Sunflower in Zone 8A — Pacific Northwest

Sunflowers bring a burst of sunshine to your garden and offer a rewarding harvest of tasty seeds. In our mild summers and cool nights, the flavor of those seeds intensifies, and the towering beauty of the plants is a welcome sight. Plus, they're great for attracting pollinators!

While sunflowers are relatively easy to grow, we do have some regional challenges to consider. Cool soil in spring can slow things down, and late blight is always a concern. But with our long, mild fall and a 203-day growing season, you have plenty of time to get a great harvest.

Starting sunflower seeds indoors gives you a head start, but it's generally not necessary. Sunflowers prefer direct sowing and resent transplanting if their roots are disturbed. However, if you're eager to get a jump on the season or want to ensure germination in cool soil, you can start them indoors.

Start seeds indoors from mid-March through early April, about three weeks before you intend to transplant. Use seed trays or small pots filled with a good seed-starting mix. Keep them warm (around 70°F) and provide plenty of light, either from a sunny windowsill or a grow light. Bottom watering will help prevent damping off – just set the tray in a shallow dish of water and let the soil absorb it. Remember, our spring weather can be slow to warm up, so be patient!

Transplant your sunflower seedlings outdoors from mid-April through mid-May, once the soil has warmed up a bit. Before transplanting, harden off your seedlings by gradually exposing them to outdoor conditions for about a week. Start with an hour or two of shade and increase the time each day.

Choose a sunny spot with well-drained soil. Space your sunflower seedlings 18-24 inches apart to give them plenty of room to grow. Keep an eye on the weather forecast – those overcast spring days can still bring a late frost, so be prepared to cover your seedlings if needed.

Direct sowing is the preferred method for growing sunflowers. They're easy to start from seed and grow quickly once the soil warms up. Sow sunflower seeds directly into your garden from early April through late July for a continuous succession of blooms.

Choose a location that gets full sun (at least 6-8 hours a day). Prepare the soil by loosening it and amending with compost. Sow seeds 1 inch deep and 18-24 inches apart. Keep the soil consistently moist until the seedlings emerge, which usually takes about a week.

Sunflowers are moderately drought-tolerant once they're established, thanks to their deep taproot. However, they do need regular watering, especially during dry spells. Our mild summers and dry summer months mean that consistent watering is key to healthy growth.

During the wet springs, you likely won't need to water much at all. But once the dry summer months arrive, check the soil moisture regularly. Use the "finger test" – stick your finger into the soil about 2 inches deep. If it feels dry, it's time to water. Aim to give your sunflowers 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 dry-summer climate. Signs of underwatering include wilting leaves and stunted growth. Overwatering can lead to root rot, so make sure your soil is well-draining. Adding 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 June through late October, depending on when you planted them. Sunflowers are ready to harvest for seeds when the back of the head turns brown and the seeds are plump.

To harvest the seeds, cut the entire flower head off the stalk, leaving about a foot of stem attached. Hang the flower head upside down in a dry, well-ventilated place to dry completely. You can then rub the seeds out of the head. For cut flowers, harvest when the petals first open, cutting the stem at an angle.

As the first frost approaches in late October, harvest any remaining flower heads, even if they're not fully ripe. You can still dry the seeds indoors.

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

Birds Eating Seeds

• What it looks like: Sunflower heads stripped bare of seeds, often with birds actively feeding on the plants.
• What causes it: Birds love sunflower seeds! They're especially attracted to ripening seeds.
• How to fix/prevent it: Cover the flower heads with netting or paper bags once the seeds begin to mature. You can also try using bird netting to protect the entire planting.

Sunflower Moth

• What it looks like: Holes in the flower heads, webbing, and larvae feeding on the seeds.
• What causes it: Sunflower moths lay their eggs on the flower heads, and the larvae burrow into the seeds.
• How to fix/prevent it: Inspect your plants regularly for signs of infestation. Remove and destroy any affected flower heads. You can also try using Bacillus thuringiensis (Bt) spray 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: While our mild summers are generally favorable for sunflowers, the dry summer rainfall can sometimes lead to increased downy mildew pressure if you're not careful with watering. Be sure to provide good air circulation and avoid overhead watering.

Sunflowers make great companions for many garden plants. Cucumbers and squash benefit from the sunflowers' shade, which helps to keep the soil moist during our dry summer months. Green beans can climb up the sunflower stalks for support. Corn and sunflowers are classic companions because they don't compete for the same nutrients. Lettuce can be planted in the shade of sunflowers to prevent bolting in the summer heat.

Avoid planting potatoes near sunflowers. Potatoes are susceptible to late blight, and sunflowers can sometimes attract the disease, potentially spreading it to your potato crop.