Arugula in Zone 9A — Southern California

Arugula is a fantastic addition to any Southern California garden. Its peppery bite adds a unique flavor to salads, sandwiches, and pizzas, and it thrives in our mild winters and long growing season. Plus, there's nothing quite like the satisfaction of harvesting fresh greens from your own backyard all year round!

While we face challenges like drought and summer heat inland, careful timing and water-wise practices make growing arugula here very achievable. Our 322-day growing season gives you plenty of opportunities to enjoy this delicious leafy green, even with the occasional Santa Ana winds.

Starting arugula indoors in our Zone 9A climate is an option, but honestly, direct sowing is usually easier. If you want a head start, especially for an early spring harvest, start seeds indoors from late December through mid January – about 3 weeks before you plan to transplant.

Use seed trays or small pots filled with a good seed-starting mix. Keep them warm (around 65-70°F) and provide plenty of light. Bottom watering helps keep the seedlings evenly moist without encouraging fungal diseases. Since our spring comes early, this gives you a jumpstart while the ground is still cool.

Transplant your arugula seedlings outdoors from mid January through early March. Before transplanting, harden them off by gradually exposing them to outdoor conditions for about a week. This helps them adjust to the sun and wind.

Space the seedlings about 6 inches apart in well-drained soil. Keep an eye on the weather – a late cold snap can stress young transplants. If frost is forecast, cover them with row covers or blankets.

Direct sowing arugula is the most common and often the easiest method here in Southern California. You can sow seeds directly into your garden beds from early January through late October. The key is timing it around our cooler periods.

Prepare the soil by loosening it and adding compost. Arugula prefers soil temperatures between 50-70°F for optimal germination. Sow seeds about ¼ inch deep and 6 inches apart. Keep the soil consistently moist until the seedlings emerge, which usually takes about a week. Direct sowing is great, but be aware that summer heat inland can cause it to bolt quickly.

Arugula needs consistent moisture to thrive, but it doesn't like to be waterlogged. In our Southern California climate, this means adjusting your watering schedule with the seasons. During our winter-wet period, you may not need to water at all, relying on rainfall.

However, during the drier spring, summer, and fall months, water deeply whenever the top 2 inches of soil feel dry to the touch – the "finger test." Aim for about 1 inch of water per week, adjusting for rainfall and temperature. Water at the base of the plants to avoid wetting the leaves, which can increase the risk of fungal diseases, especially with our low-to-moderate humidity.

Signs of underwatering include wilting leaves and slow growth. Overwatering can lead to yellowing leaves and root rot. A layer of mulch, like straw or wood chips, can help retain moisture in the soil and regulate soil temperature, a huge help during our hot spells.

You can expect your first arugula harvest about 40 days after planting, which means from mid February through late December, depending on when you sowed. 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 or a knife, leaving the inner leaves to continue growing. This encourages continuous production. Be sure to harvest before the plant starts to flower, as the leaves will become bitter once it bolts.

As our first frost approaches in mid- December, you can extend your harvest by covering your plants with a frost blanket on cold nights. This will help protect them from damage and allow you to enjoy fresh arugula well into winter.

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

Flea Beetles

• What it looks like: Tiny round holes (shot-hole pattern) in the leaves, especially on young seedlings. You might also see small, dark beetles jumping when disturbed.
• What causes it: Flea beetles are small jumping beetles that feed on the leaves. They are most damaging to small, young plants.
• How to fix/prevent it: Use row covers to protect seedlings during their vulnerable stage. You can also delay planting until the plants are larger and more resilient. A coating of kaolin clay can deter them. Neem oil spray is also effective. Interplanting with basil or catnip can help. Healthy, vigorous plants tend to outgrow the damage.

Bolting in Heat

• What it looks like: The arugula plant sends up a flower stalk. The leaves become tough and bitter.
• What causes it: Arugula is a cool-season crop and will bolt (go to seed) when temperatures rise. Extended warm temperatures above the crop's comfort zone cause it to bolt.
• How to fix/prevent it: Time your plantings for cooler weather (spring and fall). Choose bolt-resistant varieties. Provide shade during warm spells using shade cloth. Mulch to keep the soil cool. Harvest frequently to encourage continued leaf production before bolting progresses.

Aphids

• What it looks like: Clusters of tiny soft-bodied insects (green, black, or white) on stems and leaf undersides. You might also see sticky honeydew residue and curled or distorted new growth.
• What causes it: Aphids are sap-sucking insects that reproduce rapidly. Populations explode in warm weather.
• How to fix/prevent it: A strong spray of water from the hose can knock them off. Encourage natural predators like ladybugs and lacewings. Insecticidal soap is effective for heavy infestations. Neem oil works systemically. Avoid excess nitrogen fertilizer, as it attracts them.

Downy Mildew

• What it looks like: Yellow patches on leaf tops with fuzzy gray-purple growth on the 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.
• How to fix/prevent it: Remove affected leaves immediately. Improve air circulation around the plants by spacing them properly. Water at the base of the plants, never overhead. Copper-based fungicides can be used for prevention. Plant resistant varieties where available.

Southern California Specific Challenges: Our hot, dry summers and occasional Santa Ana winds can stress arugula, making it more susceptible to bolting and flea beetle damage. Consistent watering is crucial, but be mindful of water restrictions. Fire season can also bring smoky conditions that can affect plant growth, so monitor air quality and provide extra water if needed.

Arugula plays well with several other plants in the Southern California garden. Lettuce and spinach are good companions because they have similar growing requirements and don't compete for resources. Carrots and beets help loosen the soil, making it easier for arugula roots to grow. Onions deter pests like aphids.

Avoid planting arugula near strawberries. Strawberries are susceptible to verticillium wilt, which can spread to arugula and other members of the brassica family. Keeping them separated helps prevent disease transmission.