Sunflower in Zone 3A — Great Plains

Sunflowers are a fantastic addition to any Great Plains garden. The cheerful blooms brighten up the landscape, plus you get delicious seeds to roast and enjoy. They are also incredibly satisfying to grow, especially in our region with its intense sunshine that helps them thrive.

Our Plains climate can be unpredictable, with extreme temperature swings and the ever-present risk of hail. But with a little planning and attention to timing, you can easily grow sunflowers within our roughly 108-day growing season.

Starting sunflower seeds indoors is an option, but it's generally not necessary since they direct sow so easily. If you want a head start, especially in the northern parts of Zone 3A with the shortest season, you can start seeds indoors from early to late May, about three weeks before you plan to transplant. Use seed trays filled with a good seed-starting mix, keep them warm, and provide plenty of light. Bottom watering helps prevent damping off. Keep in mind that our spring weather can be variable, so watch the forecast closely before transplanting.

Transplant your sunflower seedlings outdoors in early June, once the danger of frost has passed. Before transplanting, harden them off by gradually exposing them to outdoor conditions for about a week. This helps them adjust to the sun and wind. Space them 18-24 inches apart to give them plenty of room to grow. Keep an eye on the weather – a late-season cold snap can still happen, so be prepared to cover your seedlings if necessary.

Direct sowing is the recommended method for growing sunflowers in the Great Plains. Sow seeds late May through early June, when the soil has warmed up. Choose a sunny spot with well-drained soil. Prepare the soil by loosening it and adding compost. Plant the seeds 1-2 inches deep and space them 18-24 inches apart. Sunflowers are easy to direct sow, and with our prairie soil and intense sunshine, they grow quickly.

Sunflowers are moderately drought-tolerant, especially once they've established a deep taproot. However, consistent watering is important, especially during hot, dry periods. In our Plains climate, with its hot summers and variable rainfall, it's crucial to monitor soil moisture.

During the peak of summer, when temperatures soar, water deeply about once a week, providing around 1 inch of water. Use the finger test to check soil moisture: stick your finger into the soil about 2 inches deep. If it feels dry, it's time to water. Water at the base of the plant to avoid wetting the foliage, which can encourage fungal diseases.

In the early part of the season, and as temperatures cool off in late summer, you can reduce watering frequency. Signs of underwatering include wilting leaves, while yellowing leaves can indicate overwatering. A layer of mulch around the base of the plants helps retain moisture and suppress weeds.

You can expect your first sunflower harvest from mid-August through early September, about 80 days after planting. For seeds, wait until the back of the flower head turns brown and the seeds are plump. Cut the entire head off the stalk and hang it upside down in a dry, well-ventilated place to dry completely. For cut flowers, harvest when the petals first open for the longest vase life.

As our first frost approaches in early September, keep an eye on the weather. If frost is predicted, you can cover the flower heads with burlap or blankets to protect them. Any heads that don't fully mature can still be harvested for birdseed.

Here are some common problems you might encounter growing sunflowers in the Great Plains:

Birds Eating Seeds

• What it looks like: Seed heads are stripped bare, with missing or damaged seeds.
• What causes it: Birds love sunflower seeds! They're a readily available food source, especially during migration.
• How to fix/prevent it: Cover the seed heads with netting or paper bags once the petals start to dry. You can also try planting extra sunflowers to share with the birds.

Sunflower Moth

• What it looks like: Small caterpillars burrowing into the seed head, leaving behind webbing and frass (caterpillar poop).
• What causes it: Sunflower moths lay their eggs on the flower heads, and the larvae hatch and feed on the developing seeds.
• How to fix/prevent it: Inspect flower heads regularly for signs of infestation. Remove and destroy any infested heads. Encourage beneficial insects like parasitic wasps that prey on sunflower moth larvae.

Downy Mildew

• What it looks like: Yellow patches on leaf tops with fuzzy gray-purple growth on undersides. Leaves brown and die from the bottom up.
• What causes it: An oomycete pathogen that spreads in cool, humid conditions via wind-carried spores.
• How to fix/prevent it: Remove affected leaves immediately. Improve air circulation. Water at the base, never overhead. Copper-based fungicides can be used for prevention. Plant resistant varieties where available.

Great Plains Specific Challenges: Our hot, dry summers and variable rainfall can stress sunflowers, making them more susceptible to pests and diseases. Wind protection is essential to prevent plants from toppling over, especially the taller varieties. Hail can also damage leaves and flower heads, so consider providing some form of protection if severe weather is predicted.

Sunflowers have some great companion plants that can help them thrive in our Plains gardens. Cucumbers and squash benefit from the shade provided by sunflowers, which helps retain soil moisture. Green beans fix nitrogen in the soil, which helps sunflowers grow. Corn provides wind protection for sunflowers, while lettuce benefits from the partial shade. Avoid planting potatoes near sunflowers, as they compete for the same nutrients in the soil.