Sunflower in Zone 6A — Mountain West

Sunflowers are a fantastic addition to any Mountain West garden. Their bright, cheerful faces bring joy, and the seeds are delicious roasted or used for birdseed. Plus, the height of the plants adds visual interest and can even provide some afternoon shade for more delicate plants.

Our high altitude and intense sun here can be a bit of a challenge for some plants, but sunflowers thrive in these conditions. With a little attention to timing and watering, you can easily grow sunflowers in our short, 153-day growing season.

While sunflowers prefer direct sowing, you *can* start them indoors if you're eager to get a head start. Start your seeds indoors from early April through early May, giving them about 3 weeks before the last expected frost. Use seed trays with a good seed-starting mix, and provide warmth and plenty of light.

Bottom watering is especially helpful for seedlings, as it prevents damping off. Remember that spring here in the Mountain West often has temperature swings, so keep an eye on your seedlings and adjust their environment as needed.

If you started your sunflower seeds indoors, you can transplant them outdoors from early May through early June, after the risk of frost has passed. Before transplanting, harden off your seedlings by gradually exposing them to outdoor conditions for about a week. This will help them adjust to the intense sun and cooler nights we often experience.

When transplanting, space your sunflower plants 18-24 inches apart. Be mindful of potential late-season cold snaps, and be prepared to cover your young plants if necessary.

Direct sowing is the preferred and easiest method for growing sunflowers in our region. Sow your seeds directly into the garden from early May through late June. Ensure the soil has warmed up to at least 60°F (15°C) for optimal germination.

Prepare your planting area by loosening the soil and amending it with compost if needed. Plant seeds about 1 inch deep and space them 18-24 inches apart. Sunflowers are easy to direct sow and grow quickly, so you'll see sprouts in no time.

Sunflowers are moderately drought-tolerant once they're established, thanks to their deep taproots. However, consistent watering is crucial, especially during their early growth stages and during prolonged dry spells. In our dry Mountain West climate, aim to water deeply but infrequently.

During the active growing season (late spring through summer), water your sunflowers about once a week, providing about 1-2 inches of water each time. Use the "finger test" to check the soil moisture: if the top 2 inches of soil feel dry, it's time to water. Water at the base of the plants to avoid wetting the foliage, which can lead to fungal issues in some seasons.

Signs of underwatering include wilting leaves and stunted growth. Overwatering can lead to root rot, so make sure the soil is well-draining. A layer of mulch around the base of your sunflower plants will help retain moisture in our dry climate and suppress weeds.

You can expect your first sunflower harvest from mid July through early October, depending on when you planted. For harvesting seeds, wait until the back of the sunflower head turns brown and the seeds are plump and somewhat loose.

To harvest the seeds, cut the entire flower head off the stalk, leaving about a foot of stem. Hang the head upside down in a well-ventilated area to dry completely. If you're growing sunflowers for cut flowers, harvest them when the petals first open. As our first frost approaches in early October, harvest any remaining sunflower heads, even if they're not fully ripe, and bring them indoors to dry.

Here are three common problems you might encounter with sunflowers in the Mountain West:

Birds Eating Seeds

• What it looks like: Sunflower heads with missing or pecked-at seeds. You might see birds actively feeding on the seeds.
• What causes it: Birds are attracted to the nutritious sunflower seeds. This is especially common as the seeds ripen.
• How to fix/prevent it: Cover the sunflower heads with netting or paper bags once the petals start to dry out. You can also try using bird deterrents like reflective tape or scarecrows.

Sunflower Moth

• What it looks like: Webbing on the flower heads, damaged seeds, and small caterpillars feeding on the developing seeds.
• What causes it: Sunflower moths lay their eggs on the flower heads, and the larvae feed on the seeds.
• How to fix/prevent it: Inspect your sunflower heads regularly for signs of moth activity. Remove and destroy any infested heads. You can also use Bacillus thuringiensis (Bt) as a preventative measure.

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 around your plants. Water at the base, never overhead. Copper-based fungicides can be used for prevention.

Mountain West Specific Challenges: Our moderate-at-altitude heat, low humidity, and dry climate generally reduce the risk of fungal diseases like downy mildew compared to more humid regions. However, the intense sun can stress plants if they're not watered adequately. Hail can also damage sunflower heads, so consider providing protection during severe weather events.

Sunflowers make great companions for several plants in the Mountain West garden. Cucumbers and squash benefit from the partial shade provided by sunflowers, which helps prevent sunscald in our intense UV. Green beans and corn can use sunflowers as a natural trellis. Lettuce planted near sunflowers can enjoy the shade, preventing bolting in the summer. Avoid planting potatoes near sunflowers, as they can inhibit each other's growth, likely due to competition for resources in our often alkaline soil.