Mustard Greens in Zone 8B — Pacific Northwest

Mustard greens pack a peppery punch that brightens up any dish, and they're surprisingly easy to grow here in the Pacific Northwest. Our cool nights actually enhance their flavor, giving them a depth you won't find just anywhere. Plus, a steady supply of fresh greens straight from your garden is incredibly rewarding.

Sure, we have our quirks – like cool soil in the spring and the occasional slug – but mustard greens are adaptable and fast-growing. With a 210-day growing season, you've got plenty of time to get several harvests. Timing is key to avoiding bolting in the summer heat.

Starting mustard greens indoors isn't essential, but it can give you a head start, especially with our sometimes-slow springs. If you want to get a jump on the season, sow seeds indoors from late February through mid March, about three weeks before you plan to transplant.

Use seed trays with a good seed-starting mix, and keep them warm – a heat mat can help. Make sure they get plenty of light, either from a grow light or a very sunny windowsill. Bottom watering helps prevent damping off; just set the tray in a shallow dish of water and let the soil soak it up.

Transplant your mustard greens seedlings outdoors from late March through early May, once the soil has warmed up a bit. Before you plant them out, harden them off for about a week by gradually exposing them to outdoor conditions.

Start with an hour or two of shade, and slowly increase the time and sun exposure each day. Space them 6-12 inches apart, depending on the variety and how large you want them to grow. Keep an eye on the forecast – a late frost can still happen, so be prepared to cover them if needed.

Direct sowing mustard greens is a great option here in the PNW, and it's my preferred method. You can sow seeds directly into the garden from early March through early September for a continuous harvest.

Prepare the soil by loosening it and adding some compost. Mustard greens prefer soil temperatures around 60-70°F for optimal germination. Sow seeds about ½ inch deep and space them 6-12 inches apart. Thin seedlings as they grow to give them enough room. Direct sowing works well if you succession plant every few weeks.

Mustard greens need consistent moisture, especially during our dry summer months. While our summers are mild, they're still dry, and drought stress can make the leaves tougher and spicier.

During the wet springs, you might not need to water much at all, but once the dry season hits, check the soil regularly. Stick your finger about two inches deep – if it feels dry, it's time to water. Aim for about an 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.

Wilting leaves are a sign of underwatering, while yellowing leaves can indicate overwatering. A layer of mulch, like straw or wood chips, will help retain moisture and keep the soil cool.

You can expect your first harvest of mustard greens about 45 days after planting, which means you can start enjoying them as early as late April if you started early or direct sowed in March. Continue harvesting through early November.

Harvest young leaves for a milder flavor; larger leaves will be spicier. Pick the outer leaves as needed, leaving the inner ones to continue growing for a continuous harvest. Harvest before the plants start to flower (bolt), as the leaves will become bitter.

As the first frost approaches in early November, harvest any remaining leaves to enjoy before the cold damages them. You can also cover the plants with a frost blanket to extend the harvest a bit longer.

Mustard greens are relatively easy to grow, but here are a few common problems you might encounter in the Pacific Northwest:

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: Small jumping beetles that feed on the leaves. They thrive in dry conditions and are most damaging to small, young plants.
• How to fix/prevent it: Use row covers to protect seedlings. You can also delay planting until the plants are larger and more resilient. Kaolin clay coating deters them. Neem oil spray can help, and interplanting with basil or catnip may repel them.

Aphids

• What it looks like: Clusters of tiny, soft-bodied insects (green, black, or white) on stems and leaf undersides. Sticky honeydew residue and curled or distorted new growth.
• What causes it: Rapid-reproducing sap-sucking insects. They love our mild summers.
• How to fix/prevent it: A strong spray of water can knock them off. Encourage ladybugs and lacewings, which are natural predators. Insecticidal soap works well, and neem oil can be effective. Avoid over-fertilizing with nitrogen, which attracts them.

Cabbage Worms

• What it looks like: Smooth green caterpillars on the leaves, irregular holes chewed in the leaves, dark green droppings, and white butterflies hovering around the plants.
• What causes it: Larvae of white cabbage butterflies.
• How to fix/prevent it: Bt spray is very effective. Floating row covers prevent the butterflies from laying eggs. Handpick caterpillars when you see them. Interplant with aromatic herbs like thyme or sage to deter the butterflies.

Bolting in Heat

• What it looks like: The plant sends up a flower stalk, and the leaves become tough and bitter.
• What causes it: Extended warm temperatures. Mustard greens are a cool-season crop, and they bolt when the 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 before bolting progresses too far.

Pacific Northwest Specific Challenges: While late blight isn't a direct threat to mustard greens, the conditions that favor it (wet springs) can also create problems for other crops in your garden. Cool soil in the spring can slow down germination, so be patient or start indoors. While our summers are mild, the dry-summer humidity and rainfall patterns mean you need to be vigilant about watering to prevent bolting and ensure a good harvest. Also, slugs love mustard greens, so put out your preferred slug control method (beer traps, copper tape, etc.).

Mustard greens benefit from companion planting. Onions and garlic help deter pests like aphids and flea beetles with their strong scent. Beets are good companions because they don't compete for the same nutrients, and their presence can improve the soil structure. Dill attracts beneficial insects like ladybugs, which prey on aphids. Lettuce provides ground cover, helping to keep the soil cool and moist.

Avoid planting mustard greens near strawberries or tomatoes. Strawberries are susceptible to similar fungal diseases, and tomatoes can attract pests that also bother mustard greens.