Mustard Greens in Zone 7B — Desert Southwest

Mustard greens are a fantastic addition to your Desert Southwest garden, offering a spicy kick to salads and cooked dishes. They're incredibly versatile, thriving in our cooler seasons and providing a welcome burst of fresh flavor. Harvesting your own mustard greens, even just a handful at a time, is incredibly satisfying.

While our region presents challenges like extreme heat and alkaline soil, the relatively short growing season of mustard greens makes them entirely manageable. With careful timing, you can enjoy multiple harvests during our 245-day growing season. You can take advantage of our mild winters and long fall season.

Starting mustard greens indoors is an option, but honestly, direct sowing is so easy, it's usually the way to go here. If you want a head start, especially for an early spring crop, start seeds indoors from early to late February, about three weeks before you plan to transplant.

Use seed trays or small pots with good drainage, and keep them in a warm spot with plenty of light – a sunny windowsill or under grow lights works well. Bottom watering is ideal to keep the soil consistently moist without disturbing the seedlings. Remember, we're in a very-early spring region, so indoor starts help you jump ahead.

Transplant your mustard green seedlings outdoors from early March through mid April, after they've developed a few sets of true leaves. Before planting, harden them off by gradually exposing them to outdoor conditions for about a week. This helps them adjust to the intense Desert Southwest sun and temperature swings.

Space your seedlings 6-12 inches apart in well-drained soil. Keep an eye on the weather forecast; a late frost is always possible, so be ready to cover your seedlings if needed.

Direct sowing mustard greens is the simplest method, and it works well for both spring and fall crops. Sow seeds from mid February through mid September, whenever the soil temperature is consistently above 45°F. Prepare the soil by loosening it and adding compost.

Plant seeds about ¼ inch deep, spacing them 6-12 inches apart, or sow them closer and thin later. Keep the soil consistently moist until germination, which usually takes about a week.

Watering is absolutely critical for mustard greens in our arid Desert Southwest climate. Aim to keep the soil consistently moist, but not waterlogged, as drought stress can significantly increase the spiciness of the leaves and trigger premature bolting. Use the "finger test" – if the top two inches of soil feel dry, it's time to water.

During the spring and fall growing seasons, when temperatures are milder, you'll likely need to water deeply about 1-2 times per week, providing roughly 1 inch of water each time. During the monsoon season, let the rainfall supplement your watering, but be sure to check the soil moisture levels regularly. In our extreme summer heat, you may need to water daily, especially if the plants are in full sun. Water at the base of the plants to avoid wetting the leaves, which can lead to fungal issues in our humid monsoon season.

Signs of underwatering include wilting leaves and slow growth. Overwatering can lead to yellowing leaves and root rot. A layer of mulch, such as straw or wood chips, can help retain soil moisture and regulate soil temperature, which is especially beneficial in our extreme climate.

You can expect your first harvest of mustard greens about 45 days after planting, so that lands in early April if you got an early start, and extends into late November with succession planting. Young leaves have a milder flavor, while larger leaves are spicier. Harvest before the plants start to flower, as bolting makes 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 production throughout the season. As the first frost approaches in mid- November, harvest any remaining leaves to enjoy before the cold weather sets in.

Mustard greens can encounter a few common problems in the Desert Southwest. Here’s how to handle them:

Flea Beetles

• What it looks like: Tiny round holes (shot-hole pattern) in leaves, especially on young seedlings. You might see small, dark beetles jumping when disturbed.
• What causes it: These small jumping beetles feed on the leaves. They're most damaging to small, young plants, and thrive in our warm, dry conditions.
• How to fix/prevent it: Use row covers to protect seedlings during their vulnerable stage. Delay planting until plants are larger and stronger. Kaolin clay coating can deter them. Neem oil spray can help. Interplant with basil or catnip. Healthy, vigorous plants often outgrow the damage.

Aphids

• What it looks like: Clusters of tiny soft-bodied insects (green, black, or white) on stems and leaf undersides. Sticky honeydew residue. Curled or distorted new growth.
• What causes it: These sap-sucking insects reproduce rapidly, especially in warm weather. Ant colonies may "farm" them for their honeydew.
• How to fix/prevent it: A strong water spray can knock them off. Encourage ladybugs and lacewings (natural predators). Insecticidal soap is effective for heavy infestations. Neem oil works systemically. Avoid excess nitrogen fertilizer, as it attracts them.

Cabbage Worms

• What it looks like: Smooth green caterpillars on brassica leaves. Irregular holes chewed in leaves. Dark green droppings. You might see white butterflies hovering around your plants.
• What causes it: These are the larvae of white cabbage butterflies. They 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 caterpillars when you see them. Interplant with aromatic herbs like thyme and sage. 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 rapidly.
• What causes it: Extended warm temperatures above the crop's comfort zone. Mustard greens 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. Mulch to keep the soil cool. Harvest before bolting progresses too far.

Desert Southwest Specific Challenges: The extreme heat and intense sun in our region can stress mustard greens, making them more susceptible to pests and bolting. Consistent watering is crucial, but be mindful of our monsoon season and adjust accordingly to avoid overwatering. Alkaline soil can also impact nutrient availability, so amend your soil with compost to improve its pH and fertility.

Good companions for mustard greens include onions and garlic, whose strong scents can deter pests. Beets are also beneficial, as they don't compete for the same nutrients in the soil. Dill attracts beneficial insects that prey on pests like aphids and cabbage worms. Lettuce can provide ground cover, helping to keep the soil cool and moist, which is especially important in our Desert Southwest heat.

Avoid planting mustard greens near strawberries or tomatoes. Strawberries can be susceptible to similar fungal diseases, and tomatoes can stunt the growth of mustard greens.