Mustard Greens in Zone 8B — Northern California

Mustard greens thrive in our Northern California climate, offering a spicy kick to your salads and stir-fries. Their peppery flavor is especially welcome as we transition from the cool, wet months to our long, mild springs and manageable summers. Plus, they're incredibly versatile in the kitchen.

While we NorCal gardeners contend with drought and occasional heat waves, mustard greens are surprisingly resilient when planted at the right time. Our long growing season, which can stretch for 269 days, gives you plenty of opportunities to enjoy this leafy green.

Starting mustard greens indoors gives you a jumpstart, especially for an early spring harvest. Sow seeds indoors from mid January through early February, about three weeks before you plan to transplant. Use seed trays with a good seed-starting mix, keep them consistently moist with bottom watering, and provide warmth and light.

Starting indoors isn't always essential, since we have such a long growing season here in Zone 8B. However, it can be helpful if you want to get a head start or if you're dealing with a particularly wet early spring.

Transplant your mustard greens seedlings outdoors from mid February through late March, once they have a few true leaves. Before transplanting, harden them off by gradually exposing them to outdoor conditions for about a week. This helps them adjust to the NorCal weather and prevents transplant shock.

Space them 6-12 inches apart in well-drained soil. Keep an eye on the forecast – a late cold snap can happen in our region, so be prepared to cover them if necessary.

Direct sowing is a great option for mustard greens in our mild climate. Sow seeds directly into the garden from early February through late September. This gives you a long window for succession planting and continuous harvests.

Prepare the soil by loosening it and removing any rocks or debris. Sow seeds 1/4 inch deep and 6-12 inches apart. Keep the soil consistently moist until germination. Direct sowing is easy, but seedlings might be more vulnerable to pests than transplants.

Watering is key to happy mustard greens in our dry Northern California climate. While they aren't drought-tolerant, consistent moisture prevents bolting and keeps those leaves tender. During our dry summers, this means paying close attention.

Aim to keep the soil consistently moist, but not waterlogged. Stick your finger about 2 inches deep into the soil – if it feels dry, it's time to water. During the hotter months, your mustard greens may need about 1-2 inches of water per week, especially if you're growing in full sun.

Water at the base of the plants to avoid wetting the leaves, which can encourage fungal diseases in our sometimes humid microclimates. Overwatering can lead to yellowing leaves, while underwatering causes the leaves to become tough and spicy, and may trigger premature bolting. A layer of mulch, like straw or wood chips, helps retain moisture and regulate soil temperature.

You can expect your first harvest of mustard greens around mid March through early December, about 45 days after planting. The timing will depend on when you sowed your seeds. Young leaves have a milder flavor, while larger leaves pack more of a peppery punch.

Harvest by snipping off the outer leaves, leaving the inner leaves to continue growing. This cut-and-come-again method encourages continuous production throughout the season. Be sure to harvest before the plants start to flower, as bolting makes the leaves bitter.

As our first frost approaches in late November, harvest any remaining leaves. You can also cover the plants with a frost blanket to extend the harvest a bit longer.

Here are some common problems you might encounter with mustard greens in Northern California:

Flea Beetles

• What it looks like: Tiny round holes in the leaves, creating a "shot-hole" pattern. You might see small, dark beetles jumping when disturbed.
• What causes it: These small beetles feed on the leaves, especially of young plants. They're more prevalent during dry spells.
• How to fix/prevent it: Use row covers to protect seedlings. Delay planting until plants are larger and more resilient. You can also try spraying with kaolin clay or neem oil.

Aphids

• What it looks like: Clusters of tiny green, black, or white insects on stems and leaf undersides. Sticky honeydew residue and curled or distorted new growth.
• What causes it: Aphids are sap-sucking insects that thrive in warm weather. Ants often protect them in exchange for honeydew.
• How to fix/prevent it: A strong spray of water can knock them off. Encourage beneficial insects like ladybugs. Insecticidal soap works well for heavy infestations.

Cabbage Worms

• What it looks like: Smooth green caterpillars chewing irregular holes in the leaves. Dark green droppings are often present. You might see white cabbage butterflies fluttering around.
• What causes it: These are the larvae of cabbage butterflies. They can have multiple generations in our long growing season.
• How to fix/prevent it: Bt spray is very effective. Use floating row covers to prevent butterflies from laying eggs. Handpick the caterpillars when you see them.

Bolting in Heat

• What it looks like: The plant sends up a flower stalk, and the leaves become tough and bitter.
• What causes it: Mustard greens are a cool-season crop, and they bolt (go to seed) when temperatures consistently rise above their comfort zone.
• How to fix/prevent it: Time your plantings for cooler weather in spring and fall. Choose bolt-resistant varieties. Provide shade during warm spells and use mulch to keep the soil cool.

Northern California Specific Challenges: Our moderate-to-hot summers and dry conditions can stress mustard greens, making them more susceptible to pests and bolting. Consistent watering and strategic planting times are crucial for success.

Companion planting can really boost your mustard greens in Northern California. Onions and garlic are great companions because their strong scent deters pests like aphids and cabbage worms. Beets are also beneficial, as they don't compete for the same nutrients and can help loosen the soil. Dill attracts beneficial insects like ladybugs, which prey on aphids. Lettuce provides ground cover, helping to retain moisture in our dry climate.

Avoid planting mustard greens near strawberries or tomatoes. Strawberries are susceptible to similar fungal diseases, which can spread to your mustard greens. Tomatoes can stunt the growth of mustard greens, and vice versa.