Arugula in Zone 3A — Great Plains

Arugula is a fantastic addition to any Great Plains garden. Its peppery bite adds zest to salads and sandwiches, and it's surprisingly versatile in cooked dishes too. Plus, few things beat the satisfaction of harvesting your own greens just minutes before they hit the plate, especially after a long winter.

Our extreme weather can be a challenge, but arugula's quick growth cycle makes it a winner. With a 108-day growing season, you can easily squeeze in multiple plantings of this semi-hardy green. Timing is key, and with a little planning, you'll be enjoying fresh arugula all season long.

Starting arugula indoors is definitely possible, but honestly, it's often not necessary for us here on the Plains. Arugula sprouts so quickly, direct sowing is usually the way to go. But if you want a head start, or if we're dealing with a particularly variable spring, starting seeds indoors from mid-April through early May (about 3 weeks before transplanting) can work well.

Use seed trays or small pots filled with seed-starting mix. Keep them warm (around 70°F) and provide plenty of light, either from a grow light or a sunny south-facing window. Bottom watering is a great way to keep the soil consistently moist without damping off. Just set the tray in a shallow dish of water and let the soil soak it up from the bottom.

Transplanting arugula is straightforward. Aim to transplant seedlings outdoors from mid-May through late June, once the danger of a hard frost has passed. Before planting directly into your garden, be sure to harden off your seedlings by gradually exposing them to outdoor conditions for about a week.

Space the plants about 6 inches apart. Keep an eye on the weather forecast – a late-season frost or a sudden hailstorm can still happen! Provide some temporary wind protection to help the young plants establish.

Direct sowing arugula is the easiest way to grow it in the Great Plains. You can start sowing seeds outdoors from late April through mid-July, giving you a long window for multiple harvests. Arugula is fast-growing, but it also bolts quickly in the heat, so planting in cooler weather is crucial.

Prepare your soil by loosening it and removing any large clumps. Arugula prefers well-drained soil with a pH between 6.0 and 7.0. Sow seeds about ¼ inch deep and 6 inches apart. Keep the soil consistently moist until the seeds germinate, which should take about a week.

Arugula needs consistent moisture to thrive, but it's important to avoid overwatering, especially with our variable rainfall. Aim to keep the soil consistently moist, but not soggy. Letting the soil dry out too much will intensify the peppery flavor, which some people like, but it can also stress the plant and encourage bolting.

During the cooler spring and fall months, you might only need to water once or twice a week, depending on rainfall. In the heat of summer, especially when temperatures are hitting the low 90s, you'll likely need to water every day or every other day. Do the finger test: stick your finger about 2 inches into the soil. If it feels dry, it's time to water. Aim for about an inch of water per week, either from rainfall or irrigation.

Water at the base of the plants to avoid wetting the foliage, which can encourage fungal diseases, though low-to-moderate humidity means we don't usually have big problems with that here. If the leaves are wilting or turning yellow, you're likely overwatering. If the leaves are dry and brittle, you're likely underwatering. A layer of mulch, like straw or wood chips, can help retain moisture and keep the soil cool, which is especially helpful during hot spells.

You can expect your first arugula harvest about 40 days after planting, so from early June through mid-September. Start harvesting when the leaves are about 2-3 inches long for a milder flavor, or wait until they're larger for a more peppery taste. The key is to harvest before the plant starts to flower.

To harvest, simply snip off the outer leaves with scissors or garden shears, leaving the inner leaves to continue growing. This cut-and-come-again method will give you a continuous harvest throughout the season. As the first frost approaches in early September, harvest any remaining leaves. Arugula can tolerate a light frost, but a hard freeze will kill it.

Arugula is generally easy to grow, but there are a few common problems to watch out for.

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 when disturbed.
• What causes it: Flea beetles are small jumping beetles that feed on the leaves of brassicas and other crops. 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 better able to withstand the damage. Kaolin clay coating can act as a physical barrier. Neem oil spray can also help. Interplanting with basil or catnip might deter them.

Bolting in Heat

• What it looks like: The plant sends up a flower stalk, and the leaves become tough and bitter. Harvest quality declines rapidly.
• What causes it: Arugula is a cool-season crop that bolts when temperatures rise. This is a real concern with our Plains heat.
• How to fix/prevent it: Time your plantings for cooler weather in spring and fall. Choose bolt-resistant varieties if you can find them. Provide shade during warm spells with shade cloth. Mulch to keep the soil cool. Harvest 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. 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. Encourage ladybugs and lacewings, which are natural predators. Insecticidal soap can be used for heavy infestations. Neem oil also works. Avoid excess nitrogen fertilizer, as it attracts them.

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 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, never overhead. Copper-based fungicides can be used for prevention.

Great Plains Specific Challenges: Our hot summers, low-to-moderate humidity, and variable rainfall can all impact arugula. The heat encourages bolting, so timing your plantings is crucial. While humidity is generally low, periods of high humidity can increase the risk of downy mildew. And our variable rainfall means you need to be vigilant about watering, ensuring the plants get enough moisture without being overwatered.

Arugula benefits from companion planting. Lettuce and spinach are good companions because they share similar growing requirements and can provide shade for each other, helping to keep the soil cool. Carrots and beets are also good companions because they don't compete for the same nutrients and can help to loosen the soil. Onions can help to deter pests like aphids.

Avoid planting arugula near strawberries. Strawberries are susceptible to verticillium wilt, which can also affect arugula.