Sunflower in Zone 6B — Pacific Northwest

Sunflowers are a rewarding addition to any Pacific Northwest garden. Their cheerful faces brighten up even our overcast spring days, and the seeds are a tasty treat for you and the birds. Plus, the cool nights we enjoy here actually enhance the flavor of the seeds.

Our mild summers and relatively short growing season (around 162 days) do present some challenges. But with a little attention to timing and variety selection, you can absolutely enjoy a bountiful sunflower harvest right here in the PNW.

Starting sunflowers indoors is possible, but not usually necessary in our region. Since they prefer direct sowing, it's best to start them indoors only if you're aiming for a super early bloom. If you want to get a jump start, begin indoors from early April through early May, about three weeks before you plan to transplant.

Use seed trays with good drainage and a light, well-draining potting mix. Bottom watering is key to prevent damping off. Place the trays in a warm spot with plenty of light – a south-facing window or under grow lights works well. Remember that our springs are slow to warm up, so supplemental heat might be needed.

Transplant your sunflower seedlings outdoors from early May through early June, after 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 cooler temperatures and stronger sunlight.

Plant them 18-24 inches apart in a sunny spot with well-drained soil. Keep an eye on the weather forecast, as late frosts can still occur in early May. Protect your young plants with row covers if a cold snap is predicted.

Direct sowing is the preferred method for growing sunflowers in the Pacific Northwest. The soil needs to be at least 60°F for successful germination, so wait until early May through early July to sow your seeds. This gives the soil a chance to warm up after our wet springs.

Prepare the soil by loosening it and adding compost or other organic matter. Plant seeds 1-2 inches deep and 18-24 inches apart. Water gently but thoroughly after planting. Sunflowers germinate quickly, and you should see seedlings emerge within a week or two.

Sunflowers are moderately drought-tolerant once established, thanks to their deep taproots. However, consistent watering is important, especially during their early growth stages and during our dry summer months. Aim to water deeply but infrequently, rather than shallowly and often.

During our wet springs, you might not need to water at all, unless we experience an unusually dry spell. Once summer arrives, check the soil moisture regularly. Stick your finger about two inches deep into the soil. If it feels dry, it's time to water. Give them about 1 inch of water per week, either from rainfall or irrigation.

Water at the base of the plants to avoid wetting the foliage, which can encourage fungal diseases in our sometimes humid conditions. Signs of underwatering include wilting leaves and slow growth. Overwatering can lead to root rot, so make sure the soil is well-draining. 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-July through early October, about 80 days after planting. For harvesting seeds, wait until the back of the flower head turns brown and the seeds are plump and slightly loose. You can also test a few seeds – they should be easy to remove and have a dark stripe.

To harvest the seeds, cut the flower head off the stalk and hang it upside down in a dry, well-ventilated place. This allows the seeds to dry completely. For cut flowers, harvest when the petals first open. Cut the stem at an angle and place the flowers in water immediately.

As our first frost approaches in early October, keep an eye on your sunflowers. If the heads are not fully ripe, you can cut them and bring them indoors to finish ripening. Place them in a warm, dry place with good air circulation.

Here are three 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 sunflower seeds as a food source.
• How to fix/prevent it: Cover the flower heads with netting or burlap bags once the seeds begin to mature. You can also try using bird deterrents, such as reflective tape or decoys.

Sunflower Moth

• What it looks like: Small caterpillars feeding on the flower head, often accompanied by webbing and seed damage.
• 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: Monitor your plants regularly for signs of infestation. Remove and destroy any affected flower heads. You can also try using 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: Oomycete pathogen that spreads in cool, humid conditions via wind-carried spores. Different species affect different plants.
• How to fix/prevent it: Remove affected leaves immediately. Improve air circulation. Water at the base, never overhead. Copper-based fungicides for prevention. Plant resistant varieties where available.

Pacific Northwest Specific Challenges: Our mild heat, dry-summer humidity, and dry-summer rainfall can create conditions that favor certain pests and diseases. While late blight is more of a tomato and potato problem, downy mildew can still be an issue with sunflowers, especially during our wetter springs. Careful monitoring and preventative measures are key to keeping your sunflowers healthy and productive.

Sunflowers make great companions for a variety of plants in the Pacific Northwest garden. Cucumbers and squash benefit from the sunflower's shade, which helps protect them from our mild but still intense summer sun. Green beans can use the sunflower stalks as a natural trellis, saving you space and providing support. Corn also thrives alongside sunflowers, as they both have similar nutrient needs.

Lettuce can be planted near sunflowers to provide shade during the hottest part of the day, preventing it from bolting. Avoid planting potatoes near sunflowers, as they can compete for nutrients and attract similar pests.