Mustard Greens in Zone 10B — Southern California

Mustard greens bring a peppery zing to your salads and stir-fries, and they're incredibly easy to grow in our Southern California climate. Their fast growth and tolerance for our mild winters make them a rewarding addition to your year-round harvest. Plus, they're packed with nutrients, offering a healthy boost to your meals.

Sure, we have our challenges here in SoCal, from occasional drought to summer heat inland. But with careful timing and water-wise practices, you can enjoy a bountiful crop of mustard greens. Our long 355-day growing season gives you plenty of opportunities to plant and harvest.

Starting mustard greens indoors isn't always necessary here in Southern California, given our mild climate. However, it can give you a head start, especially if you're aiming for a very early harvest. If you want to start indoors, aim for late November through mid December, about three weeks before you plan to transplant.

Use seed trays or small pots filled with a good seed-starting mix. Keep them warm and provide plenty of light, either from a sunny window or a grow light. Bottom watering helps prevent damping off; set the tray in a shallow dish of water and let the soil absorb it from below. Since our spring character is very-early, this head start can get you harvesting sooner.

Transplant your mustard green seedlings outdoors from late December through early February. This timing lets them establish before any intense summer heat inland. Before transplanting, harden them off by gradually exposing them to outdoor conditions for about a week.

Space the seedlings 6-12 inches apart in well-drained soil. Be mindful of potential cool, wet weather during this period; protect young transplants from excessive rain or unexpected cold snaps. A little protection can go a long way.

Direct sowing mustard greens is a straightforward option here in Southern California, and often the most convenient. You can sow seeds directly into the garden from mid December through early November, taking advantage of our long growing season. Keep in mind that summer heat inland can affect germination rates, so providing some afternoon shade during the hottest months can be helpful.

Prepare the soil by loosening it and adding compost. Sow seeds about ¼ inch deep and keep the soil consistently moist. Thin seedlings to 6-12 inches apart once they emerge. Direct sowing is simple but remember to monitor for pests like flea beetles, especially when plants are young.

Consistent moisture is key for happy mustard greens here in Southern California. While not drought-tolerant, smart watering practices will keep them thriving. Aim to keep the soil consistently moist, especially during our drier periods.

During the cooler months, when we get the bulk of our 10-20 inches of rainfall, you might only need to supplement with watering once or twice a week. As temperatures rise in the spring and summer, increase watering to 2-3 times per week, possibly more during Santa Ana wind events. Stick your finger about 2 inches deep into the soil; if it feels dry, it's time to water. Generally, aim for about 1 inch of water per week, adjusting based on rainfall and temperature.

Water at the base of the plants to avoid wetting the leaves, which can encourage fungal diseases, even with our low-to-moderate humidity. Signs of underwatering include wilting leaves and a bitter taste, while overwatering can lead to yellowing leaves and root rot. Applying a layer of mulch, like straw or wood chips, helps retain soil moisture and regulate temperature, a crucial step during our summer heat inland.

In Southern California, you can expect your first harvest of mustard greens about 45 days after planting, typically from late to early January, depending on when you sowed. Harvest young leaves when they are about 4-6 inches long for a milder flavor; larger leaves will have a spicier kick. Pick leaves before the plant starts to flower, as bolting makes the leaves bitter.

To harvest, simply snip off the outer leaves, leaving the inner ones to continue growing. This cut-and-come-again method encourages continuous production throughout the season. Even as we approach our typical first frost in late December, you can often extend the harvest by covering plants during any unexpected cold snaps.

Mustard greens, like any crop, can face challenges in Southern California gardens. Keep an eye out for these common problems:

Flea Beetles

• What it looks like: Tiny round holes (shot-hole pattern) in leaves. You'll see small dark beetles that jump when disturbed. The worst damage happens to young seedlings.
• What causes it: These small jumping beetles feed on leaves of brassicas. They're 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. Coat leaves with kaolin clay. Spray with neem oil. 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. You might notice sticky honeydew residue and curled or distorted new growth.
• What causes it: These sap-sucking insects reproduce rapidly. Populations explode in warm weather. Ant colonies may farm them for honeydew.
• How to fix/prevent it: A strong water spray knocks them off. Encourage ladybugs and lacewings (natural predators). Use insecticidal soap for heavy infestations. Neem oil works systemically. Avoid excess nitrogen fertilizer, which 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 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 prevent egg laying. Handpick caterpillars when you see them. Interplant with aromatic herbs like thyme or sage. Encourage parasitic wasps.

Bolting in Heat

• What it looks like: The cool-season crop sends up a flower stalk when temperatures rise. Leaves become tough and bitter, and harvest quality declines.
• What causes it: Extended warm temperatures above the crop's comfort zone cause bolting. Brassicas bolt when days consistently exceed 80°F.
• How to fix/prevent it: Time plantings for cool weather (spring/fall). Choose bolt-resistant varieties. Provide shade during warm spells. Mulch to keep the soil cool. Harvest before bolting progresses.

Southern California Specific Challenges: Our hot heat inland can stress mustard greens, making them more susceptible to bolting and pests. The low-to-moderate humidity can help reduce fungal diseases, but also means you need to be vigilant about watering. Winter-wet rainfall can sometimes lead to waterlogged soil, so ensure good drainage.

Companion planting can give your mustard greens a boost in Southern California. Plant onions and garlic nearby to deter pests like aphids and cabbage worms with their strong scent. Beets are also good companions, as they don't compete for the same nutrients and can help improve soil structure.

Dill attracts beneficial insects like ladybugs and lacewings, which prey on aphids and other pests. Lettuce provides ground cover, helping to keep the soil cool and moist, which is especially important during warmer months. Avoid planting strawberries or tomatoes near mustard greens, as they can attract similar pests and diseases, increasing the risk of problems in your garden.