Arugula in Zone 7B — Northern California

Arugula is a fantastic addition to any Northern California garden. Its peppery bite adds a unique flavor to salads and other dishes, and it thrives in our Mediterranean climate with its long growing season. Plus, it's incredibly satisfying to harvest fresh greens from your garden nearly year-round.

While we face challenges like drought and occasional heat waves, the timing of your arugula plantings is key to success. With our extended 245-day growing season, you can easily work around the hottest parts of summer and enjoy a steady supply of this delicious green.

Starting arugula indoors is an option, especially for a very early spring harvest, but direct sowing is generally easier. If you want a head start, begin your seeds indoors from early to late February, about 3 weeks before you plan to transplant. Use seed trays filled with good quality potting mix and keep them consistently moist with bottom watering to avoid disturbing the seeds.

Provide warmth and plenty of light – a sunny windowsill or grow lights work well. Given our early spring warmth, you might find that direct sowing catches up quickly, but indoor starting can give you a jump if you're eager for those first spring salads.

Transplant your arugula seedlings outdoors from early March through mid April. 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.

Choose a spot with full sun to partial shade. Space the seedlings about 6 inches apart to give them room to grow. Keep an eye on the weather forecast, as late frosts can still occur during this time.

Direct sowing arugula is the most common and straightforward method in Northern California. Sow seeds from mid February through late September for a continuous harvest. Arugula germinates best in cool soil, so spring and fall plantings are ideal.

Prepare the soil by loosening it and adding compost. Sow seeds about ¼ inch deep and 6 inches apart. Keep the soil consistently moist. Arugula is fast-growing, but it also bolts (goes to seed) quickly in hot weather, so focus on cool-season plantings.

Arugula needs consistent moisture to thrive in our dry Northern California climate. While it's not drought-tolerant, overwatering can also be problematic, especially with clay soils. The key is to find the right balance.

During the spring and fall, when temperatures are mild, aim for about 1 inch of water per week, either from rainfall or irrigation. In the hotter summer months, you may need to increase this to 1.5-2 inches per week, especially if the plants are in full sun. Use the "finger test" – if the top 2 inches of soil feel dry, it's time to water.

Water at the base of the plants to avoid wetting the leaves, which can encourage fungal diseases in our sometimes humid microclimates. Overhead watering is fine during the hottest, driest parts of summer. Mulching around your arugula plants with straw or wood chips helps retain moisture and keep the soil cool. Wilting leaves indicate underwatering, while yellowing leaves can be a sign of overwatering.

You can expect your first arugula harvest from late March through late November, depending on when you planted. Arugula is typically ready to harvest about 40 days after planting. The leaves are most flavorful when they are young and tender.

Harvest when the leaves are 2-3 inches long for a milder flavor, or let them grow larger for a more peppery taste. To harvest, simply snip off the outer leaves with scissors or a knife, leaving the inner leaves to continue growing. This encourages continued production.

As the first frosts approach in mid- November, harvest any remaining arugula leaves. You can also cover the plants with a frost blanket to extend the harvest for a few more weeks, but the cold will eventually slow growth significantly.

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

Flea Beetles

• What it looks like: Tiny round holes (shot-hole pattern) in leaves. You'll see small, dark beetles that jump when disturbed. Seedlings are most vulnerable.
• What causes it: These small jumping beetles feed on arugula leaves, especially young plants.
• How to fix/prevent it: Use row covers to protect seedlings. Delay planting until plants are larger and stronger. You can also try coating the leaves with kaolin clay. Neem oil spray can help, as well as interplanting with basil or catnip.

Bolting in Heat

• What it looks like: The plant sends up a flower stalk, and the leaves become tough and bitter.
• What causes it: Arugula is a cool-season crop that bolts when temperatures rise consistently above its comfort zone.
• How to fix/prevent it: Time your plantings for cooler weather in spring and fall. Choose bolt-resistant varieties if available. Provide shade during warm spells with shade cloth. Mulch to keep the soil cool. Harvest leaves frequently to delay bolting.

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: These sap-sucking insects reproduce rapidly, especially 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, which are natural predators. Use insecticidal soap for heavy infestations. Neem oil also works well. Avoid excess nitrogen fertilizer, as it attracts aphids.

Downy Mildew

• What it looks like: Yellow patches on leaf tops with fuzzy gray-purple growth on the undersides. Leaves will brown and die from the bottom up.
• What causes it: This oomycete pathogen spreads in cool, humid conditions via wind-carried spores.
• How to fix/prevent it: Remove affected leaves immediately. Improve air circulation around the plants. Water at the base, avoiding overhead watering. Copper-based fungicides can be used preventatively.

Northern California Specific Challenges: Our moderate-to-hot summers and dry conditions can stress arugula, making it more susceptible to bolting and flea beetles. Consistent watering is crucial, but be mindful of overwatering in our sometimes heavy clay soils. Fire season can also impact air quality and sunlight, potentially affecting plant growth.

Arugula benefits from companion planting in a few ways. Lettuce and spinach are good companions because they have similar growing requirements and won't compete for resources. Carrots and beets are helpful because they don't take up much space above ground, allowing the arugula to get plenty of sunlight. Onions can help deter pests like aphids. Avoid planting arugula near strawberries, as they can attract pests that also affect arugula.