Arugula in Zone 6A — Pacific Northwest

Arugula is a fantastic addition to any Pacific Northwest garden. Its peppery bite adds zing to salads, pizzas, and pesto, and the cool nights we get here actually enhance its flavor. Plus, it's incredibly satisfying to harvest fresh greens just weeks after planting.

Our mild summers and wet springs can present a few challenges, but with a little planning, you can enjoy a continuous harvest of arugula. Our 148-day growing season is more than enough time to get multiple crops in, especially since arugula is a cool-season superstar.

Starting arugula indoors isn't essential here in the PNW, but it can give you a head start, especially if we're having a particularly wet spring. If you want to get a jump on the season, start your seeds indoors from late March through mid April, about three weeks before you plan to transplant them.

Use seed trays with a good seed-starting mix and keep them in a warm spot with plenty of light – a sunny windowsill or under grow lights works well. Make sure to keep the soil consistently moist; bottom watering is a great way to prevent damping off. Remember, our overcast spring days can mean seedlings need supplemental light to prevent legginess.

Transplant your arugula seedlings outdoors from late April through early June, once the soil has warmed up a bit. Before planting, 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 your arugula plants about 6 inches apart in a well-prepared bed. Keep an eye on the weather forecast – a late frost can still happen, so be ready to cover your seedlings if necessary.

Direct sowing arugula is the easiest way to grow it in our climate. Since it's quick to germinate and mature, you can sow seeds directly into the garden from mid April through mid August for a continuous supply. The key is to keep the soil consistently moist, especially during germination.

Prepare your soil by loosening it and adding some compost. Sow the seeds about ¼ inch deep and 6 inches apart. Arugula bolts in the heat, so planting during cooler periods will result in the best flavor and prevent premature flowering.

Consistent watering is crucial for happy arugula plants, especially during our dry summer months. While we may get decent rainfall in the spring, it's important to monitor the soil moisture as things dry out. Arugula isn't drought-tolerant, and dry conditions can stress the plants and make the leaves taste overly peppery.

A good rule of thumb is to check the soil moisture about 2 inches deep – if it feels dry, it's time to water. Aim for about 1 inch of water per week, either from rainfall or irrigation. Watering at the base of the plants is best to avoid wetting the leaves, which can lead to fungal problems in our climate.

Signs of underwatering include wilting leaves and slow growth, while overwatering can cause yellowing leaves and root rot. Applying a layer of mulch, like straw or wood chips, can help retain moisture and keep the soil cool during the warmer months.

You can expect your first arugula harvest in late May through mid October, about 40 days after planting. The leaves are ready to harvest when they are 2-3 inches long for a milder flavor, or larger for a more peppery taste. The choice is yours!

To harvest, simply snip off the outer leaves with scissors or your fingers, leaving the inner leaves to continue growing. This cut-and-come-again method will provide you with a continuous supply of fresh arugula throughout the season. Be sure to harvest before the plants start to flower, as the leaves will become bitter once they bolt.

As our first frost approaches in early October, you can extend the harvest by covering your arugula with a cold frame or row cover. This will protect the plants from frost and allow you to enjoy fresh greens for a few more weeks.

Arugula, like any plant, can have its share of problems, even here in the PNW. Here are some common issues you might encounter:

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 around when disturbed.
• What causes it: These small jumping beetles feed on the leaves, causing significant damage to young plants. They thrive in dry conditions, which can be common during our dry summers.
• How to fix/prevent it: Protect seedlings with row covers. Delay planting until plants are larger and more resilient. You can also try spraying with kaolin clay or neem oil. Interplanting with basil or catnip can 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: Arugula is a cool-season crop and bolts (goes to seed) when temperatures rise consistently above its comfort zone. Even our mild summers can trigger bolting if the plants are stressed.
• How to fix/prevent it: Time your plantings for cooler weather in spring and fall. Choose bolt-resistant varieties. Provide shade during warm spells, and mulch to keep the soil cool. Harvest frequently to encourage continued leaf production.

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: 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. Insecticidal soap or neem oil can be used for heavy infestations. Avoid over-fertilizing with nitrogen, as this attracts aphids.

Downy Mildew

• What it looks like: Yellow patches on the upper leaf surface with fuzzy gray-purple growth on the undersides. Leaves will eventually brown and die from the bottom up.
• What causes it: This fungal disease thrives in cool, humid conditions, which we often experience in the spring and fall.
• How to fix/prevent it: Remove affected leaves immediately. Improve air circulation by spacing plants properly. Water at the base of the plants, avoiding overhead watering. Copper-based fungicides can be used preventatively.

Pacific Northwest Specific Challenges: While late blight isn't a huge concern for arugula itself, the conditions that favor blight (cool, wet weather) can also promote downy mildew on arugula. Slugs can also be a nuisance, especially in wet springs. Use slug bait or other control methods to protect your seedlings.

Arugula is a friendly plant that gets along with many garden companions. Lettuce and spinach make good neighbors because they share similar growing requirements and don't compete for resources. Carrots and beets are also beneficial companions, as they help to loosen the soil and improve drainage, creating a better environment for arugula's roots.

Onions can help deter pests like aphids and flea beetles, protecting your arugula from damage. Avoid planting arugula near strawberries, as they can attract slugs, which can then feast on your arugula leaves.