Sunflower in Zone 6A — Pacific Northwest

Sunflowers are a rewarding addition to any Pacific Northwest garden. Their towering presence and bright blooms bring cheer, and the seeds offer a tasty treat for both you and the local birds. Plus, the cool nights we get here enhance the flavor of the seeds.

While our mild summers and wet springs can present some challenges, sunflowers are surprisingly well-suited to our 148-day growing season. With a little attention to timing, you can enjoy these beauties from late summer into fall.

Starting sunflower seeds indoors is possible, but generally not necessary given how well they direct sow. If you're eager to get a head start or have particularly late springs, start seeds indoors from mid-April through early May, about three weeks before you plan to transplant. Use seed trays with good drainage and provide warmth and plenty of light – a south-facing window or grow lights work well.

Be sure to keep the soil consistently moist, and bottom watering will help prevent damping-off. Remember that our overcast spring days can make indoor starts leggy without supplemental light.

Transplant your sunflower seedlings outdoors from mid-May through mid-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 helps them adjust to the sun and wind.

Space them 18-24 inches apart to allow for adequate growth. Keep an eye on the weather forecast – a late cold snap can still happen, so be prepared to cover your young plants if needed.

Direct sowing is the easiest and most common method for growing sunflowers in the Pacific Northwest. Sow seeds from early May through early July, once the soil has warmed up a bit. Sunflowers germinate best when the soil temperature is consistently above 60°F.

Prepare the soil by loosening it and adding some compost. Plant seeds about 1 inch deep and space them 18-24 inches apart. Water gently after sowing, and keep the soil consistently moist until the seedlings emerge.

Sunflowers are drought-tolerant once established, thanks to their deep taproot, but they still need consistent watering, especially during our dry summer months. In the Pacific Northwest, a good rule of thumb is to water deeply but infrequently. During the dry-summer months, aim for about 1 inch of water per week.

Use the "finger test" to check soil moisture: stick your finger about 2 inches deep into the soil. 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 our dry-summer humidity.

Signs of underwatering include wilting leaves, while overwatering can lead to yellowing leaves and root rot. A layer of mulch around the base of the plants will help retain moisture and suppress weeds.

You can expect your first sunflower harvest from late July through early October, depending on when you planted and the specific variety. For seeds, wait until the back of the flower head turns brown and the seeds are plump and starting to loosen. You can then cut the entire head off and hang it upside down in a dry, well-ventilated place to dry completely.

For cut flowers, harvest when the petals first open. As the first frost approaches in early October, harvest any remaining flower heads, even if they're not fully mature. You can bring them indoors to dry or enjoy them as cut flowers.

Here are some common problems you might encounter with sunflowers in the Pacific Northwest:

Birds Eating Seeds

• What it looks like: Missing seeds from the flower head, often with signs of pecking.
• What causes it: Birds are attracted to the seeds as a food source.
• How to fix/prevent it: Cover the flower heads with netting or burlap bags once the seeds start to mature. You can also try planting a decoy crop of sunflowers nearby to distract the birds.

Sunflower Moth

• What it looks like: Holes in the flower head, webbing, and small caterpillars feeding on the seeds.
• What causes it: Sunflower moths lay their eggs on the flower heads, and the larvae burrow in and feed on the developing seeds.
• How to fix/prevent it: Inspect flower heads regularly for signs of infestation. Remove and destroy any affected heads. You can also use insecticidal soap or Bacillus thuringiensis (Bt) to control the 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.

Pacific Northwest Specific Challenges: Our dry-summer humidity can still create favorable conditions for fungal diseases like downy mildew, so good air circulation and proper watering techniques are crucial. While late blight is more of a concern for tomatoes and potatoes, it's always good practice to keep an eye out for any unusual leaf spots and remove affected foliage promptly.

Sunflowers make great companions for several plants in the Pacific Northwest garden. Cucumbers and squash benefit from the sunflower's shade, which helps protect them from the intense summer sun, especially when we get those (rare) days above 90°F. Green beans climb up the sunflower stalks, saving space and providing nitrogen to the soil. Corn also benefits from the sunflower's support, and lettuce can be planted in the sunflower's shade to prevent bolting. Avoid planting potatoes near sunflowers, as they can compete for nutrients and increase the risk of blight.