Arugula in Zone 9A — Desert Southwest

Arugula is a fantastic addition to your Desert Southwest garden, offering a peppery kick to salads, pizzas, and more. Its quick growth and adaptability to our two growing seasons mean you can enjoy fresh greens even with our challenging climate.

Sure, desert gardening comes with extreme heat and alkaline soil, but with smart timing, arugula thrives here. Our long 298-day growing season gives you ample opportunity to plant and harvest this tasty green, especially if you take advantage of the monsoon moisture.

Starting arugula indoors isn't essential in our climate, but it can give you a head start, especially for an early spring harvest. Sow seeds indoors in early to late January, about three weeks before you plan to transplant.

Use seed trays with a good seed-starting mix and keep them warm and consistently moist; bottom watering prevents damping off. Remember, spring comes early here, so getting those seeds going indoors can mean an earlier harvest.

Transplant your arugula seedlings outdoors in early February through mid March. This avoids the worst of our winter cold snaps and gives them time to establish before the extreme heat hits.

Harden off your seedlings for about a week, gradually exposing them to the sun and wind. Plant them about 6 inches apart in well-draining soil. Even in February, watch for unexpected temperature swings and protect young plants if needed.

Direct sowing arugula is the easiest method, and it works well for most of our growing season. Sow seeds mid January through mid October, taking advantage of our mild winters and extended fall.

Prepare your soil by loosening it and adding compost. Sow seeds about ¼ inch deep and keep the soil consistently moist. Arugula bolts in the heat, so focus on planting during cooler periods for best results. Space plants about 6 inches apart.

Arugula needs consistent moisture, especially in our arid climate. While it's not drought-tolerant, proper watering is key for summer survival.

During the cooler spring and fall months, aim for about 1 inch of water per week, increasing to 1.5-2 inches during the hottest parts of the year. Use the finger test: if the top 2 inches of soil are dry, it's time to water. With our low humidity, watering at the base of the plants is ideal to avoid fungal issues.

Signs of underwatering include wilting and slow growth, while overwatering can lead to yellowing leaves. A light layer of organic mulch, like composted leaves, can help retain moisture and regulate soil temperature. Especially during the monsoon, watch for root rot caused by prolonged wet conditions.

You can expect your first arugula harvest in late February through mid December, 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, snip off the outer leaves, leaving the inner ones to continue growing. This encourages continuous production. As our first frost approaches in early December, harvest any remaining leaves to enjoy before the cold sets in.

Flea Beetles

• What it looks like: Tiny round holes (shot-hole pattern) in the leaves, especially on young seedlings. You might see small, dark beetles jumping when you disturb the plant.
• What causes it: Flea beetles are attracted to young, tender plants. The dry conditions of our Desert Southwest can stress plants, making them more susceptible.
• How to fix/prevent it: Use row covers to protect seedlings. Delay planting until plants are larger and more resilient. You can also try spraying with neem oil or interplanting with basil or catnip to deter them.

Bolting in Heat

• What it looks like: The plant sends up a flower stalk prematurely. The leaves become tough and bitter, making them less palatable.
• What causes it: Arugula is a cool-season crop, and our extreme heat triggers bolting. Extended periods above 80°F will cause it to bolt.
• How to fix/prevent it: Time your plantings for spring and fall when temperatures are cooler. Choose bolt-resistant varieties. Provide shade during the hottest part of the day using shade cloth. Mulch around the plants to keep the soil cool.

Aphids

• What it looks like: Clusters of tiny green, black, or white insects on the stems and undersides of leaves. You might also notice a sticky honeydew residue and curled or distorted new growth.
• What causes it: Aphids thrive in warm weather and can quickly multiply. They suck sap from the plants, weakening them.
• How to fix/prevent it: A strong spray of water can dislodge aphids. Encourage beneficial insects like ladybugs and lacewings, which are natural predators. For heavy infestations, use insecticidal soap or neem oil.

Downy Mildew

• What it looks like: Yellow patches on the upper leaf surface with fuzzy gray-purple growth on the undersides. Leaves will eventually brown and die, starting from the bottom of the plant.
• What causes it: Downy mildew is a fungal disease that thrives in cool, humid conditions. While our climate is generally dry, monsoon season can create the perfect environment for it.
• How to fix/prevent it: Remove affected leaves immediately. Improve air circulation around the plants. Water at the base to avoid wetting the foliage. Copper-based fungicides can be used as a preventative measure.

Desert Southwest Specific Challenges: Our extreme heat and low humidity can stress arugula, making it more susceptible to pests and diseases. The monsoon season, while providing needed moisture, can also create conditions favorable for fungal diseases like downy mildew. Consistent monitoring and proactive measures are key to success.

Arugula benefits from companion planting, especially in our challenging climate. Lettuce and spinach make good companions because they share similar growing requirements and can provide shade, helping to keep the soil cool. Carrots and beets are also beneficial, as they don't compete for the same nutrients and can help loosen the soil. Onions deter pests like aphids.

Avoid planting arugula near strawberries. Strawberries can attract slugs and other pests that might then move onto your arugula.