Green Thumb – Zinnias

Posted: August 18, 2022

I’m sentimental about zinnias. They are the first flowers I ever grew as a child. My dad dug up a small plot on the south side of our house and showed me how to plant the seeds. I watered them with a sprinkling can. They sprouted fast, grew tall, and bloomed big. I felt joy and pride.

Zinnias are easy annuals to grow, and once they get going they will reward you with flowers right up until frost. They make nice cut flowers, butterflies love many of them, and they are deer-resistant.

There are many unique varieties, but the three main types are single-flowered, double-flowered and semidouble-flowered. The flowers also come in interesting shapes. There are smaller zinnias to edge a border or grow in a container. The tall ones look good at the back of a flowerbed.

Zinnias need lots of sun. They grow in many types of soil, but always do best in well-drained soil that has been supplemented with compost. They love hot weather.

Sow the seeds directly into the garden. The seeds are large and easy to handle. Zinnias don’t like to be transplanted, so if you start them indoors, transplant them carefully when the plants are small.

Plant the seeds about ¼ inch deep, after the last frost, when the minimum daytime temperature is at least 60 degrees. They will start to sprout in as little as four days, though generally it take 60-70 days to flower.

Photo courtesy of Janice Weber

When the seedlings are about three inches tall, thin them to 6 to 18 inches, depending on their final size.

This will give them good air circulation to prevent powdery mildew in late summer. Water early in the day so the leaves have time to dry out.

Keep the soil moderately moist and fertilize them lightly for the most flowers. Otherwise they are pretty much maintenance-free and also drought tolerant. If you cut off the old flowers you will encourage more to form.

Zinnias are good cut flowers which can last a week or more in a vase. The sturdy stems of the taller varieties can work well in a floral arrangement.

If you are interested in attracting butterflies and other pollinators look for single flower varieties. When they are grown in a vegetable garden they can attract pollinators that control pests. Many zinnia varieties have double flowers. Though they are not the best food source for pollinators, they have one important feature. They remain open longer because they don’t focus on seed production.

Here are some recommended zinnia varieties to look for:

  1. The Thumbelina Series are dwarf, growing 6 inch stems with petals 11/4 inch across. They have single or semi-double flowers.
  2. The Dreamland Series are dwarf and compact with double flowerheads. Stems are 8-12 inches tall and produce flowers up to 4 inches across.
  3. The State Fair Series are one of the tallest. The double flowerheads are 3 inches across on 30 inch tall stems.
    The zinnia is named after botanist, Johann Gottfried Zinn. The flower was brought to Europe from Mexico in 1753. In January 2016 NASA released images of a zinnia flower blooming aboard the International Space Station. It was the first flower grown in space from start to finish.

Janice M. Weber – University of Illinois Extension, DeKalb County Master Gardener

DeKalb County Master Gardener Help Desk

Do you have yard and garden problems or questions? Master Gardeners research topics about insects, trees, shrubs, plants, vegetables, fruits, gardens, lawns, and more. Call the University of Illinois Extension Horticulture Help Desk at 815-758-8194 or email uiemg-dekalb@illinois.edu. The Desk is open for questions from 10 a.m. – Noon, Monday, Wednesday and Friday.


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