Arugula in Zone 6B — Mountain West

Arugula is a fantastic addition to any Mountain West garden. Its peppery flavor adds a zing to salads, sandwiches, and pizzas, and it thrives in our cool spring and fall weather. Plus, few things are more rewarding than harvesting your own fresh greens right outside your door.

Our short growing season of 163 days, intense sun, and alkaline soil can be challenging, but with a little planning, you can enjoy a steady supply of arugula from spring through fall. The key is timing your plantings to avoid the worst of the summer heat.

Starting arugula indoors is an option, but honestly, it's not usually necessary here in the Mountain West. Arugula germinates quickly and easily when direct sown, so starting indoors is generally only useful if you're itching to get a very early start or want to ensure a continuous harvest.

If you do decide to start indoors, begin in mid-March through early April, about three weeks before you plan to transplant. Use seed trays or small pots filled with a good seed-starting mix. Keep the soil consistently moist by bottom watering – set the tray in a shallow dish of water and let the soil absorb it. Provide warmth and plenty of light, especially considering how late our spring starts can be.

Transplanting arugula seedlings outdoors is best done in mid-April through late May. This allows them to establish before the heat of summer arrives. Before transplanting, harden off your seedlings by gradually exposing them to outdoor conditions for about a week.

When transplanting, space the seedlings about 6 inches apart. Be mindful of potential late frosts, which can still occur at this time of year. Protect your young plants with row covers if frost is predicted.

Direct sowing is the easiest and most common way to grow arugula in the Mountain West. You can sow seeds directly into the garden from late March through mid August, ensuring a continuous harvest. Arugula thrives in the cool weather of spring and fall, but bolts (goes to seed) quickly in the heat, so plan accordingly.

Prepare the soil by loosening it and adding compost. Sow seeds about ¼ inch deep and 6 inches apart. Keep the soil consistently moist until the seedlings emerge, usually within a week.

Arugula needs consistent moisture to thrive, especially in our dry Mountain West climate. While not drought-tolerant, it's also susceptible to bolting if stressed. Finding the right balance is key.

During the spring and fall, when temperatures are cooler, water deeply about once or twice a week, providing around 1 inch of water each time. Use the "finger test" – stick your finger about 2 inches into the soil. If it feels dry, it's time to water. In the warmer summer months, you might need to water more frequently, perhaps every other day. Our intense sun and low humidity can dry out the soil quickly.

Water at the base of the plants to avoid wetting the leaves, as this can encourage fungal diseases, though our low humidity makes this less of a concern than in other regions. Watch for signs of underwatering, such as wilting leaves, or overwatering, such as yellowing leaves. A layer of mulch, like straw or shredded leaves, can help retain moisture and keep the soil cool.

You can expect your first arugula harvest about 40 days after planting, which means you can start enjoying fresh arugula from early May through mid October, depending on your planting schedule. Harvest young leaves when they 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 continuous production throughout the season. Be sure to harvest before the plants start to flower, as the leaves will become bitter once they bolt. As the first frost approaches in early October, harvest any remaining leaves.

Here are some common problems you might encounter growing arugula in the Mountain West:

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: 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. You can also try coating the leaves with kaolin clay or spraying with neem oil. Interplanting with basil or catnip can also deter them.

Bolting in Heat

• What it looks like: The plant sends up a flower stalk. The leaves become tough and bitter.
• What causes it: Extended warm temperatures. Arugula is a cool-season crop and bolts when the days consistently exceed 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 soft-bodied insects (green, black, or white) 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.
• How to fix/prevent it: Knock them off with a strong water spray. Encourage ladybugs and lacewings. Use insecticidal soap or neem oil for heavy infestations. 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. Copper-based fungicides for prevention. Plant resistant varieties where available.

Mountain West Specific Challenges: Our moderate-at-altitude summer heat can cause arugula to bolt quickly if you're not careful. The low humidity generally helps prevent foliar diseases, but consistent watering is crucial given our dry rainfall. Also, be prepared for intense UV light, which can stress plants and intensify the peppery flavor (which may or may not be desirable).

Arugula benefits from companion planting. Lettuce and spinach are good companions because they have similar growing requirements and can provide shade for each other. Carrots and beets are also good choices, as they help to loosen the soil and improve drainage. Onions deter pests like aphids.

Avoid planting arugula near strawberries. Strawberries are susceptible to verticillium wilt, which can also affect arugula.