Arugula in Zone 8B — Pacific Northwest

Arugula, with its peppery bite, is a fantastic addition to any Pacific Northwest garden. It thrives in our mild summers and cool nights, adding zest to salads, pizzas, and more. The satisfaction of harvesting fresh greens just weeks after planting is hard to beat.

While we might struggle with heat-loving plants, arugula relishes our long, mild growing season. You can easily work around our wet springs and any short bursts of heat, fitting multiple harvests into our roughly 210-day growing season. Careful timing helps you dodge the worst of the weather.

Starting arugula indoors is an option, though not always necessary given how well it direct sows. If you want a very early start, aim to sow seeds indoors from late February through mid March, about three weeks before your target transplant date. Use seed trays with a good seed-starting mix, provide gentle warmth, and ensure they get plenty of light, especially with our overcast spring days.

Bottom watering is a great way to keep the soil moist without overwatering the delicate seedlings. While it's an option, direct sowing often works just as well in our climate.

Transplant your arugula seedlings outdoors from late March through early May. Before transplanting, be sure to harden them off by gradually exposing them to outdoor conditions for about a week. This helps them adjust to the cooler temperatures and stronger sunlight.

Space the seedlings about 6 inches apart in well-drained soil. Keep an eye on the weather, as late frosts can still occur during this time. Covering the young plants with horticultural fleece can provide extra protection if a cold snap is predicted.

Direct sowing arugula is a breeze in our Pacific Northwest climate. Sow seeds directly into the garden from early March through early September. This gives you plenty of opportunity for succession planting.

Prepare the soil by loosening it and removing any weeds. Arugula germinates best when the soil is cool, around 50-65°F. Sow seeds about ¼ inch deep and 6 inches apart. Keep the soil consistently moist, and you should see seedlings emerge within a week. The biggest challenge with direct sowing is that arugula tends to bolt (go to seed) in hot weather, so focus on spring and fall plantings.

Arugula needs consistent moisture to thrive, but it's also important to avoid overwatering, which can lead to problems. In our Pacific Northwest climate, where summers are mild and rainfall is common, watering needs careful attention. During the wet springs, you might not need to water at all, relying on natural rainfall.

Use the "finger test" to check soil moisture: stick your finger about 2 inches deep into the soil. If it feels dry, it's time to water. During the dry summer months, aim for about 1 inch of water per week, either from rainfall or irrigation. Water at the base of the plants to avoid wetting the leaves, which can encourage fungal diseases, although this is less of a concern with our dry-summer humidity.

Underwatering can cause the leaves to become tough and overly peppery, while overwatering can lead to yellowing leaves and root rot. A light layer of mulch, such as straw or wood chips, can help retain moisture and keep the soil cool, which is especially beneficial during warmer periods.

You can expect your first arugula harvest from mid April through early November, about 40 days after planting. The flavor changes with leaf size. Harvest young leaves when they are 2-3 inches long for a milder flavor, or wait until they are larger for a more intense, peppery taste.

Harvest arugula by snipping off the outer leaves, leaving the inner leaves to continue growing. This encourages continuous production throughout the season. Be sure to harvest before the plant starts to flower, as bolting makes the leaves bitter.

As the first frost approaches in early November, harvest any remaining leaves to enjoy a final taste of your garden. You might be surprised at how long it produces in our mild fall weather.

Arugula, while easy to grow, can sometimes face challenges in the Pacific Northwest. Here are some common problems and how to deal with 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: These small jumping beetles feed on the leaves, causing damage. They are most problematic for small, young plants.
• How to fix/prevent it: Use row covers to protect seedlings during their vulnerable stage. Delay planting until plants are larger and more resilient. Kaolin clay coating can also deter them. Consider 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.
• How to fix/prevent it: Time your plantings for cool weather in spring and 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, soft-bodied insects (green, black, or white) on stems and leaf undersides. You might also notice sticky honeydew residue and curled or distorted new growth.
• What causes it: Aphids are sap-sucking insects that reproduce rapidly, especially in warm weather.
• How to fix/prevent it: Knock them off with a strong spray of water. Encourage natural predators like ladybugs and lacewings. Use insecticidal soap for heavy infestations or neem oil for a systemic approach. 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: A fungal disease 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, avoiding overhead watering. Consider copper-based fungicides for prevention.

Pacific Northwest Specific Challenges: Our mild heat and dry-summer rainfall pattern means that bolting is less of a problem than in hotter climates, but downy mildew can still be a concern, especially during our wet springs. Slugs can also be an issue, especially for young seedlings.

Arugula benefits from companion planting in the Pacific Northwest garden. Plant it alongside lettuce and spinach, as they share similar growing requirements and won't compete for resources. Carrots and beets make good companions because they help loosen the soil, which arugula appreciates.

Onions are also beneficial, as their strong scent can deter pests like flea beetles. Avoid planting arugula near strawberries, as they can attract aphids, which can then spread to your arugula.