Mustard Greens in Zone 8A — Northern California

Mustard greens offer a zesty kick to your Northern California garden and kitchen. Their peppery flavor adds depth to salads, stir-fries, and braised dishes, and they thrive in our Mediterranean climate's mild winters and long growing season. You'll get a lot of satisfaction from growing your own, especially because they're so quick to mature.

Our dry summers and occasional water restrictions mean we need to be smart about watering, and the heat can sometimes cause bolting. But with a little planning and attention to timing within our 255-day growing season, you can enjoy a continuous harvest of mustard greens for much of the year.

Starting mustard greens indoors gives you a head start, but isn't always necessary in our mild climate. If you want to get a jump on the season, aim to sow seeds indoors from late January through mid February, about 3 weeks before you plan to transplant them outside.

Use seed trays or small pots filled with a good seed-starting mix. Keep the soil consistently moist by bottom watering – set the tray in a shallow dish of water and let the soil soak it up from the bottom. Provide warmth with a heat mat and plenty of light with grow lights. Given our early springs, this method can help you get your first harvest even sooner.

Transplant your mustard greens seedlings outdoors from late February through early April. Before transplanting, harden them off by gradually exposing them to outdoor conditions for about a week.

Choose a spot with full sun to partial shade. Space the plants 6-12 inches apart. Keep an eye on the weather forecast – a late frost can still happen at this time, so be prepared to cover your seedlings if necessary.

Direct sowing mustard greens is a simple and effective method, especially with our long growing season. You can direct sow from early February through late September, giving you multiple opportunities for successive plantings.

Prepare the soil by loosening it and adding compost or other organic matter. Sow seeds about ½ inch deep and 6-12 inches apart. Keep the soil consistently moist until the seedlings emerge. Direct sowing is a great option if you want a continuous supply of mustard greens without the hassle of transplanting.

Mustard greens need consistent moisture to thrive, but they don't like soggy soil. In our Northern California climate, this means paying close attention to your watering schedule, especially during our dry summers.

During the cooler spring and fall months, you'll likely only need to water once or twice a week, depending on rainfall. During the hotter summer months, increase watering to every other day or even daily, especially if they're in full sun. Stick your finger about 2 inches deep into the soil – if it feels dry, it's time to water. Aim for about 1 inch of water per week. Water at the base of the plants to avoid wetting the leaves, which can lead to fungal diseases in some microclimates.

Underwatering will cause the leaves to wilt and become more pungent (and encourages bolting). Overwatering can lead to root rot and yellowing leaves. A layer of mulch, like straw or wood chips, will help retain moisture in the soil and keep the roots cool during the summer heat.

You can expect your first harvest of mustard greens from late March through late November, about 45 days after planting. Harvest young leaves for a milder flavor, or wait for the leaves to mature for a spicier kick.

To harvest, simply snip off the outer leaves with scissors or a knife, leaving the inner leaves to continue growing. This will allow for continuous production throughout the season. As our first frost approaches around mid- November, harvest any remaining leaves to use in your favorite recipes or consider covering the plants to extend the harvest a bit longer.

Here are some common issues you might encounter while growing mustard greens in Northern California:

Flea Beetles

• What it looks like: Tiny round holes (shot-hole pattern) in leaves. You might see small dark beetles that jump when disturbed.
• What causes it: These small jumping beetles love to feed on the leaves of brassicas, especially young plants.
• How to fix/prevent it: Row covers are your best friend for protecting seedlings. You can also delay planting until your plants are larger and stronger. Kaolin clay can create a barrier, and neem oil spray can help control infestations. Companion planting with basil or catnip can also deter them.

Aphids

• What it looks like: Clusters of tiny soft-bodied insects (green, black, or white) on stems and leaf undersides. You'll also notice sticky honeydew residue and curled or distorted new growth.
• What causes it: These sap-sucking insects reproduce rapidly, especially in warm weather. Ants often "farm" them for their honeydew.
• How to fix/prevent it: A strong spray of water can knock them off. Encourage ladybugs and lacewings to visit your garden. Insecticidal soap is effective for heavy infestations, and neem oil works systemically. Avoid over-fertilizing with nitrogen, which attracts them.

Cabbage Worms

• What it looks like: Smooth green caterpillars munching on your brassica leaves. You'll see irregular holes and dark green droppings. Keep an eye out for white butterflies fluttering around.
• What causes it: These are the larvae of those 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 against cabbage worms. Floating row covers will prevent the butterflies from laying eggs. Handpick any caterpillars you find. Interplant with aromatic herbs like thyme or sage to deter them, and encourage parasitic wasps.

Bolting in Heat

• What it looks like: Your mustard greens will send up a flower stalk. The leaves become tough and bitter.
• What causes it: Mustard greens are a cool-season crop, and they bolt when temperatures rise. Days consistently above 80°F will trigger bolting.
• 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. Harvest promptly before bolting progresses too far.

Northern California Specific Challenges: Our moderate-to-hot summers and dry-summer rainfall patterns mean you need to be vigilant about watering to prevent bolting. Pay attention to microclimates in your yard, as some areas may be significantly hotter than others. Drought conditions and potential water restrictions may require you to prioritize watering your mustard greens, especially during the peak of summer.

Mustard greens benefit from companion planting. Onions and garlic are great companions because their strong scent deters pests. Beets help loosen the soil and provide nutrients. Dill attracts beneficial insects like ladybugs, which prey on aphids. Lettuce provides ground cover and helps retain moisture in the soil.

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