Mustard Greens in Zone 9B — Desert Southwest

Mustard Greens deliver a spicy kick to your meals, and they're incredibly versatile. Here in the Desert Southwest, they're a fantastic addition to your garden because you can harvest them throughout our mild winters and shoulder seasons, adding fresh greens to your table when other crops are taking a break.

Our extreme heat can be a challenge, but with careful timing and attention to watering, you can enjoy a bountiful harvest of Mustard Greens. Our long 313-day growing season gives you two opportunities to grow this crop successfully: one in the spring and another in the fall.

Starting Mustard Greens indoors is an option, especially if you want a head start on the spring growing season. Begin in late December through mid January, about three weeks before you plan to transplant. Use seed trays with a good seed-starting mix, and keep them warm and under grow lights until they sprout.

Bottom watering is a great way to keep the soil consistently moist without disturbing the delicate seedlings. Given our very-early spring character, indoor starting can help you get a jump on the season.

Transplant your Mustard Greens seedlings outdoors in late January through early March. Before transplanting, harden them off for about a week by gradually exposing them to outdoor conditions. This helps them adjust to the Desert Southwest's intense sunlight and temperature fluctuations.

Space the seedlings 6-12 inches apart to allow for proper air circulation and growth. Keep a close eye on the weather forecast and protect young transplants from any unexpected late frosts or strong winds.

Direct sowing Mustard Greens is a straightforward method, and it works well in our climate. Sow seeds directly into the garden from early January through mid October. Ensure the soil is well-prepared and has warmed up a bit, ideally around 60-70°F.

Plant the seeds about ¼ inch deep and space them 6-12 inches apart. Direct sowing eliminates the need for transplanting, but you'll need to be diligent about thinning seedlings to the correct spacing as they emerge.

Watering is critical for Mustard Greens in our arid Desert Southwest climate. Aim to keep the soil consistently moist, but not waterlogged. Drought stress will make the leaves spicier and can cause the plant to bolt prematurely.

During the cooler spring and fall months, you'll likely need to water 2-3 times per week, providing about 1 inch of water each time. During the monsoon season, monitor rainfall and adjust your watering schedule accordingly. In the extreme heat of summer, you might need to water daily, especially if the plants are in full sun.

Use the "finger test" to check the soil moisture about 2 inches deep. If it feels dry, it's time to water. Water at the base of the plants to avoid wetting the leaves, which can increase the risk of fungal diseases in our arid climate. Signs of underwatering include wilting leaves, while overwatering can lead to yellowing leaves and root rot. Mulching around the plants with organic matter like compost can help retain moisture and regulate soil temperature.

You can expect your first harvest of Mustard Greens in late February through late December, about 45 days after planting. The leaves are ready to harvest when they are a few inches long. Young leaves will have a milder flavor, while larger leaves will be spicier.

Harvest the outer leaves as needed, leaving the inner leaves to continue growing. This encourages continuous production throughout the growing season. Be sure to harvest before the plant starts to flower, as bolting will make the leaves bitter.

As the first frost approaches in mid- December, harvest any remaining leaves to enjoy before the cold weather sets in. Mustard Greens are semi-hardy, but a hard freeze can damage the leaves.

Here are some common problems you might encounter with Mustard Greens in the Desert Southwest:

Flea Beetles

• What it looks like: Tiny round holes (shot-hole pattern) in 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 thrive in our warm, dry conditions. They are most damaging to small, young plants.
• How to fix/prevent it: Use row covers to protect seedlings during their vulnerable stage. Delay planting until plants are larger and more resilient. You can also try spraying with kaolin clay or neem oil. Interplanting with basil or catnip may help deter them.

Aphids

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

Cabbage Worms

• What it looks like: Smooth green caterpillars on the leaves, with irregular holes chewed in them. You might also see dark green droppings and white butterflies hovering around your plants.
• What causes it: These are the larvae of white cabbage butterflies. They can have multiple generations per season in our warm climate.
• How to fix/prevent it: Bt spray is very effective. Use floating row covers to prevent the butterflies from laying eggs. Handpick caterpillars when you see them. Interplant with aromatic herbs like thyme or sage to deter the butterflies. Encourage parasitic wasps, which prey on the caterpillars.

Bolting in Heat

• What it looks like: The plant sends up a flower stalk. The leaves become tough and bitter, and the harvest quality declines.
• What causes it: This happens when temperatures rise and the plant thinks it needs to reproduce quickly. Brassicas bolt when days consistently exceed 80°F.
• How to fix/prevent it: Time your plantings for the cooler parts of the year (spring and fall). Choose bolt-resistant varieties. Provide shade during warm spells with shade cloth. Mulch to keep the soil cool. Harvest before bolting progresses too far.

Desert Southwest Specific Challenges: The extreme heat and intense sunlight in our region can exacerbate these problems. Flea beetles and aphids thrive in dry conditions, and bolting is a constant threat during the warmer months. Water scarcity means you need to be vigilant about watering to prevent drought stress, which can weaken the plants and make them more susceptible to pests and diseases. However, our low humidity can help reduce the risk of fungal diseases. Monsoon moisture can be a blessing, but also create conditions for pests.

Mustard Greens benefit from companion planting. Onions and garlic are good companions because their pungent aroma deters pests like aphids and flea beetles. Beets improve soil health, which benefits mustard greens. Dill attracts beneficial insects like ladybugs and lacewings, which prey on aphids. Lettuce provides ground cover, helping to keep the soil cool and moist.

Avoid planting Mustard Greens near strawberries and tomatoes. Strawberries are susceptible to verticillium wilt, which can also affect Mustard Greens. Tomatoes compete for the same nutrients in the soil, which can stunt the growth of both plants.