Sunflower in Zone 9B — Desert Southwest

Sunflowers are a fantastic addition to any Desert Southwest garden. Not only are they beautiful and attract pollinators, but you can also harvest the seeds for a tasty snack or roasting. The height adds visual interest, and they're surprisingly drought-tolerant once established.

While our extreme heat and alkaline soil present challenges, the long growing season in our Zone 9B climate (around 313 days!) gives you ample opportunity to grow sunflowers successfully. By timing your planting right, you can enjoy these sunny blooms.

Starting sunflower seeds indoors is an option, especially if you want a head start on the season. You can start indoors from mid January through early February, about three weeks before you plan to transplant them outside. Use seed trays with a good seed-starting mix, and keep them warm and well-lit.

Bottom watering is key to prevent damping off; set the tray in a shallow dish of water and let the soil soak it up from the bottom. Given our very-early spring character in the Desert Southwest, indoor starting lets you get a jump on the season, but direct sowing is usually more straightforward.

Transplant your sunflower seedlings outdoors from mid February through mid March. Before transplanting, be sure to harden them off by gradually exposing them to outdoor conditions for about a week. This helps them adjust to the intense Desert Southwest sun.

Space your transplants 18-24 inches apart to give them plenty of room to grow. Keep an eye on the weather; even though it's usually mild, we can still get a late cold snap that could damage young plants.

Direct sowing is the preferred method for sunflowers in our region. Sow seeds directly into the ground from early February through mid September. Sunflowers are easy to direct sow and grow quickly.

Prepare the soil by loosening it and amending with compost if needed, even if caliche is present. Make sure the soil temperature is at least 60°F for best germination. Plant seeds 1-2 inches deep, spacing them 18-24 inches apart.

Sunflowers need moderate watering, but they're surprisingly drought-tolerant once established, thanks to their deep taproots. In our Desert Southwest climate, watering deeply but infrequently is the best approach. During the hottest part of summer, water established plants about once a week, giving them a good soak.

Check the soil moisture using the finger test: stick your finger into the soil about 2 inches deep. If it feels dry, it's time to water. Give them about 1-2 inches of water per week, depending on the size of the plant and rainfall. Water at the base of the plant to avoid wetting the foliage, especially during our monsoon season.

Signs of underwatering include wilting leaves and stunted growth. Overwatering can lead to root rot, indicated by yellowing leaves and a mushy stem base. Mulching around your sunflowers with organic material like straw or wood chips helps retain moisture in our arid climate.

You can expect your first sunflower harvest from late April through mid December, depending on when you planted. For harvesting seeds, wait until the back of the flower head turns brown and the seeds are plump and slightly loose. Cut the entire head off the stalk, leaving a foot or two of stem, and hang it upside down in a cool, dry place to dry completely.

If you're growing sunflowers for cut flowers, cut the stems when the petals first open. Place them immediately in water. As our first frost approaches in mid- December, harvest any remaining flower heads.

Here are some common problems you might encounter with sunflowers in the Desert Southwest:

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. Our open skies in the Desert Southwest make them easy targets.
• How to fix/prevent it: Cover the flower heads with netting or burlap bags once the petals start to dry. You can also try using bird deterrents like reflective tape or decoys.

Sunflower Moth

• What it looks like: Webbing and frass (insect droppings) on the flower head, damaged 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 flower heads regularly for signs of infestation. 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: 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.

Desert Southwest Specific Challenges: The extreme heat and low humidity in our region can stress sunflowers, making them more susceptible to pests and diseases. Sunscald can also be a problem; provide afternoon shade during the hottest months. The monsoon season can bring humidity that encourages fungal diseases, so good air circulation and proper watering are essential.

Sunflowers make great companions for several plants in the Desert Southwest garden. Cucumber and squash benefit from the partial shade that sunflowers provide during our intense summers, protecting them from sunscald. Green beans can use the sunflower stalks as a natural trellis. Corn and sunflowers are classic companions, as they both have similar nutrient needs and growth habits. Lettuce can benefit from the sunflower's shade, especially during the hotter parts of the year.

Avoid planting potatoes near sunflowers, as they can compete for the same nutrients in our often-poor soil. This competition can stunt the growth of both plants.