Arugula in Zone 10A — Southern California

Arugula is a fantastic, fast-growing green to add a peppery kick to your salads and sandwiches. The mild winters and long growing season here in Southern California mean you can enjoy a near year-round harvest of this tasty crop, adding fresh flavor to your meals even when other parts of the country are snowed in.

Sure, we have our challenges with water restrictions and the summer heat inland, but with a little planning, you can easily grow arugula successfully. Our 349-day growing season gives you plenty of opportunities to get it right.

Starting arugula indoors is definitely an option, especially if you're aiming for a very early harvest or want to get a head start. Aim to start your seeds indoors in early to late December, about three weeks before you plan to transplant.

Use seed trays with a good seed-starting mix, provide gentle warmth (a heat mat can help), and make sure they get plenty of light – a grow light is ideal. Bottom watering is key to prevent damping off; set the tray in a shallow dish of water until the soil surface is moist. Given our very-early spring character, this can give you a jump on the season.

Transplanting arugula outdoors is best done in early January through mid February, allowing it to establish before any potential heat spikes. Before transplanting, harden off your seedlings by gradually exposing them to outdoor conditions for about a week.

Space them about 6 inches apart in a well-prepared bed. Even in January, we can get some warm days, so keep a close eye on the transplants and water them regularly until they're established.

Direct sowing arugula is probably the easiest way to grow it, given how quickly it germinates. You can sow directly in the garden from mid December through early November.

Prepare your soil by loosening it and mixing in some compost. Keep the soil consistently moist until the seedlings emerge, which usually takes just a few days. Thin the seedlings to about 6 inches apart once they're a few inches tall. The downside is that it can bolt quickly in the heat, so timing is key.

Arugula needs consistent moisture to thrive, but it doesn't like to be waterlogged. During our winter-wet months, you may not need to water at all, but keep an eye on the soil. As things dry out, especially heading into spring and summer, increase your watering frequency.

A good rule of thumb is to check the soil about 2 inches deep – if it feels dry, it's time to water. Aim for about 1 inch of water per week, adjusting based on rainfall and temperature. Water at the base of the plants to avoid wetting the leaves, which can encourage fungal diseases in our low-to-moderate humidity.

Underwatering will cause the leaves to become tougher and more peppery, and can also encourage bolting. Overwatering, on the other hand, can lead to root rot. A layer of mulch will help retain moisture and keep the soil cool during warmer periods.

You can expect your first arugula harvest in late to early January, about 40 days after sowing. The leaves are usually ready to harvest when they're 2-3 inches long.

Harvest young leaves for a milder flavor, and larger leaves for a more intense, peppery taste. Pick the outer leaves, leaving the inner ones to continue growing. Regular harvesting encourages continued production. As late December approaches and our first frost is on its way, harvest any remaining leaves to enjoy before the cold weather sets in.

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 leaves, especially on young seedlings. You might see small, dark beetles jumping when you disturb the plants.
• What causes it: Small jumping beetles that feed on leaves. They're most damaging to small, young plants.
• How to fix/prevent it: Use row covers to protect seedlings. Delay planting until plants are larger. Coat plants with kaolin clay. Spray with neem oil. Interplant with basil or catnip. Healthy plants can usually outgrow the damage.

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 above 80°F.
• How to fix/prevent it: Time your plantings for cool weather (spring/fall). Choose bolt-resistant varieties. Provide shade during warm spells. Mulch to keep the soil cool. Harvest frequently to delay bolting.

Aphids

• What it looks like: Clusters of tiny green, black, or white insects on stems and leaf undersides. Sticky honeydew residue. Curled or distorted new growth.
• What causes it: Rapidly reproducing sap-sucking insects. Populations explode in warm weather. Ants may farm them for honeydew.
• How to fix/prevent it: Knock them off with a strong water spray. Encourage ladybugs and lacewings. Use insecticidal soap or neem oil. Avoid excess nitrogen fertilizer.

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.
• How to fix/prevent it: Remove affected leaves immediately. Improve air circulation. Water at the base, never overhead. Use copper-based fungicides preventatively. Plant resistant varieties.

Southern California Specific Challenges: Our hot summer heat inland, even with relatively low-to-moderate humidity, means bolting can be a major issue. Winter-wet rainfall can also increase the risk of downy mildew. Water restrictions mean you need to be efficient with your watering.

Arugula benefits from companion planting. Lettuce and spinach make good companions because they share similar growing requirements and don't compete for resources. Carrots and beets help by loosening the soil, making it easier for arugula roots to grow. Onions deter pests, which can protect your arugula from unwanted visitors. Avoid planting arugula near strawberries, as they can attract pests that also affect arugula.