Arugula in Zone 5B — Mountain West

Arugula is a fantastic addition to any Mountain West garden. Its peppery bite adds a unique flavor to salads and other dishes, and it thrives in our cool spring and fall weather. Plus, there's nothing quite like the satisfaction of harvesting your own greens just minutes before they hit your plate.

Our high altitude, intense sun, and short growing season (around 149 days) can present challenges. But with careful timing and attention, you can enjoy a steady supply of fresh arugula throughout much of the year.

Starting arugula indoors is possible, but not usually necessary here. Since our springs often have temperature swings, starting indoors makes sense if you want a super early harvest. You have about a 3-week window, from late March through mid April, to start seeds indoors.

Use seed trays or small pots filled with a good seed-starting mix. Keep the soil consistently moist by bottom watering, and provide plenty of light, either from a grow light or a sunny windowsill. Remember, our late springs mean you need to be patient and protect those seedlings until the weather settles.

Transplanting arugula outdoors gives you a head start on the season. Aim to transplant in late April through early June, after the worst of the spring frosts have passed. Before transplanting, harden off your seedlings by gradually exposing them to outdoor conditions for about a week.

Space the plants about 6 inches apart in a well-prepared garden bed. Keep an eye out for late frosts, which can still happen even in late spring at our altitude, and be ready to cover your seedlings if needed.

Direct sowing arugula is the easiest way to grow it, especially given our short season. Sow seeds directly into the garden from early April through early August. Arugula germinates quickly in cool soil, so you can get multiple harvests from a single planting.

Prepare the soil by loosening it and adding compost. Sow seeds about ¼ inch deep and 6 inches apart. Since arugula bolts in the heat, direct sowing is best done in the cooler parts of the growing season.

Arugula needs consistent moisture to thrive, but it doesn't like soggy soil. In our dry Mountain West climate, regular watering is essential, especially during the warmer months. Aim to keep the soil consistently moist to the touch.

During the spring and fall, when temperatures are cooler, you may only need to water once or twice a week, depending on rainfall. In the heat of summer, you might need to water every other day or even daily, especially if the plants are in full sun. Use the finger test: 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.

Water at the base of the plants to avoid wetting the leaves, which can increase the risk of fungal diseases, though our low humidity helps mitigate this. Wilting leaves are a sign of underwatering, while yellowing leaves can indicate overwatering. A light layer of mulch, such as straw or wood chips, can help retain moisture and keep the soil cool.

You can start harvesting arugula about 40 days after planting, which means you could be enjoying fresh greens from mid May through early October. The best time to harvest is when the leaves are young and tender, about 2-3 inches long, for a milder flavor. Larger leaves will have a more pronounced peppery taste.

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 arugula throughout the season. As the first frost approaches in early October, harvest any remaining leaves to enjoy before the season ends.

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. Small dark beetles that jump when disturbed.
• What causes it: Small jumping beetles that feed on leaves, especially of young seedlings. They love our dry conditions.
• How to fix/prevent it: Use row covers to protect seedlings. Delay planting until plants are larger. You can also try kaolin clay or neem oil.

Bolting in Heat

• What it looks like: Arugula sends up a flower stalk, and the leaves become tough and bitter.
• What causes it: Extended warm temperatures. Our intense sun can cause the soil to heat up quickly.
• How to fix/prevent it: Time plantings for cool weather. Choose bolt-resistant varieties. Provide shade during warm spells. Mulch to keep the soil cool.

Aphids

• What it looks like: Clusters of tiny insects (green, black, or white) on stems and leaf undersides. Sticky honeydew residue.
• What causes it: Rapid-reproducing sap-sucking insects.
• How to fix/prevent it: Strong water spray knocks them off. Encourage natural predators like ladybugs. Use insecticidal soap or neem oil.

Downy Mildew

• What it looks like: Yellow patches on leaf tops with fuzzy gray-purple growth on undersides.
• What causes it: Oomycete pathogen that spreads in cool, humid conditions.
• How to fix/prevent it: Remove affected leaves immediately. Improve air circulation. Water at the base, never overhead.

Mountain West Specific Challenges: Our moderate-at-altitude heat, low humidity, and dry conditions can make arugula susceptible to bolting and flea beetles. Consistent watering and careful monitoring are key to success. The intense UV light also means shading during the hottest part of the day can be beneficial.

Arugula benefits from companion planting. Lettuce and spinach are good companions because they share similar growing requirements and can provide shade for each other. Carrots and beets help loosen the soil, making it easier for arugula roots to grow. Onions repel some pests that might bother arugula. Avoid planting arugula near strawberries, as they can attract pests that will also attack your arugula.