Mustard Greens in Zone 9A — Desert Southwest

Mustard greens bring a peppery zing to your table, and in our Desert Southwest climate, they're a rewarding crop for both spring and fall harvests. Their fast growth and tolerance for light frost make them a fantastic addition to your garden, offering fresh greens when other plants are struggling in the extreme heat.

Desert gardening definitely has its challenges, but with careful timing, you can easily avoid the worst of the summer sunscald and keep your mustard greens happy. Our long, 298-day growing season gives you two solid windows to enjoy this tasty crop.

Starting mustard greens indoors isn't essential in our climate, but it can give you a head start, especially for the early spring crop. Sow seeds indoors from early to late January, about three weeks before you plan to transplant. This is useful if an unexpected cold snap comes through.

Use seed trays or small pots filled with well-draining potting mix. Keep the soil consistently moist by bottom watering to avoid damping off. Provide warmth and plenty of light, and remember that spring starts early here!

Transplant your mustard green seedlings outdoors from early February through mid March. Before transplanting, harden them off by gradually exposing them to outdoor conditions for about a week. This helps them adjust to the intense Desert Southwest sun.

Space the seedlings 6-12 inches apart in well-drained soil. Keep an eye on the weather forecast—late frosts are rare, but possible, and young transplants may need protection if temperatures dip unexpectedly.

Direct sowing is a great option for mustard greens in our region, as you can sow seeds from mid January through mid October. The key is to avoid the peak of the summer heat. Soil temperatures between 60°F and 70°F are ideal for germination.

Prepare the soil by loosening it and adding compost to improve drainage. Sow seeds 1/4 to 1/2 inch deep, spacing them 6-12 inches apart, or sow them closer together and thin later. Keep the soil consistently moist until the seedlings emerge.

Watering is crucial for mustard greens, especially with our extreme heat and arid conditions. Aim to keep the soil consistently moist, but not waterlogged. Drought stress can make the leaves spicier and trigger bolting, which is something we want to avoid.

During the cooler spring and fall, water deeply once or twice a week, providing about 1 inch of water each time. In the hotter months or during monsoon moisture, you may need to water more frequently—use the finger test (checking the soil moisture about 2 inches deep) to guide you. Water at the base of the plants to avoid wetting the leaves, which can minimize the risk of fungal issues given our low humidity.

Signs of underwatering include wilting leaves and slow growth. Overwatering can lead to yellowing leaves and root rot. A layer of organic mulch, like shredded leaves or straw, can help retain moisture and keep the soil cool.

You can expect your first harvest of mustard greens around early March through mid December, about 45 days after planting. Young leaves have a milder flavor, while larger leaves become spicier as they mature. It's best to harvest before the plant starts to flower, as bolting will make the leaves bitter.

To harvest, simply snip off the outer leaves with scissors or a knife, leaving the inner leaves to continue growing. This allows for continuous harvesting throughout the season. As the first frost approaches in early December, harvest any remaining leaves to prevent them from being damaged.

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 the leaves. You'll see small, dark beetles that jump when disturbed.
• What causes it: These small jumping beetles feed on the leaves, and they can be especially damaging to young seedlings.
• 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 resistant. Kaolin clay coating and neem oil spray can help. Interplant with basil or catnip to deter them.

Aphids

• What it looks like: Clusters of tiny, soft-bodied insects (green, black, or white) on the stems and leaf undersides. You might also see 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.
• How to fix/prevent it: Knock them off with a strong spray of water. Encourage natural predators like ladybugs and lacewings. Use insecticidal soap for heavy infestations. Neem oil also works. Avoid excess nitrogen fertilizer, as it attracts them.

Cabbage Worms

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

Bolting in Heat

• What it looks like: The plant sends up a flower stalk, and the leaves become tough and bitter. Harvest quality declines.
• What causes it: Extended warm temperatures above the plant's comfort zone. Mustard greens bolt when temperatures consistently exceed 80°F.
• How to fix/prevent it: Time your plantings for the cooler spring and fall weather. 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: Our extreme heat and arid humidity make mustard greens more susceptible to bolting and drought stress. Monitor soil moisture closely and provide shade during the hottest parts of the day to keep your plants happy and productive. The monsoon rainfall can also increase the risk of fungal diseases, so ensure good air circulation around your plants.

Good companions for mustard greens include onions and garlic, as their pungent scent can deter pests. Beets are also beneficial, as they don't compete for the same nutrients. Dill attracts beneficial insects that prey on aphids and cabbage worms. Lettuce can provide ground cover, helping to retain moisture in our dry climate.

Avoid planting mustard greens near strawberries or tomatoes. Strawberries and mustard greens compete for similar nutrients. Tomatoes can attract some of the same pests that bother mustard greens, increasing the risk of infestation.