Mustard Greens in Zone 7A — Pacific Northwest

Mustard greens are a fantastic addition to any Pacific Northwest garden, offering a spicy kick to salads and stir-fries. They're incredibly versatile, thriving in our mild summers and cool nights, which actually enhances their flavor. Plus, the satisfaction of harvesting fresh greens from your garden, especially during our long, mild fall, is hard to beat.

While we enjoy a fairly long growing season of around 183 days here, our wet springs and relatively short bursts of true heat can present some challenges. Don't worry, though – with a little planning and attention to timing, you can easily grow a bountiful crop of mustard greens.

Starting mustard greens indoors is an option, but honestly, it's usually not necessary in our climate unless you're itching for a super early start. If you do want to get a jump on the season, start your seeds indoors from early to late March, about three weeks before you plan to transplant them outdoors.

Use seed trays with a good seed-starting mix, provide warmth (a heat mat helps), and ensure they get plenty of light – a grow light is best, especially with our overcast spring days. Remember to water from the bottom to encourage strong root growth and prevent damping off.

You can transplant your mustard greens seedlings outdoors from early April through mid May, once the soil has warmed up a bit. Before transplanting, harden them off by gradually exposing them to outdoor conditions for about a week. This prevents shock.

Space them 6-12 inches apart to allow for good air circulation and growth. Keep an eye on the weather forecast; a late frost can still happen, so be prepared to cover them if needed.

Direct sowing is the most common and often the easiest way to grow mustard greens here in the PNW. You can direct sow from late March through late August, giving you multiple opportunities for successive plantings.

Prepare your soil by loosening it and adding some compost. Mustard greens prefer soil temperatures around 60-70°F for optimal germination. Sow seeds 1/4 inch deep and space them 6-12 inches apart, or sow them closer and thin later.

Watering is crucial for mustard greens, especially during our dry summer months. While we don't get the scorching heat of other regions, consistent moisture is key to preventing bolting and keeping the leaves tender. Aim to keep the soil consistently moist, but not waterlogged.

During our wet springs, you might not need to water much at all – let the rain do the work! Once the dry summer months arrive, check the soil moisture regularly using the finger test: 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 in our sometimes humid conditions.

Signs of underwatering include wilting leaves and a generally stressed appearance. Overwatering, on the other hand, can lead to yellowing leaves and root rot. Mulching around your mustard greens with straw or wood chips helps retain moisture and regulate soil temperature, which is especially beneficial during our mild summers.

You can expect your first harvest of mustard greens from early May through late October, depending on when you planted. Mustard greens are ready to harvest about 45 days after planting.

Harvest young leaves for a milder flavor, or wait for the larger, more mature leaves for a spicier kick. Pick the leaves before the plant starts to flower, as bolting will make the leaves bitter. To harvest, simply snip off the outer leaves, leaving the inner ones to continue growing. This allows for continuous harvesting throughout the season.

As our first frost approaches around mid- October, you can extend your harvest by covering the plants with a frost blanket. This will protect them from the cold and allow you to enjoy fresh mustard greens for a bit longer.

Here are some common problems you might encounter with mustard greens in the Pacific Northwest:

Flea Beetles

• What it looks like: Tiny round holes (shot-hole pattern) in the leaves. You'll see small, dark beetles that jump when disturbed. The worst damage is usually on young seedlings.
• What causes it: These are small jumping beetles that feed on the leaves. They're most damaging to small, young plants and are very common in spring.
• How to fix/prevent it: Use row covers to protect seedlings during their vulnerable stage. You can also delay planting until the plants are larger and more resilient. Try coating the leaves with kaolin clay, or spray with neem oil. Interplanting with basil or catnip can also help deter them.

Aphids

• What it looks like: Clusters of tiny soft-bodied insects (green, black, or white) on stems and leaf undersides. You might also notice sticky honeydew residue and curled or distorted new growth.
• What causes it: These are sap-sucking insects that reproduce rapidly, especially in warm weather. Ant colonies may 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 can be used for heavy infestations, and neem oil works systemically. Avoid excess nitrogen fertilizer, as it attracts them.

Cabbage Worms

• What it looks like: Smooth green caterpillars on the leaves. You'll see irregular holes chewed in the leaves, and dark green droppings. White butterflies hovering around the plants are a sign they're laying eggs.
• What causes it: These are the larvae of white cabbage butterflies. There can be multiple generations per season if we get a warm summer.
• How to fix/prevent it: Bt spray is very effective. Floating row covers can prevent the butterflies from laying eggs. Handpick the caterpillars whenever you see them. Interplant with aromatic herbs like thyme or sage, and encourage parasitic wasps.

Bolting in Heat

• What it looks like: The plant sends up a flower stalk, and the leaves become tough and bitter. The harvest quality declines significantly.
• What causes it: This happens when temperatures rise for an extended period. Mustard greens are a cool-season crop and will bolt when days consistently exceed 80°F.
• How to fix/prevent it: Time your plantings for cool weather in spring and fall. Choose bolt-resistant varieties. Provide shade during warm spells, and mulch to keep the soil cool. Harvest the leaves before bolting progresses too far.

Pacific Northwest Specific Challenges: Our mild summers generally help prevent bolting, but unexpected heat waves can still trigger it, so be prepared to provide shade. The dry-summer climate means consistent watering is crucial to prevent stress. Late blight isn't a direct issue for mustard greens, but keeping good air circulation helps prevent other fungal diseases that can thrive in our often-damp springs. Slugs can also be a minor issue, especially with young plants, so use your preferred slug control methods.

Companion planting can be a great way to improve the health and yield of your mustard greens.

Good companions include onions and garlic, as their strong scent can help deter pests like aphids and flea beetles. Beets are also a good choice, as they don't compete for the same nutrients. Dill is another beneficial companion, attracting beneficial insects that prey on pests. Lettuce can provide ground cover, helping to retain moisture and suppress weeds.

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