Arugula in Zone 6A — Mountain West

Arugula is a fantastic addition to any Mountain West garden. Its peppery bite adds zest to salads, pizzas, and pesto, and it thrives in our region's cool springs and falls. Plus, that intense mountain sun really concentrates its flavor!

Our short growing season (around 153 days) and unpredictable weather can be a challenge, but with careful timing and a little attention, you can enjoy a steady supply of fresh arugula from mid-spring through fall. Don't let those cool nights scare you – arugula loves them!

Starting arugula indoors is definitely an option here, but honestly, it's so quick to germinate and grow, direct sowing is often preferred. However, if you want a super early start, consider starting seeds indoors from 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 them consistently moist by bottom watering – set the tray in a shallow dish of water and let the soil soak it up from the bottom. Provide warmth (a heat mat is helpful) and plenty of light. Remember, spring arrives late here, so give those seedlings a head start indoors to beat the chill.

Transplanting arugula seedlings outdoors can begin mid-April through late 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. Start with an hour or two of shade, increasing the time each day.

When transplanting, space the seedlings about 6 inches apart. Keep an eye on the weather forecast – a late frost can still happen, even in May. If frost is predicted, cover your seedlings with row covers or blankets.

Direct sowing arugula is the easiest way to get a continuous harvest. Sow seeds directly into the garden early April through early August. Arugula is fast-growing and easy to direct sow, but it bolts in the heat, so planting in cool weather is key.

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 germination, which usually takes about a week. For a continuous supply, sow a new batch of seeds every few weeks.

Arugula needs consistent moisture to thrive, but avoid soggy soil. With our dry climate and low humidity, watering correctly is key to success.

During the cooler spring and fall months, you'll likely need to water deeply about once or twice a week, depending on rainfall. In the heat of summer, increase watering to every other day, or even daily if the soil dries out quickly. The "finger test" is your best guide – stick your finger into the soil about 2 inches deep. 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 encourage fungal diseases. Although, with our low humidity, this isn't as much of a concern as in other regions. Signs of underwatering include wilting leaves and a strong, bitter flavor. Overwatering can lead to yellowing leaves and root rot. Mulching around the plants with straw or wood chips helps retain moisture and keep the soil cool.

You can expect your first arugula harvest about 40 days after planting, usually from mid-May through early October. Start harvesting when the leaves are 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 a knife, leaving the inner leaves to continue growing. This cut-and-come-again method will provide you with a continuous harvest throughout the season. Keep harvesting regularly to prevent the plants from bolting (going to seed).

As the first frost approaches in early October, harvest any remaining leaves. You can also cover the plants with a row cover to extend the harvest for a few more weeks.

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. You might see small dark beetles that jump when disturbed.
• What causes it: Small jumping beetles that feed on leaves, especially on young seedlings. They thrive in dry conditions.
• How to fix/prevent it: Use row covers to protect seedlings. Delay planting until plants are larger. Kaolin clay coating can deter them. Neem oil spray also works. Interplant with basil or catnip. Healthy, vigorous plants outgrow the damage.

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 days consistently exceed 80°F. Our intense sun can exacerbate this.
• How to fix/prevent it: Time plantings for cool weather (spring/fall). Choose bolt-resistant varieties. Provide shade during warm spells with shade cloth. Mulch to keep soil cool. Harvest frequently to encourage leaf production before 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: Rapid-reproducing sap-sucking insects. Populations explode in warm weather.
• How to fix/prevent it: Strong water spray knocks them off. Encourage ladybugs and lacewings (natural predators). Insecticidal soap for heavy infestations. Neem oil works systemically. 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 can help prevent it. Plant resistant varieties where available.

Mountain West Specific Challenges: Our moderate-at-altitude heat and low humidity can actually be beneficial for arugula, reducing the risk of fungal diseases like downy mildew. However, the intense sun can quickly cause bolting, so providing shade is crucial during the hottest part of the summer. Hail can also shred the leaves, so consider using row covers for protection.

Arugula benefits from companion planting. Lettuce and spinach make good neighbors, as they have similar growing requirements and help to shade the soil, keeping it cool. Carrots and beets also work well, as they don't compete for the same nutrients. Onions can help deter pests. Avoid planting arugula near strawberries, as they can attract pests that will also attack your arugula.