Sunflower in Zone 9A — Southern California

Sunflowers practically scream summer, and in Southern California, we get a long one! Imagine towering sunflowers adding bursts of gold to your garden, their seeds providing healthy snacks, and their stalks potentially even offering support to climbing veggies. Their beauty and usefulness make them a rewarding addition to any SoCal garden.

Our region does present some challenges, like drought and the occasional heat wave, but with careful planning and water-wise techniques, you can absolutely grow thriving sunflowers. Our long, warm growing season—nearly year-round—gives you ample time to get them established and enjoy their splendor. Plus, you can direct sow well into summer.

Starting sunflower seeds indoors isn't usually necessary in our climate, since we can direct sow for so much of the year. However, if you want a very early start, you can begin seeds indoors from mid January through early February. This gives you a jump start of about 3 weeks before transplanting, which can be helpful if you want blooms as early as possible.

Use seed trays or small pots filled with a good quality seed-starting mix. Keep the soil consistently moist, using bottom watering to avoid disturbing the seeds. Place the trays in a warm spot with plenty of light, either a sunny windowsill or under grow lights. Since our spring can arrive very early, keep an eye on the weather and be ready to harden off your seedlings.

Transplant your sunflower seedlings outdoors from early February through early March, after they've developed a few sets of true leaves. Before planting, harden them off by gradually exposing them to outdoor conditions for about a week. This helps them adjust to the sun and wind.

Choose a sunny spot with well-draining soil and space plants 18-24 inches apart. Keep a close eye on the forecast, as we can still get occasional cool spells and even a late frost around this time. Protect young transplants if necessary.

Direct sowing is the easiest and most common way to grow sunflowers here in Southern California, thanks to our long growing season. You can sow seeds directly into the garden from early February through mid September. This gives you a huge window for succession planting and continuous blooms.

Prepare the soil by loosening it and amending with compost. Sunflower seeds need a soil temperature of at least 50°F to germinate, so wait until the soil has warmed up a bit. Plant seeds about 1 inch deep and space them 18-24 inches apart. Keep the soil consistently moist until the seedlings emerge, which should take about a week or two. Sunflowers are quick growers, so you'll see results fast!

Sunflowers are moderately drought-tolerant once established, but they still need regular watering, especially during our hot, dry summers. The key is to water deeply but infrequently, encouraging deep root growth.

During the cooler months (spring and fall), water about once a week, providing about 1 inch of water. During the summer heat inland, increase watering to twice a week, ensuring the soil is moistened several inches deep. Use the finger test: stick your finger about 2 inches into the soil. If it feels dry, it's time to water.

Water at the base of the plants to avoid wetting the foliage, which can encourage fungal diseases in our climate, even with low-to-moderate humidity. Signs of underwatering include wilting leaves and stunted growth. Overwatering can lead to root rot, so make sure the soil drains well. Adding a layer of mulch around the base of the plants helps retain moisture and suppress weeds, which is especially useful during our dry spells.

In Southern California, you can expect your first sunflower harvest from late April through mid December, depending on when you planted. Sunflowers typically take about 80 days to mature.

For harvesting seeds, wait until the back of the flower head turns brown and the seeds are plump and slightly loose. You can cover the head with cheesecloth or a paper bag to protect it from birds. For cut flowers, harvest when the petals first open. Cut the stem at an angle and place it in water immediately.

As our first frost approaches in mid- December, you can still harvest seeds from any remaining sunflowers. Cut the heads and hang them upside down in a cool, dry place to finish drying. Even if the plant isn't fully mature, you can still salvage some seeds.

Here are some common problems you might encounter growing sunflowers in Southern California:

Birds Eating Seeds

• What it looks like: Sunflower heads with missing or damaged seeds. You might see birds pecking at the flowers.
• What causes it: Birds love sunflower seeds! They're a readily available food source, especially during our dry seasons.
• How to fix/prevent it: Cover the sunflower heads with netting, cheesecloth, or paper bags as the seeds mature. You can also try using bird deterrents like reflective tape or decoys.

Sunflower Moth

• What it looks like: Small caterpillars tunneling through the sunflower head, feeding on the seeds. You might see webbing or frass (caterpillar poop) on the flower head.
• What causes it: Sunflower moths lay their eggs on the flower heads, and the larvae hatch and burrow into the seeds.
• How to fix/prevent it: Inspect your sunflowers regularly for signs of infestation. Remove and destroy any infested flower heads. You can also use Bacillus thuringiensis (Bt), a biological insecticide, to control the caterpillars.

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: Downy mildew is caused by an oomycete pathogen that spreads in cool, humid conditions via wind-carried spores. While SoCal isn't known for humidity, our winter-wet weather can create favorable conditions.
• 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. Plant resistant varieties where available.

Southern California Specific Challenges: Our hot summers and low-to-moderate humidity can stress sunflowers, making them more susceptible to pests and diseases. The Santa Ana winds can also damage tall plants, so provide support if necessary. During fire season, be extra vigilant about watering and keeping your garden clear of dry debris.

Sunflowers can be great companions for other plants in your Southern California garden.

• Cucumber and Squash: These sprawling plants can benefit from the shade provided by sunflowers during our intense summer heat inland. The sunflowers also attract pollinators that will help with fruit production.
• Green Beans: Beans are nitrogen fixers, which means they can improve the soil quality for the sunflowers. Plus, the sunflowers can provide support for the bean vines to climb.
• Corn: Sunflowers and corn are often grown together, as they both have similar needs and can help each other with pollination.
• Lettuce: Plant lettuce near the base of sunflowers. The sunflowers provide shade for the lettuce, preventing it from bolting in the heat.

Avoid planting potatoes near sunflowers, as they can compete for nutrients in the soil.