Mustard Greens in Zone 9B — Southern California

Mustard greens bring a zesty, peppery bite to your kitchen, and they're incredibly versatile. Here in Southern California, with our long growing season, you can enjoy a year-round harvest of these nutritious greens in salads, stir-fries, or even lightly sauteed. Plus, they thrive in our mild winters.

While we do face challenges like drought and the occasional heat wave, the timing for growing mustard greens makes it perfectly manageable. Our 334-day growing season means you can easily work around the extremes and still get a great crop.

Starting mustard greens indoors in Southern California is possible, but honestly, direct sowing is usually the way to go. However, if you want a jump start, especially for an early spring harvest, it's an option.

Start your seeds indoors from mid December through early January, about three weeks before you plan to transplant. Use seed trays with a good seed-starting mix, keep them warm (a heat mat helps), and provide plenty of light with a grow light. Bottom watering is key to prevent damping off. Given our very-early spring character, this can give you a head start.

Transplant your mustard greens seedlings outdoors from mid January through late February. Before you do, harden them off by gradually exposing them to outdoor conditions for about a week. This prevents shock.

Space the seedlings 6-12 inches apart. Keep an eye on the weather forecast – a late cold snap can happen, even here in SoCal. If frost is predicted, cover your seedlings with frost cloth.

Direct sowing mustard greens is easy and works well in Southern California. You can direct sow from late December through late October, giving you nearly year-round planting opportunities.

Prepare your soil by loosening it and mixing in some compost or aged manure. Soil temperatures should be at least 45°F for good germination. Sow seeds about 1/4 inch deep and space them 6-12 inches apart, or sow closer and thin later. This is a good option for succession planting to ensure a continuous harvest.

Mustard greens need consistent moisture to thrive, but overwatering can be just as bad as underwatering, especially with our occasional winter rains. Aim to keep the soil evenly moist, but not soggy.

During the cooler months (late fall through early spring), when we get most of our rainfall, you might only need to supplement with watering once a week or less, depending on the weather. In the hotter, drier months (late spring through early fall), you'll likely need to water every other day, or even daily during heat waves, especially if you're inland and dealing with the summer heat. 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, either from rainfall or irrigation. Water at the base of the plants to avoid wetting the leaves, which can encourage fungal diseases, especially with our low-to-moderate humidity. Wilting leaves are a sign of underwatering, while yellowing leaves can indicate overwatering. A layer of mulch, like straw or wood chips, helps retain moisture and keep the soil cool, which is particularly helpful during those hot inland summers.

You can expect your first harvest of mustard greens from mid February through early January, about 45 days after planting. The best time to harvest is when the leaves are young and tender.

Look for leaves that are about 4-6 inches long. Smaller leaves will have a milder flavor, while larger leaves tend to be spicier. To harvest, simply snip off the outer leaves with scissors or a knife, leaving the inner leaves to continue growing. This encourages continuous production.

As late December approaches and the possibility of our first frost looms, harvest any remaining mature leaves. While mustard greens are semi-hardy, a hard frost can damage them. You can also cover the plants with frost cloth to extend the harvest a bit longer.

Here are some common problems you might encounter growing mustard greens in Southern California:

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 love to feed on brassicas. They're most damaging to small, young plants, especially during dry spells.
• How to fix/prevent it: Use row covers to protect seedlings. Delay planting until plants are larger. Kaolin clay coating can deter them. Neem oil spray works too. Interplant with basil or catnip. Healthy, vigorous plants tend to 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 might farm them for honeydew.
• How to fix/prevent it: A strong water spray knocks 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 those white cabbage butterflies. They can 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 and sage. Encourage parasitic wasps.

Bolting in Heat

• What it looks like: The plant sends up a flower stalk. The leaves become tough and bitter.
• What causes it: Mustard greens are a cool-season crop and will bolt when temperatures rise consistently above their comfort zone. This is especially a concern during our summer heat inland.
• How to fix/prevent it: Time your plantings for cooler weather in 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.

Southern California Specific Challenges: Our hot, dry summers and occasional Santa Ana winds can stress mustard greens, making them more susceptible to pests and bolting. Consistent watering is crucial, and providing some afternoon shade during the hottest months can help. Also, be aware of fire season and take precautions to protect your garden from ash and potential fire hazards.

Mustard greens play well with some neighbors in the garden. Onions and garlic are great companions because their strong scent can deter pests like aphids and cabbage moths. Beets also make good companions, as they don't compete for the same nutrients and can help loosen the soil. Dill attracts beneficial insects that prey on pests, and lettuce provides ground cover to help retain moisture.

Avoid planting mustard greens near strawberries or tomatoes. Strawberries are susceptible to some of the same pests as mustard greens, potentially increasing pest pressure. Tomatoes can stunt the growth of mustard greens, possibly due to allelopathic chemicals they release into the soil.