Arugula in Zone 7A — 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, the satisfaction of harvesting fresh greens just weeks after planting is hard to beat, especially with our intense sunlight helping them grow quickly.

While our high altitude, intense sun, and alkaline soil present challenges, Arugula's short 40-day maturity makes it a perfect fit for our 173-day growing season. Careful timing and attention to watering will ensure a bountiful harvest.

Starting Arugula indoors isn't essential, but it can give you a head start, especially with our late springs. If you want to get a jump on the season, start seeds indoors from early to late March, about three weeks before you plan to transplant.

Use seed trays with a good seed-starting mix and keep them in a warm location with plenty of light – a south-facing window or under grow lights works well. Remember to water from the bottom to prevent damping off. Starting indoors can be helpful if we have a particularly cold spring, but direct sowing is often just as effective.

Transplant your Arugula seedlings outdoors from early April through mid May, after the danger of hard frost has passed. Before transplanting, harden them off by gradually exposing them to outdoor conditions for about a week.

Space the seedlings about 6 inches apart in well-drained soil. Keep an eye on the weather forecast, as we can still get unexpected cold snaps in April and May. If frost is predicted, cover the seedlings with row covers or blankets.

Direct sowing is the most common and easiest way to grow Arugula in our region. You can sow seeds directly into the garden from late March through mid August.

Prepare the soil by loosening it and removing any rocks or debris. Arugula prefers soil temperatures between 45°F and 65°F for optimal germination. Sow seeds about ¼ inch deep and 6 inches apart. Keep the soil consistently moist until the seedlings emerge, which should take about a week. Direct sowing is great because it avoids transplant shock, but you'll need to watch out for flea beetles early on.

Arugula needs consistent moisture to thrive, but it doesn't like to be waterlogged. In our dry Mountain West climate, especially with our low humidity and limited rainfall, watering is critical.

During the spring and fall, when temperatures are cooler, water deeply about once a week, providing about 1 inch of water. In the summer, especially when daytime highs reach around 85°F, you may need to water every other day or even daily. 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 lead to fungal diseases. Overwatering can cause yellowing leaves and root rot, while underwatering can lead to bolting and a more intense, sometimes bitter, flavor. A light layer of mulch, like straw or wood chips, can help retain moisture and keep the soil cool.

You can expect your first Arugula harvest from early May through mid October, about 40 days after planting. Harvest young leaves when they 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. As the first frost approaches in early October, harvest any remaining leaves or cover the plants with a row cover to extend the season a bit 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 the leaves, especially on young seedlings. You might see small, dark beetles that jump when disturbed.
• What causes it: These small jumping beetles feed on the leaves, and they're most damaging to small, young plants. Our intense sun can stress seedlings, making them more vulnerable.
• How to fix/prevent it: Protect seedlings with row covers during their vulnerable stage. Delay planting until plants are larger and stronger. You can also try coating the leaves with kaolin clay or spraying with neem oil. Interplanting with basil or catnip can help deter them.

Bolting in Heat

• What it looks like: The Arugula sends up a flower stalk, and the leaves become tough and bitter.
• What causes it: As a cool-season crop, Arugula bolts when temperatures rise. This is especially common during our brief but intense summer heat.
• How to fix/prevent it: Time your plantings for cool weather in spring and fall. Choose bolt-resistant varieties. Provide shade during warm spells with shade cloth. Mulch to keep the soil cool. Harvest leaves frequently to encourage continued leaf production before bolting progresses.

Aphids

• What it looks like: Clusters of tiny soft-bodied insects (green, black, or white) on stems and leaf undersides. You might also see a sticky honeydew residue and curled or distorted new growth.
• What causes it: These sap-sucking insects reproduce rapidly, especially in warm weather.
• How to fix/prevent it: Knock them off with a strong water spray. Encourage beneficial insects like ladybugs and lacewings. Use insecticidal soap for heavy infestations. Neem oil also works well. Avoid excess nitrogen fertilizer, which can attract them.

Downy Mildew

• What it looks like: Yellow patches on the tops of leaves with fuzzy gray-purple growth on the undersides. Leaves will brown and die from the bottom up.
• What causes it: This is caused by an oomycete pathogen that spreads in cool, humid conditions.
• How to fix/prevent it: Remove affected leaves immediately. Improve air circulation by spacing plants properly. Water at the base of the plants, never overhead. Copper-based fungicides can be used for prevention.

Mountain West Specific Challenges: Our moderate-at-altitude heat and low humidity can be a double-edged sword for Arugula. The intense sun can stress plants, making them more susceptible to bolting and flea beetles. The low humidity helps prevent fungal diseases like downy mildew, but it also means we need to be extra vigilant about watering. Consistent moisture management is key to success.

Good companions for Arugula include lettuce and spinach, as they share similar growing requirements and can help create a beneficial microclimate. Carrots and beets are also good choices, 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 target the Arugula.