Arugula in Zone 7B — Pacific Northwest

Arugula is a fantastic addition to the Pacific Northwest garden. Its peppery bite adds a delicious zest to salads and sandwiches, and it's incredibly versatile in the kitchen. Plus, the satisfaction of harvesting fresh greens from your own backyard, especially when our cool nights enhance their flavor, is hard to beat.

While we enjoy mild summers, our springs can be overcast and cool, and we sometimes struggle with getting enough heat for warm-season crops. But with a 193-day growing season and careful timing, you can easily enjoy a continuous harvest of arugula throughout much of the year.

Starting arugula indoors is definitely an option, especially if you're eager to get a jump start on the season. You can start seeds indoors from early to late March, about 3 weeks before you plan to transplant them outside. Honestly, direct sowing works so well for arugula that I only start indoors if I'm trying to get an extra-early crop.

Use seed trays or small pots filled with seed-starting mix. Keep the soil consistently moist, and a little bottom watering prevents damping off. Place the trays in a warm location, ideally around 70°F, and provide supplemental light if needed – our spring days can be a bit dim.

Transplant your arugula seedlings outdoors from early April through mid May, once the soil has warmed up a bit. Before transplanting, harden off your seedlings by gradually exposing them to outdoor conditions for about a week. This helps them adjust to the sun and wind.

When transplanting, space the seedlings about 6 inches apart. Our wet springs can sometimes lead to slug problems, so be prepared to protect your young plants. Sprinkle slug bait around the base of the plants or use other slug control methods.

Direct sowing is the easiest and most common method for growing arugula in the Pacific Northwest. You can sow seeds directly into the garden from mid March through early September, ensuring a continuous supply of fresh greens. Arugula is fast-growing and germinates readily in cool soil.

Prepare the soil by loosening it and removing any weeds. Sow seeds about ¼ inch deep and 6 inches apart. Keep the soil consistently moist until the seedlings emerge. Because arugula bolts in warmer weather, succession planting every few weeks is key to a steady harvest.

Arugula needs consistent moisture to thrive, but it doesn't like to be waterlogged. In our Pacific Northwest climate, the watering schedule will vary depending on the season and rainfall. During our dry summer months, you'll need to water more frequently than during our wet springs.

Use the "finger test" to determine when to water. Stick your finger about 2 inches into the soil – if it feels dry, it's time to water. 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 in our humid springs.

Signs of underwatering include wilting leaves and slow growth. Overwatering can lead to root rot and yellowing leaves. A light layer of mulch, like straw or shredded leaves, can help retain moisture and suppress weeds, especially during our drier periods.

You can expect your first arugula harvest in late April through early November, 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, simply snip off the leaves with scissors or your fingers, being careful not to damage the plant's crown. Regular harvesting encourages continued production. As the first frost approaches in late October, you can cover your arugula with a row cover to extend the harvest for a few more weeks.

Arugula, while generally easy to grow, can encounter a few problems in the Pacific Northwest. Here are some common issues and how to address 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 that jump when disturbed.
• What causes it: Small jumping beetles that feed on leaves. They are most damaging to small, young plants, especially in spring.
• How to fix/prevent it: Use row covers to protect seedlings. Delay planting until plants are larger and more resilient. You can also try coating the leaves with kaolin clay or spraying with neem oil. Interplanting with basil or catnip might help deter them.

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. Arugula is a cool-season crop and bolts when temperatures consistently exceed 80°F.
• How to fix/prevent it: Time your plantings for cool weather in spring and fall. Choose bolt-resistant varieties. Provide shade during warm spells with shade cloth. Mulch to keep the soil cool. Harvest frequently to encourage leafy growth and delay bolting.

Aphids

• What it looks like: Clusters of tiny green, black, or white insects on stems and leaf undersides. You might also see sticky honeydew residue and curled or distorted new growth.
• What causes it: Rapidly reproducing sap-sucking insects. Populations can explode in warm weather, and ants often protect them.
• 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, as it attracts aphids.

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: 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 by spacing plants adequately. Water at the base, never overhead. Consider copper-based fungicides for prevention, especially during wet springs. Plant resistant varieties if available.

Pacific Northwest Specific Challenges: Our mild summers and dry-summer rainfall pattern can actually be beneficial for arugula, reducing the risk of fungal diseases compared to more humid regions. However, late blight is not a major concern for arugula (it primarily affects tomatoes and potatoes), and our springs can be cool enough to slow growth. Also, be mindful of slugs, especially with young seedlings.

Arugula benefits from companion planting in the Pacific Northwest garden. Lettuce and spinach are good companions because they share similar growing requirements and don't compete for resources. Carrots and beets are also beneficial, as they help loosen the soil and improve drainage, which is especially helpful during our wet springs. Onions deter pests like aphids, protecting your arugula from infestation.

Avoid planting arugula near strawberries. Strawberries can attract slugs, which can then move on to your arugula. Keeping these plants separated can help minimize slug damage, a common concern in our moist PNW environment.