Sunflower in Zone 8A — Desert Southwest

Sunflowers are a fantastic addition to any Desert Southwest garden. Their cheerful faces bring beauty, and you can enjoy the seeds roasted, in salads, or as snacks. Plus, they attract beneficial pollinators, which are always welcome in our gardens.

Our extreme heat and arid conditions can be tough, but with our long, 265-day growing season, you can easily time your sunflower planting for success. By planting at the right time, you'll have beautiful blooms and seeds before the worst of the summer heat hits.

Starting sunflower seeds indoors is possible, but direct sowing is generally preferred. However, if you want a head start, especially for early blooms, start seeds indoors from mid-February through early March, about three weeks before you plan to transplant. Use seed trays with good drainage and a well-draining potting mix, and keep them warm and under grow lights.

Bottom watering is ideal to prevent damping off; simply set the tray in a shallow dish of water until the soil surface is moist. Remember, our spring weather can be very-early, so keep an eye on the forecast.

Transplant your sunflower seedlings outdoors from mid-March through early April. Before transplanting, harden them off by gradually exposing them to outdoor conditions for about a week. This prevents shock and helps them adjust to the Desert Southwest sun.

Plant them 18-24 inches apart to give them plenty of room to grow. At transplant time, watch out for late cold snaps, which can stress young plants.

Direct sowing is the easiest and most common method for growing sunflowers in the Desert Southwest. Sow seeds directly into the ground from early March through late August, giving you two distinct planting windows. Choose a sunny spot with well-draining soil and ensure the soil temperature is at least 60°F.

Prepare the soil by loosening it and mixing in some compost. Plant seeds 1-2 inches deep and space them 18-24 inches apart. Sunflowers are easy to direct sow and grow quickly, so you'll be enjoying their beauty in no time!

Sunflowers are drought-tolerant once established, thanks to their deep taproot, but they appreciate consistent moisture, especially during establishment. In the Desert Southwest, a deep but infrequent watering schedule is best. During our mild spring and fall, water established sunflowers about once a week, providing 1-2 inches of water.

In the extreme summer heat, increase watering to twice a week or more, especially during our driest spells. 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 plant to avoid wetting the foliage, which can encourage fungal diseases in our occasional monsoon moisture.

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 the base of your sunflowers with organic matter like wood chips helps retain moisture and regulate soil temperature, a must in our arid climate.

You can expect your first sunflower harvest from late May through late November in the Desert Southwest, 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. You can cut the entire head and hang it upside down in a dry, well-ventilated place to finish drying.

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 late November, harvest any remaining seeds, even if they aren't fully mature, and allow them to dry indoors.

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

Birds Eating Seeds

• What it looks like: Missing seeds from the flower head, damage to developing seeds, and birds actively pecking at the sunflowers.
• What causes it: Birds are attracted to the sunflower seeds as a food source, especially when other food sources are scarce.
• How to fix/prevent it: Cover the flower heads with netting or burlap bags once the seeds begin to develop. You can also use bird feeders placed away from your sunflowers to distract them.

Sunflower Moth

• What it looks like: Small 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 hatch and feed on the developing seeds.
• How to fix/prevent it: Inspect flower heads regularly for signs of infestation. Remove and destroy any affected flower heads. Bacillus thuringiensis (Bt) can be used 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 arid humidity of the Desert Southwest can stress sunflowers, making them more susceptible to pests and diseases. Monitor your plants closely and provide adequate water, especially during the hottest months. Our monsoon season can also create periods of high humidity, increasing the risk of fungal diseases like downy mildew.

Sunflowers make great companions for several plants in the Desert Southwest garden. Cucumbers and squash benefit from the sunflower's shade, which helps protect them from sunscald. Green beans can use the sunflower stalks as a natural trellis, saving space in your garden. Corn and sunflowers are classic companions, as they both enjoy similar growing conditions. Lettuce can benefit from the partial shade provided by sunflowers, especially during the hotter months.

Avoid planting potatoes near sunflowers, as they can compete for nutrients and attract similar pests.