How to Seed a Zinnia
Select a few dried seed heads from your favorite zinnia plant -- if you planted mixed colors , you can even narrow it down to just one color if you like. The seed heads are the centers of the flowers, once the petals have dried and fallen off -- they should be dried and dark brown.
Here is a great link showing different kinds of Zinnia seeds.
If you wish to start your Zinnias indoors, do so 4-6 weeks before the last frost. After the danger of frost has past you can transplant them outside. Zinnias are really easy to grow from seed but they are a little temperamental when transplanted. A school teacher suggested fashioning newspaper into small planters and then when the weather is right planting the seedling (newspaper and all) into the flowerbed. The newspaper biodegrades and the zinnia never has to go through the trauma of a transplant.
Direct Sowing Zinnias
After the last frost date, I recommend direct sowing (tossing directly into the garden) zinnia seeds every two weeks. Seeding every two weeks will allow you to have continuous, fresh blooms and if any of them show signs of disease they can be pulled immediately.
Growing Conditions of Zinnias
Choose a spot with well-drained soil and full sun – these plants need at least six hours of full sun each day. Do not sow the seeds too thickly – zinnias have a high rate of germination, and overcrowding can lead to disease. While the zinnias are growing, water the soil regularly. Once they begin to bloom, regular deadheading will keep your zinnias blooming until the first frost.
Diseases & Pests of Zinnias
Zinnias can be susceptible to gray mold (Botrytis), root rot, powdery mildew, black spot, and leaf blight. Over-watering, crowded plants, dampness, and cool weather can all cause these diseases.
Spotted cucumber beetles (Diabrotica undecimpunctata howardi) like to feast on zinnia petals and flower buds. Both fourlined plant bugs (Poecilicapsus lineatus) and tarnished plant bugs (Lygus lineolaris) are small insects with toxic saliva. Prevent infestation by keeping your garden weed-free in the summer and getting rid of debris in the fall and winter. I found a Wolly Aphid (pictured above) on one of our zinnias and will be sure to post later about its imminent demise.
For a nearly pest-free zinnia, try planting Haage’s zinnia (Zinnia haageana) or narrowleaf zinnia (Zinnia angustifolia), which is also heat-tolerant.
Types of Zinnias:
There are about 20 species of zinnias – they vary in size and can be as small as six inches high and as tall as 36 inches. These are a few of my personal favorites.
Common Zinnia (Zinnia elegans) – one of the most widely grown species of zinnias. Includes the ‘Giant Cactus’ species, a 4-5 inch double-quilled flower that can grow up to 30 inches high.
Narrowleaf Zinnia (Zinnia angustifolia) – disease-resistant species that is also highly heat-tolerant. This species includes the ‘Profusion’ series, which is a 2-inch white, orange, cherry, or coral flower that grows 12-15 inches in height.
Haage’s Zinnia (Zinnia haageana) – smaller cultivar that is disease-resistant.
Zowie Hybrid Zinnia – a striking zinnia with a scarlet center and yellow outer petals. This zinnia hybrid has long-lasting blooms that are 3-5 inches wide.
Benary’s Lime Zinnia (Zinnia elegans) – a premium zinnia in a striking lime-green shade. Produces flowers that have double blooms and measure 4-6 inches across.
Red Spider Zinnia (Zinnia tenuifolia) – medium cultivar (grows 18-24 inches high) with thin, curved petals. Flowers are scarlet with dark centers and just one inch wide.