Mustard Greens in Zone 9A — Northern California

Mustard greens bring a delightful peppery bite to your Northern California garden, perfect for adding zest to salads or a kick to stir-fries. Their quick growth and tolerance of our mild winters mean you can enjoy fresh greens almost year-round. Imagine harvesting vibrant leaves even as the morning fog rolls in!

Our region presents some gardening challenges, like periodic drought and the occasional heat spike. But with careful timing and water-wise gardening practices, mustard greens thrive here. With our long 288-day growing season, you'll have plenty of opportunities to sow and harvest.

Starting mustard greens indoors in Northern California is an option, especially if you want a head start on the season or are dealing with intense pest pressure early on. Sow seeds indoors from early to late January, about three weeks before you plan to transplant. Use seed trays filled with a good seed-starting mix, and keep them in a warm spot with plenty of light – a south-facing window or under grow lights works well.

Water gently from the bottom to avoid damping off. Since our spring comes early, indoor starting isn’t always necessary, but it can give you a jump on the season, especially in cooler microclimates.

Transplant your mustard greens seedlings outdoors from early February through mid 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 sun and wind.

Space plants 6-12 inches apart in well-drained soil. Keep an eye out for late frosts – our weather can be unpredictable, even in early spring. Row covers provide extra protection if needed.

Direct sowing mustard greens is a breeze in our Northern California climate, and often the easiest method! Sow seeds directly into the garden from late January through early October for a continuous harvest. Prepare the soil by loosening it and adding compost.

Plant seeds about ½ inch deep and space them 6-12 inches apart. Keep the soil consistently moist until germination. Direct sowing is great because it avoids transplant shock, but seedlings can be more vulnerable to pests.

Watering is crucial for mustard greens in our dry Northern California climate, especially during the summer months. While they're not drought-tolerant, consistent moisture keeps them happy and prevents bolting. Aim to keep the soil consistently moist, but not soggy.

During the cooler months (late fall through early spring), you might only need to water once or twice a week, depending on rainfall. In the hotter, drier summer, increase watering to every other day, or even daily during heat waves. Stick your finger about two inches deep into the soil – if it feels dry, it's time to water. Aim for about 1 inch of water per week, adjusting based on rainfall. Water at the base of the plants to avoid wetting the leaves, which can encourage fungal diseases in our humid microclimates.

Signs of underwatering include wilting leaves and slow growth. Overwatering can lead to yellowing leaves and root rot. A layer of mulch, like straw or wood chips, helps retain moisture and regulate soil temperature, which is especially important during our dry summers.

You can expect your first harvest of mustard greens from early March through mid December, about 45 days after planting. Harvest young leaves when they're about 4-6 inches long for a milder flavor. Larger, more mature leaves will have a spicier kick. Always harvest before the plant starts to flower (bolt), as the leaves will become bitter.

To harvest, simply snip off the outer leaves with scissors or a knife, leaving the inner leaves to continue growing. This cut-and-come-again method allows for continuous production throughout the season. As our first frost approaches in early December, you can extend your harvest by covering the plants with a frost blanket.

Mustard greens can face a few common problems in Northern California gardens:

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: Row covers are your best friend for protecting seedlings. Delay planting until plants are larger and more resilient. A coating of kaolin clay can also deter them. Neem oil spray can help control infestations. Interplanting with basil or catnip may also help.

Aphids

• What it looks like: Clusters of tiny soft-bodied insects (green, black, or white) on stems and leaf undersides. You might also notice a sticky honeydew residue or curled, distorted new growth.
• What causes it: These sap-sucking insects reproduce rapidly, especially in warm weather. Ant colonies sometimes "farm" them for their honeydew.
• How to fix/prevent it: A strong spray of water can knock them off. Encourage ladybugs and lacewings, which are natural predators. Insecticidal soap is effective for heavy infestations. Neem oil also works well. Avoid over-fertilizing with nitrogen, as it attracts aphids.

Cabbage Worms

• What it looks like: Smooth green caterpillars munching on brassica leaves, leaving irregular holes. You might also see dark green droppings or white butterflies fluttering around your plants.
• What causes it: These are the larvae of white cabbage butterflies. They can have multiple generations per season in our mild climate.
• How to fix/prevent it: Bt spray (Bacillus thuringiensis) is very effective. Floating row covers will prevent butterflies from laying eggs. Handpicking caterpillars is also an option. Interplant with aromatic herbs like thyme or 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.
• What causes it: Mustard greens are a cool-season crop, and they bolt (go to seed) when temperatures rise. Extended warm temperatures above 80°F can 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 with shade cloth. Mulch to keep the soil cool. Harvest leaves frequently to delay bolting.

Northern California Specific Challenges: Our moderate-to-hot summers and periodic droughts mean you need to be vigilant about watering and providing shade during the hottest part of the day. Keep a close eye on your plants and adjust your care as needed.

Mustard greens love growing alongside onions and garlic, as their strong scent can deter pests. Beets are also excellent companions, as they don't compete for the same nutrients and can help loosen the soil. Dill attracts beneficial insects that prey on aphids and other pests. Lettuce provides ground cover, helping to keep the soil cool and moist.

Avoid planting mustard greens near strawberries or tomatoes. Strawberries are susceptible to some of the same pests as mustard greens, and tomatoes can stunt the growth of mustard greens. By choosing the right companions, you can create a thriving and productive garden in Northern California.