Arugula in Zone 3A — Mountain West

Arugula is a fantastic addition to any Mountain West garden. Its peppery bite adds a unique flavor to salads and sandwiches, and it thrives in our cool spring and fall weather. Plus, the satisfaction of harvesting fresh greens just weeks after planting is especially rewarding in our short growing season.

While our high altitude and intense sun can present challenges, arugula's quick maturity makes it a manageable crop even with our 96-day growing season. With careful timing and attention to watering, you can enjoy a continuous harvest from mid-June through September.

Starting arugula indoors is an option, but honestly, it's usually not necessary here in the Mountain West. Because arugula germinates so quickly and tolerates cool weather, direct sowing is often the easier route.

If you want a head start, begin your seeds indoors mid April through mid May, 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 watering from the bottom to avoid disturbing the delicate seedlings. Place the trays in a warm spot with plenty of light – a sunny windowsill or under grow lights will work. Remember, spring can be late in the high country, so be patient!

Transplant your arugula seedlings outdoors mid May through late June, once the danger of hard frost has passed. Before transplanting, harden off the seedlings by gradually exposing them to outdoor conditions for about a week. This helps them adjust to the intense sun and cooler nights.

When transplanting, space the seedlings about 6 inches apart in well-drained soil. Even though the calendar might say it's late spring, be prepared for unexpected cold snaps or even a late-season snow flurry. Row covers can be helpful if the weather turns harsh soon after transplanting.

Direct sowing arugula is the most common and easiest method for Mountain West gardeners. Sow seeds early May through mid July for a continuous harvest. Arugula is fast-growing and does best in the cooler parts of the growing season.

Prepare the soil by loosening it and removing any rocks or debris. Sow seeds about ¼ inch deep and 6 inches apart. Keep the soil consistently moist until the seedlings emerge, usually within a week. The biggest challenge is to keep the soil cool enough, as arugula bolts quickly in hot weather.

Arugula needs consistent moisture to thrive, but it's crucial to avoid overwatering, especially in our alkaline soil. Keep the soil consistently moist, but not soggy. Aim for about 1 inch of water per week, either from rainfall or irrigation.

During the cooler spring and fall months, you may only need to water a couple of times a week. In the heat of summer, especially with our low humidity, you might need to water more frequently. Use the "finger test" – stick your finger about 2 inches into the soil. If it feels dry, it's time to water. Water at the base of the plants to avoid wetting the leaves, which can increase the risk of fungal diseases.

Signs of underwatering include wilting leaves and slow growth. 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, but avoid piling it directly against the stems.

You can expect your first arugula harvest mid June through mid September, about 40 days after planting. The key is to harvest young leaves when they are 2-3 inches long for the mildest flavor. Larger leaves will have a more pronounced peppery taste.

Harvest by snipping off the outer leaves with scissors or a knife, leaving the inner leaves to continue growing. This encourages continued production. To extend your harvest into the fall, consider planting another round of seeds in late summer. As the first frost approaches in early September, you can cover your arugula with a row cover to protect it from the cold and extend the harvest a little longer.

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 also see small dark beetles that jump when disturbed.
• What causes it: Flea beetles are small jumping beetles that feed on the leaves. They are most damaging to small, young plants, and the intense sun can stress the plants, making them more susceptible.
• How to fix/prevent it: Row covers are your best defense to protect seedlings. Delay planting until plants are larger. Kaolin clay coating can also deter them. You can also try interplanting with basil or catnip.

Bolting in Heat

• What it looks like: The arugula sends up a flower stalk, and the leaves become tough and bitter.
• What causes it: Arugula is a cool-season crop and bolts when temperatures rise. Our intense sun and fluctuating temperatures can trigger bolting even if the air temperature doesn't seem that high.
• How to fix/prevent it: Time your plantings for cool weather in spring and fall. Choose bolt-resistant varieties if possible. Provide shade during warm spells with shade cloth. Mulch to keep the soil cool. Harvest frequently to encourage new growth and 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 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. Our dry climate can stress plants, making them more vulnerable to aphid infestations.
• How to fix/prevent it: A strong water spray can knock them off. Encourage ladybugs and lacewings, which are natural predators. Insecticidal soap can be used 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: Downy mildew is a disease that spreads in cool, humid conditions. While our humidity is generally low, cool nights and occasional wet spells can create favorable conditions for downy mildew.
• How to fix/prevent it: Remove affected leaves immediately. Improve air circulation by spacing plants properly. Water at the base, never overhead. Copper-based fungicides can be used for prevention.

Mountain West Specific Challenges: Our moderate-at-altitude heat, low humidity, and dry rainfall present a mixed bag for arugula. The intense sun can increase the risk of bolting and flea beetle damage, but the low humidity helps to reduce the risk of fungal diseases. Consistent watering and careful timing are key to success.

Arugula benefits from companion planting in our Mountain West gardens. Lettuce and spinach make good companions because they share similar growing requirements and help to shade the soil, keeping it cool. Carrots and beets are also beneficial because they loosen the soil, improving drainage. Onions deter pests like aphids. Avoid planting arugula near strawberries, as they can attract slugs that will also feed on the arugula.