Zinnias - A Burst of Hot Flower Colors from Zinnias

Double Zinnia Flower
Photo: © Marie Iannotti

Overview and Description:

Zinnias are a gift from Mexico but gardeners everywhere can easily grow them. They are warm season annual flowers that bloom with abandon and require only minimal care. It doesn't matter how hot the summer gets, zinnia plants just keep on blooming. Although some varieties can be plagued with powdery mildew problems, there are plenty of new zinnias that can even handle humidity.

Although we traditionally think of zinnias as bold, hot-palette colors, there are new ones being introduced every year, including some cooling whites.There are tall, short, and spreading varieties and they all are very easy to grow, withstanding some of the worst growing conditions.

  • Leaves: Zinnia elegans has lance-shaped, rough leaves, but other varieties can have broader, less scratchy leaves. It's the foliage that gets powdery mildew.
  • Flowers: Wide variety of bold colored, rounded flowers. There are dwarf varieties and tall varieties that will grow up to 4 ft. tall. Flowers can be daisy-like, double, cactus-flowered or a formal looking dahlia like flower. Color range includes saturated shades of: white, yellow, orange, red and purple.

Botanical Name:

Zinnia sp. and hybrids

Common Name(s):

Zinnia

Hardiness Zone:

Zinnias are one of the few plants that are true annuals. Many plants labeled as annuals are actually perennials that are only hardy in the warmest hardiness zones, but zinnias will be annuals everywhere.

Mature Size:

There are spreading and dwarf zinnias that only grow about 6 - 8 in. tall and the classic Zinnia elegans can reach 4 ft. tall.

Exposure:

You really want to plant zinnias in a spot with full sun. You will get the most prolific blooms in a sunny spot and it will help to keep the leaves dry and thwart powdery mildew before it starts.

Bloom Period/Days to Harvest:

Zinnia plants can take a few weeks to become established by once it warms up, expect them to bloom from summer right through fall.

Design Tips:

The vibrant, tropical colors of zinnias work well in a hot border, picking up the hues of other reds and oranges. They are also nice for adding dramatic color to a container.

The tall Zinnia elegans is still a favorite for the back of the border, but new varieties, like the Thumbelina series, grow only about 6 in. tall and make great choices as edging or in containers.

Zinnia angustifolia has a low, spreading habit that, combined with zinnias ability to withstand heat and lousy soil, is perfect for along the walkway. The Crystal series is amazingly drought and abuse tolerant.

The Profusion series solved the problem of zinnia's for mildew. As wonderful as the Profusion zinnias are, the Zahara™ zinnias are causing even more of a stir with their new maintenance free habit; no mildew, no deadheading, no problem.

Suggested Varieties:

  • Zahara™ Series - Very mildew resistant, with larger flowers than the Profusion series. (12 - 18 in. tall)
  • Zinnia elegans ‘Dreamland Series’ - Double flowerheads on a compact dwarf plant. Lots of colors (8-12 in. tall)
  • Zinnia elegans ‘Envy’ - semi-double chartreuse flowers that light up the shade. (30 in. tall)
  • Zinnia haageana ‘Orange Star’ - A bushy dwarf variety with orange flowers that is very mildew resistant. (6 in.tall)

Growing Tips:

Soil: The only real soil requirement is that it be well-draining. Zinnias do not like to sit in damp soil and I've already harped on their penchant for mildew. It helps to have a soil pH in the neutral range, but it's not mandatory.

Planting: Zinnia is extremely easy to start from seed. You can direct sow as soon as the soil has warmed a bit and there's no chance of frost. You could also start seed indoors, about 4 - 6 weeks before your last frost date. And every garden center has zinnia seedlings for sale, however you'll have less choice of varieties.

Zinnias are hot weather lovers and will sit and wait for the temperature to warm up before really starting to grow.

Maintenance: Zinnias are very drought tolerant and don't usually need any supplemental watering. If your soil is poor, you can add some compost to give the plants a boost, but they will grow in even bad soil. However they probably won't thrive without either some organic matter in the soil or a bit of fertilizer every month.

You can deadhead for longer bloom, but it's not absolutely necessary. They may pause flowering for awhile, but they'll start up again.

As mentioned, some varieties can be very prone to powdery mildew. You can try and counter that with the milk cure, but check frequently and consider removing any affected plants.