Arugula in Zone 4A — Midwest

Arugula, with its peppery bite, is a fantastic addition to any Midwest garden. It thrives in our fertile soil and provides fresh greens for salads and more, even when those summer heat spells hit. Plus, the satisfaction of harvesting your own spicy leaves is hard to beat.

Our Midwest weather can be unpredictable, with variable springs and occasional summer heat waves, but with some careful timing, you can enjoy a steady supply of arugula throughout our 128-day growing season. We just need to be smart about when we plant.

Starting arugula indoors is definitely an option, but honestly, it's usually not necessary in the Midwest. It's so quick to germinate and grow, direct sowing is often the easier route. However, if you're eager to get a very early start, you can start seeds indoors early to late April, about 3 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 soak it up. Provide warmth and plenty of light; a grow light is ideal, especially given our moderate-to-late spring starts here.

Once the danger of hard frost has passed, typically early May through mid June, you can transplant your arugula seedlings outdoors. Before transplanting, harden them off by gradually exposing them to outdoor conditions for about a week. This helps them adjust to the Midwest elements.

Space the plants about 6 inches apart in a sunny spot with well-drained soil. Be mindful of unexpected late frosts that sometimes sneak up on us in early May. If one is predicted, cover your transplants with a frost blanket or even an overturned bucket for the night.

Direct sowing arugula is the most common and often the best method in the Midwest. You can sow seeds mid April through late July for a continuous harvest. Arugula germinates quickly, and you'll be enjoying fresh leaves in no time.

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 just a few days. Keep in mind that arugula tends to bolt (go to seed) in hot weather, so planting in cooler periods is key.

Arugula needs consistent moisture, especially here in the Midwest, where we can experience both periods of adequate rainfall and summer heat spells. While we often get 30-40 inches of rain, it's not always evenly distributed. Maintaining consistent moisture is vital for preventing bolting and ensuring the best flavor.

Check the soil moisture regularly using the "finger test" – stick your finger about 2 inches deep into the soil. If it feels dry, it's time to water. Aim for about 1 inch of water per week, either from rainfall or irrigation. It's best to water at the base of the plants rather than overhead, especially given our moderate-to-humid conditions, to minimize the risk of fungal diseases.

Signs of underwatering include wilting leaves and a very strong, almost bitter flavor. Overwatering, on the other hand, can lead to yellowing leaves and root rot. A layer of mulch, like straw or shredded leaves, can help retain soil moisture and regulate soil temperature, which is especially helpful during our summer heat.

You can expect your first arugula harvest about 40 days after planting, which means from late May through late September depending on when you sowed. Harvest young leaves when they are about 2-3 inches long for a milder flavor. Larger leaves will have a more pronounced peppery taste.

To harvest, simply snip off the leaves with scissors or a knife, leaving the central growing point intact. This encourages continued production. Harvest regularly to prevent the plant from bolting. As our first frost approaches in mid- September, harvest all remaining leaves, even the smaller ones, to make the most of your crop. You can even cover plants with a frost blanket for a short while to extend the harvest a bit.

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

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: Flea beetles are small jumping beetles that feed on the leaves. They are most damaging to small, young plants in spring.
• How to fix/prevent it: Use row covers to protect seedlings during their vulnerable stage. You can also delay planting until the plants are larger and more resilient. Coating plants with kaolin clay can deter the beetles. Neem oil spray can also help. Consider interplanting with basil or catnip, which are known to repel flea beetles.

Bolting in Heat

• What it looks like: The plant sends up a flower stalk, and the leaves become tough and bitter.
• What causes it: Arugula is a cool-season crop, and it bolts when temperatures rise. Summer heat spells are common in the Midwest, which can trigger bolting.
• How to fix/prevent it: Time your plantings for cooler weather in spring and fall. Choose bolt-resistant varieties if possible. Provide shade during warm spells with shade cloth. Mulch around the plants to keep the soil cool. Harvest frequently to encourage leaf production before bolting progresses.

Aphids

• What it looks like: Clusters of tiny, soft-bodied insects (green, black, or white) on stems and the undersides of leaves. You might also notice a sticky honeydew residue and curled or distorted new growth.
• What causes it: Aphids are sap-sucking insects that reproduce rapidly, especially in warm weather.
• How to fix/prevent it: Knock aphids off plants with a strong water spray. Encourage natural predators like ladybugs and lacewings. Use insecticidal soap for heavy infestations. Neem oil is also effective. Avoid excess nitrogen fertilizer, as it attracts aphids.

Downy Mildew

• What it looks like: Yellow patches on the tops of leaves with fuzzy gray-purple growth on the undersides. Leaves brown and die from the bottom up.
• What causes it: Downy mildew is caused by a pathogen that spreads in cool, humid conditions via wind-carried spores.
• How to fix/prevent it: Remove affected leaves immediately. Improve air circulation around the plants. Water at the base, avoiding overhead watering. Copper-based fungicides can be used for prevention. Plant resistant varieties if available.

Midwest Specific Challenges: Our moderate-to-hot summers and moderate-to-humid conditions can create a perfect storm for bolting and fungal diseases like downy mildew in arugula. Be diligent about watering, provide shade during heat spells, and ensure good air circulation to keep your arugula healthy and productive.

Arugula benefits from companion planting. Lettuce and spinach make good companions because they share similar growing requirements and don't compete for resources. Carrots and beets are also beneficial, as they help loosen the soil, making it easier for arugula roots to grow. Onions can help deter pests like aphids.

Avoid planting arugula near strawberries. Strawberries and arugula are susceptible to some of the same fungal diseases, which can increase the risk of infection, especially in our humid Midwest summers.