Arugula in Zone 5B — Great Plains

Arugula, with its peppery bite, is a fantastic addition to any Great Plains garden. It’s quick to mature, so you can get multiple harvests even with our shorter growing season, and it adds a unique flavor to salads, sandwiches, and even pizzas. Plus, it thrives in the cool weather of spring and fall, making it a great option when other greens struggle with the summer heat.

Our region definitely throws some curveballs with extreme temperature swings and the occasional hail risk. But with a 178-day growing season and a bit of planning, you can easily grow a thriving patch of arugula. Timing your plantings right is key to avoiding the worst of the summer heat and extending your harvest well into the fall.

Starting arugula indoors is an option, but honestly, it's so fast-growing that direct sowing is usually the way to go. If you want a super early start, though, aim to sow seeds indoors in 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 spot with plenty of light – a sunny windowsill or under grow lights works well. Bottom watering helps prevent damping-off, which can be an issue with seedlings. Remember, spring weather in the Plains is variable, so indoor starting gives you a head start if we have a late cold snap.

Transplanting arugula outdoors is best done from early April through mid May. Before you move your seedlings out, harden them off for about a week by gradually exposing them to outdoor conditions. This helps them adjust to the wind and temperature swings common in our region.

Plant them about 6 inches apart in well-drained soil. Keep an eye on the forecast – a late frost can still happen, so be ready to cover your seedlings if needed.

Direct sowing arugula is incredibly easy and often the preferred method. Sow seeds late March through late August for successive harvests. Arugula germinates best in cool soil, so spring and fall plantings are ideal.

Prepare your 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. The downside is that it bolts in heat, so pay attention to the calendar.

Arugula needs consistent moisture to thrive, but overwatering can be just as detrimental as underwatering, especially with our variable rainfall patterns. Aim to keep the soil consistently moist, but not soggy. During the hotter months, this might mean watering every other day, while in cooler weather, you can stretch it out to every few days.

The "finger test" is your best friend – stick your finger about 2 inches deep into the soil. If it feels dry, it's time to water. A good rule of thumb is to provide about 1 inch of water per week, either through rainfall or irrigation. In our low-to-moderate humidity, watering at the base of the plants is usually fine, but avoid overhead watering to prevent fungal diseases.

Signs of underwatering include wilting leaves and a strong, bitter taste. Overwatering can lead to yellowing leaves and root rot. A light layer of mulch, like straw or shredded leaves, can help retain moisture and keep the soil cool, which is especially helpful during the summer heat.

You can expect your first arugula harvest starting early May and extending through late October. Arugula is ready to harvest about 40 days after planting. Look for leaves that are 2-3 inches long for a milder flavor, or let them grow larger for a more peppery taste.

Harvest by snipping off the outer leaves, leaving the inner ones to continue growing. This encourages continued production throughout the season. To extend your harvest as the first frost approaches in mid- October, consider covering your plants with a row cover or bringing them indoors in containers to protect them from the cold.

Here are some common problems you might encounter with arugula in the Great Plains:

Flea Beetles

• What it looks like: Tiny round holes (shot-hole pattern) in the leaves, especially on young seedlings. You might also see small, dark beetles jumping around when disturbed.
• What causes it: These small jumping beetles feed on the leaves. They're most damaging to small, young plants.
• How to fix/prevent it: Row covers are essential to protect seedlings during their vulnerable stage. You can also delay planting until the plants are larger and more resilient. Coating the leaves with kaolin clay can deter them, and neem oil spray can also help. Try interplanting with basil or catnip, as they seem to dislike those. Healthy, vigorous plants often outgrow the damage.

Bolting in Heat

• What it looks like: The plant sends up a flower stalk, and the leaves become tough and bitter. Overall harvest quality declines.
• What causes it: Arugula is a cool-season crop, and it bolts when temperatures consistently rise above 80°F.
• How to fix/prevent it: Time your plantings for cool weather in spring and fall. Choose bolt-resistant varieties if you can find them. Provide shade during warm spells with shade cloth or by planting near taller crops. Mulch 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 leaf undersides. 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: A strong spray of water can knock them off the plants. Encourage natural predators like ladybugs and lacewings. Insecticidal soap can be used for heavy infestations, and neem oil works systemically. Avoid excess nitrogen fertilizer, as it attracts them.

Downy Mildew

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

Great Plains Specific Challenges: The hot summers and variable rainfall in the Great Plains can make it challenging to keep arugula consistently moist and prevent bolting. The wind can also dry out the soil quickly, so mulching is key. Watch out for those extreme temperature swings, too, which can stress the plants and make them more susceptible to pests and diseases.

Arugula benefits from companion planting. Lettuce and spinach are good companions because they have similar growing requirements and don't compete for resources. Carrot and beet also work well, as they help loosen the soil, which arugula appreciates.

Onions can help deter pests like aphids. Avoid planting arugula near strawberries, as they can attract pests that also affect arugula. By choosing the right companions, you can create a healthier and more productive garden.