Arugula in Zone 10B — Desert Southwest

Arugula is a fantastic addition to the desert garden, offering a peppery bite that elevates salads and adds zing to cooked dishes. Its quick growth and cool-season preference align perfectly with our two growing seasons, providing fresh greens when other crops struggle in the extreme heat. Plus, homegrown arugula tastes far superior to anything you'll find at the grocery store.

Desert gardening presents unique challenges, but arugula's relatively short growing season makes it a rewarding crop here. By planting at the right time and providing adequate care, you can enjoy a continuous harvest of this flavorful green throughout our mild winters and extended fall season. Our 349-day growing season gives us plenty of time to get it right.

Starting arugula indoors is certainly possible, though direct sowing is often more practical. If you're aiming for the earliest possible harvest, or want to get a jump start, start seeds indoors in early to late December, about three weeks before you plan to transplant.

Use seed trays or small pots filled with a good seed-starting mix. Keep the soil consistently moist by bottom watering to avoid damping off. Place the trays in a warm location with plenty of light, either from a sunny window or a grow light. Given our very-early spring character, any head start you can give your plants is a plus.

Transplant your arugula seedlings outdoors in early January through mid February, once they have a few sets of true leaves. Before transplanting, harden them off by gradually exposing them to outdoor conditions for about a week. This is crucial to prevent shock, especially considering the temperature swings we can experience during that time of year.

Space the seedlings about 6 inches apart in well-drained soil. Keep in mind that unexpected cold snaps can happen, so be prepared to cover your transplants if temperatures dip unexpectedly.

Direct sowing arugula is a breeze, especially in our mild winter climate. Sow seeds mid December through early November, directly into well-prepared soil. Arugula prefers soil temperatures between 45°F and 70°F for optimal germination.

Lightly cover the seeds with soil and keep the area consistently moist. Thin the seedlings to about 6 inches apart once they emerge. Direct sowing is a great option because arugula grows quickly, but be mindful of bolting if you plant too late in the spring or too early in the fall.

Arugula needs consistent moisture to thrive, especially in our arid climate. While it's not drought-tolerant, proper watering is key to preventing bolting and maintaining good flavor.

During the cooler months (late fall through early spring), water deeply about once or twice a week, providing about 1 inch of water each time. Use the finger test – if the top 2 inches of soil feel dry, it's time to water. During monsoon season, monitor rainfall and adjust your watering schedule accordingly.

Water at the base of the plants to avoid wetting the leaves, which can encourage fungal diseases despite our low humidity. Signs of underwatering include wilting leaves and a strong, bitter taste. Overwatering can lead to root rot, so ensure good drainage. Applying a layer of organic mulch, like compost, can help retain moisture and regulate soil temperature.

You can expect your first harvest of arugula in late to early January, about 40 days after planting. Harvest young leaves when they are 2-3 inches long for a milder flavor. Larger leaves will have a more pronounced peppery taste.

To harvest, simply snip off the outer leaves with scissors, leaving the inner leaves to continue growing. This cut-and-come-again method will provide a continuous harvest throughout the season. Be sure to harvest before the plant starts to flower, as bolting will make the leaves bitter.

As the first frost approaches in late December, you can extend your harvest by covering the plants with a frost blanket on cold nights. Even with a light frost, the leaves will bounce back quickly, but if you do get a surprise cold snap, harvest what you can before it hits.

Arugula, like any crop, can face challenges in the Desert Southwest. Here are four common problems and how to address them:

Flea Beetles

• What it looks like: Tiny round holes (shot-hole pattern) in leaves, especially on young seedlings. You might see small dark beetles jumping when disturbed.
• What causes it: Small jumping beetles that feed on leaves. They thrive in warm, dry conditions, making them a common pest in our spring and fall.
• How to fix/prevent it: Use row covers to protect seedlings during their vulnerable stage. Delay planting until plants are larger. Consider a kaolin clay coating or neem oil spray. Interplant with basil or catnip to deter them.

Bolting in Heat

• What it looks like: The plant sends up a flower stalk, and the leaves become tough and bitter.
• What causes it: Extended warm temperatures. Arugula is a cool-season crop, and our rapid temperature swings can trigger bolting.
• How to fix/prevent it: Time your plantings for the cooler parts of the year. Choose bolt-resistant varieties. Provide shade during warm spells with shade cloth, which is essential for summer survival here. Mulch to keep the soil cool. Harvest frequently to encourage continued leaf production.

Aphids

• What it looks like: Clusters of tiny green, black, or white insects on stems and leaf undersides. Sticky honeydew residue and curled or distorted new growth.
• What causes it: Rapid-reproducing sap-sucking insects that thrive in warm weather.
• How to fix/prevent it: Knock them off with a strong water spray. Encourage beneficial insects like ladybugs and lacewings. Use insecticidal soap or neem oil for heavy infestations.

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. While our humidity is generally low, monsoon moisture can create favorable conditions for downy mildew.
• How to fix/prevent it: Remove affected leaves immediately. Improve air circulation by spacing plants adequately. Water at the base, never overhead. Copper-based fungicides can be used for prevention.

Desert Southwest Specific Challenges: The extreme heat and intense sun of the Desert Southwest can quickly stress arugula, leading to bolting and sunscald. Even though our humidity is low, the monsoon season can create conditions favorable for fungal diseases. Careful monitoring and proactive measures are crucial for success.

Arugula benefits from companion planting. Lettuce and spinach are good companions because they share similar growing requirements and don't compete for resources. Carrots and beets loosen the soil, making it easier for arugula roots to grow. Onions deter pests and can help improve the overall health of your arugula.

Avoid planting arugula near strawberries. Strawberries can attract pests that also affect arugula, increasing the risk of infestation. By choosing the right companions, you can create a healthier and more productive garden, even in our challenging climate.