Sunflower in Zone 6B — Great Plains

Sunflowers just shout summer, and they're a rewarding crop for Plains gardeners. Whether you're after a cheerful backdrop, tasty seeds, or cut flowers, they're surprisingly versatile. Plus, they handle our prairie soil and intense sunshine like champs.

We all know the Plains throws curveballs—wind, hail, and those extreme temperature swings. But with sunflowers, the timing is on our side. Our 198-day growing season gives you plenty of wiggle room to get a good harvest.

Starting sunflower seeds indoors isn't usually necessary, given how easily they direct-sow. But if you're itching to get a head start, or if you're trying to squeeze in a late-season crop, it's doable. Start seeds indoors mid-March through early April, about 3 weeks before you plan to transplant.

Use seed trays with a good seed-starting mix. Keep them warm and provide plenty of light—a sunny south-facing window or grow lights work well. Bottom watering helps prevent damping-off; just set the tray in a shallow dish of water until the soil surface is moist. Remember, our springs can be variable, so keep an eye on the forecast before transplanting.

Transplant your sunflower seedlings outdoors mid-April through mid-May, after the risk of hard frost has passed. Before planting, harden them off by gradually exposing them to outdoor conditions for about a week. Start with an hour or two of shade, increasing the time and sun exposure each day.

Space them 18-24 inches apart. Keep an eye on the wind. Those young plants can be fragile, and a sudden gust can snap them. If a late cold snap threatens, be ready to cover them.

Direct sowing is the way to go with sunflowers here on the Plains. It's simple and reliable. Sow seeds early April through late July for a continuous harvest.

Choose a spot with full sun and well-drained soil. Sunflowers aren't too picky, but they'll thrive in soil amended with compost. Make sure the soil temperature is at least 60°F. Plant seeds about 1 inch deep and space them 18-24 inches apart. Keep the soil consistently moist until seedlings emerge.

Sunflowers are surprisingly drought-tolerant once they get established, thanks to their deep taproot. But that doesn't mean you can neglect them, especially during our hot Plains summers. The key is to water deeply but infrequently.

During the spring, when rainfall is more frequent, you might only need to supplement with water every week or two. Once the summer heat kicks in, increase watering to once a week, or even twice if we're in a dry spell. Stick your finger about 2 inches into the soil near the base of the plant. If it feels dry, it's time to water. Aim for about 1-2 inches of water per week, either from rain or irrigation. Water at the base of the plant to avoid wetting the foliage, which can encourage disease in our low-to-moderate humidity.

Wilting leaves are a sign of underwatering, while yellowing leaves can indicate overwatering. A good layer of mulch around the base of the plants helps retain moisture and suppress weeds, which is especially helpful in our variable climate.

Expect your first sunflower harvest late June through late October, about 80 days after planting. The timing depends on when you sowed your seeds and the specific variety.

For sunflower seeds, wait until the back of the flower head turns brown and the seeds are plump and slightly loose. You can protect the heads from birds with netting. For cut flowers, harvest when the petals first open. Cut the stem at an angle and place it in water immediately. As frost approaches in late October, harvest any remaining heads, even if they're not fully mature. You can hang them upside down in a dry, well-ventilated place to finish ripening.

Here are the top 3 problems you might face with sunflowers in our region:

Birds Eating Seeds

• What it looks like: Missing seeds, pecked-at flower heads, general bird mayhem around your sunflowers.
• What causes it: Birds love sunflower seeds, plain and simple. Our open Plains environment offers few natural barriers.
• How to fix/prevent it: Netting is your best bet. Cover the flower heads with netting as they mature. Reflective tape can also deter birds.

Sunflower Moth

• What it looks like: Webbing, frass (insect poop), and damaged seeds within the flower head.
• What causes it: Sunflower moths lay their eggs on the developing flower heads. The larvae then burrow in and feed on the seeds.
• How to fix/prevent it: Monitor your plants regularly. Bacillus thuringiensis (Bt) is an effective organic control if applied early. Remove and destroy infested heads.

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 help prevent it. Plant resistant varieties where available.

Great Plains Specific Challenges: Our hot summers can stress sunflowers, making them more susceptible to pests and diseases. The wind can also be a problem, especially for tall varieties. Staking can help prevent them from toppling over. Variable rainfall means you need to be vigilant about watering, especially during dry spells.

Sunflowers play well with several garden buddies in the Plains. Cucumbers and squash benefit from the sunflower's shade during our intense summers. Green beans can use the sunflower stalks as a trellis. Corn and sunflowers are classic companions, with the corn providing wind protection for the sunflowers. Lettuce appreciates the partial shade offered by sunflowers, especially during the hottest part of the day. Avoid planting potatoes near sunflowers. Potatoes and sunflowers compete for the same nutrients in the soil, which can stunt the growth of both plants.