Zinnia in Zone 5A — Great Plains

Zinnias are a must-grow in the Great Plains. Their bright, cheerful blooms bring vibrant color to our gardens, attracting pollinators and adding beauty to bouquets. Plus, they're relatively easy to grow, offering a high reward for your effort, even in our sometimes challenging climate.

We Plains gardeners know all about extreme weather, from spring temperature swings to summer heat and the ever-present hail risk. But don't worry, with a little planning around our 168-day growing season, you can enjoy a riot of zinnia color from mid-summer right up until the first frost.

Starting zinnias indoors gives you a head start, but honestly, it's often not necessary here on the Plains. Our prairie soil warms up quickly, and zinnias germinate readily when direct sown. However, if you're aiming for extra-early blooms or live in the northern part of our region with a shorter season, it's a viable option.

If you choose to start indoors, sow seeds early to late April, about four weeks before you plan to transplant. Use seed trays with good drainage and keep them in a warm spot with plenty of light – a sunny windowsill or under grow lights. Water from the bottom to prevent damping off. Just set the tray in a shallow container of water until the soil surface is moist. Keep in mind our spring weather can be variable, so be ready to protect seedlings from late cold snaps.

Transplant your zinnia seedlings outdoors early May through early June, once the danger of frost has passed. Before transplanting, harden off your seedlings by gradually exposing them to outdoor conditions for about a week. Start with an hour or two of shade and increase the time each day.

When transplanting, space zinnias 6-12 inches apart, depending on the variety. Choose a sunny spot with well-drained soil. Keep an eye on the forecast – a late hailstorm can decimate young transplants, so be prepared to cover them if needed.

Direct sowing is the easiest way to grow zinnias in the Great Plains. Wait until the soil has warmed up, typically early May through late July. Zinnias germinate best when soil temperatures are consistently above 60°F.

Prepare the soil by loosening it and removing any weeds or debris. Sow seeds about ¼ inch deep and space them 6-12 inches apart. Keep the soil consistently moist until the seedlings emerge. Direct sowing is a great option, but keep in mind that young seedlings are vulnerable to pests and weather extremes, so monitor them closely.

Zinnias need moderate watering, especially when they're young. Once established, they can tolerate drier conditions, but consistent moisture encourages more blooms. The key is to water deeply but infrequently.

During the hot Plains summers, check the soil moisture regularly. Stick your finger about 2 inches deep – if it feels dry, it's time to water. Aim for about 1 inch of water per week, but adjust based on rainfall and temperature. Water at the base of the plants to avoid wetting the foliage, as wet leaves can lead to powdery mildew in our low-to-moderate humidity.

Signs of underwatering include wilting leaves and stunted growth. Overwatering, on the other hand, can cause yellowing leaves and root rot. Mulching around the base of the plants helps retain moisture and suppress weeds, which is especially helpful during our variable rainfall patterns.

Deadheading is essential for keeping your zinnias blooming throughout the season. Simply pinch or cut off the spent flowers just below the flower head. This encourages the plant to produce more blooms instead of putting energy into seed production.

You can deadhead zinnias anytime you see a faded flower. Don't be afraid to cut long stems for bouquets! The more you cut, the more flowers you'll get. As the first frost approaches in early October, you can cut all the remaining flowers to enjoy indoors.

You can expect your first zinnia harvest starting early July and continuing through early October. Zinnias are ready to cut when the flowers are fully open and the stems are strong. The more you cut, the more the plant will produce.

To harvest, cut the stems at an angle, preferably in the morning. Remove any leaves that will be below the water line in your vase. Zinnias are excellent cut flowers and have a long vase life. As the end of the season approaches and you know a hard frost is coming, cut all the remaining blooms to enjoy indoors.

Zinnias are generally easy to grow, but they can be susceptible to a few problems in the Great Plains. Here's how to identify and address them:

Powdery Mildew

• What it looks like: White or grayish powdery coating on leaves, stems. Leaves curl, yellow, and die, reducing plant vigor.
• What causes it: Various fungi that thrive in warm days, cool nights, and moderate humidity. Dry leaf surfaces actually favor it (unlike most fungi).
• How to fix/prevent it: Improve air circulation through spacing and pruning. Remove affected leaves. Neem oil or potassium bicarbonate sprays can help. Milk spray (1 part milk to 9 parts water) is surprisingly effective. Plant resistant varieties.

Bacterial Leaf Spot

• What it looks like: Small, water-soaked spots on leaves that enlarge and turn brown or black. Spots may have a yellow halo.
• What causes it: Bacteria spread by splashing water, especially during periods of high humidity or rainfall.
• How to fix/prevent it: Avoid overhead watering. Improve air circulation. Remove and destroy infected leaves. Copper-based fungicides can help prevent further spread.

Alternaria Blight

• What it looks like: Dark brown or black spots on leaves, often starting on lower leaves. Spots may have concentric rings.
• What causes it: Fungus that thrives in warm, humid conditions. Spreads by wind and splashing water.
• How to fix/prevent it: Remove and destroy infected leaves. Improve air circulation. Fungicides containing chlorothalonil or copper can help.

Great Plains Specific Challenges: Our hot, dry summers can stress zinnias, making them more susceptible to disease. Be sure to water deeply and regularly, especially during periods of drought. The strong winds we often experience can also damage plants, so consider providing some wind protection, especially for taller varieties.

Companion planting can help your zinnias thrive. Plant zinnias near tomatoes and peppers, as they attract beneficial insects that prey on pests that bother those crops. Squash and cucumbers also benefit from zinnia's pollinator-attracting abilities, leading to better fruit set. Avoid planting zinnias near plants that are susceptible to powdery mildew, as this can increase the risk of spreading the disease.