushier, more compact plants. Also, zinnias will flower best with regular deadheading, or removing the spent blooms.
Aphids have few insect pests, the two most common being aphids and spider mites. Both can be controlled with a good insecticidal soap. Aphids can also be blasted off the plant with a strong stream of water from the hose, and spider mites love hot dry conditions, so regular watering will help control them too.
There are a few diseases which affect zinnias, the most common being powdery mildew. If you've grown zinnias, I guarantee you've seen it. Powdery mildew looks like a hazy whitish grey film covering the zinnia leaves. Plants can look absolutely horrible when this disease gets a firm grip. Luckily powdery mildew doesn't typically emerge until late in the growing season.
You can control powdery mildew with applications of fungicide before the disease emerges, or look at improving the plant's growing environment. I highly recommend taking a hard look at the plant's environment before spending money on fungicides. Powdery mildew thrives in cool, wet conditions. Watering at night is a great way to create these conditions, and plants that are too close together will also stay wet longer, promoting this disease. Water only during the day, when plant leaves dry quickly, and space your zinnias out appropriately so that air circulates freely.
Another option is to plant cultivars that have shown resistance to powdery mildew. The species Zinnia angustifolia has shown good resistance to powdery mildew, and there are some award winning cultivars out there such as 'Crystal White', 'Crystal Orange' and the 'Profusion' series which are stars in the garden.
The 'Profusion' series is actually a cross between Zinnia elegans and Zinnia angustifolia. I have grown 'Profusion Cherry' with great success, and this year I'm trying 'Profusion Apricot'. The 'Profusion' series is very compact and spreading, and looks great in borders and beds.
Another great reason to grow zinnias is they attract adult butterflies. Many cultivars produce wide, flat flowers that are perfect landing pads for butterflies needing a nectar refueling break.
You would never know at first glance that the huge diversity within the one hundred plus zinnia cultivars was developed from a wildflower that some people thought was ugly. I guess looks can be deceiving.