Mustard Greens in Zone 6B — Pacific Northwest

Mustard greens bring a peppery zing to your plate, thriving in our mild summers and cool nights. Their quick growth makes them incredibly rewarding, offering fresh greens from your garden even with our shorter growing season. Plus, the slightly spicy flavor is enhanced by our cool nights!

While we may not have the scorching heat some regions face, our cool soil in spring and the risk of late blight can be hurdles. Don't worry, though! With a bit of planning and attention to timing within our 162-day growing season, you can easily enjoy a bountiful harvest of mustard greens.

Starting mustard greens indoors isn't essential here in the PNW, but it can give you a head start, especially if we have a particularly overcast spring. If you want to get a jump on the season, sow seeds indoors mid-March through early April, about 3 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 sunny windowsill or under grow lights works well. Remember to water from the bottom to encourage strong root growth and prevent damping off, a common issue with our wet springs.

Transplant your mustard green seedlings outdoors from mid-April through late 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 helps them adjust to the cooler temperatures and stronger sunlight.

When transplanting, space the seedlings 6-12 inches apart. Keep an eye on the forecast – a late cold snap can stress young plants, so be ready to cover them if needed.

Direct sowing is an easy and effective way to grow mustard greens here. Sow seeds directly into the garden from early April through mid-August. This gives you a long window for successive plantings and a continuous harvest.

Prepare the soil by loosening it and adding some compost. Mustard greens prefer well-drained soil. Sow seeds about ½ inch deep and space them 6-12 inches apart. Keep the soil consistently moist until the seedlings emerge.

Our mild summers and dry-summer humidity mean you'll need to pay attention to watering, even though it's not as intense as in hotter climates. Aim to keep the soil consistently moist, but not waterlogged. A good rule of thumb is to water deeply once or twice a week, providing about 1 inch of water each time, especially during the drier summer months.

Use the "finger test" to check soil moisture – stick your finger about 2 inches into the soil. If it feels dry, it's time to water. Water at the base of the plants rather than overhead to minimize fungal diseases, which can be a concern with our wet springs.

Underwatering will cause the leaves to become tough and spicy, and can trigger bolting. Overwatering, on the other hand, can lead to root rot. A layer of mulch, like straw or shredded leaves, can help retain soil moisture and suppress weeds – a big help during our drier summer months.

You can expect your first harvest of mustard greens from mid-May through mid-October, about 45 days after planting. The best time to harvest is when the leaves are young and tender, usually around 4-6 inches long. These smaller leaves will have a milder flavor.

Larger, more mature leaves will be spicier, but still perfectly edible. Avoid harvesting once the plant starts to flower, 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 encourages continuous production throughout the season.

As our first frost approaches in early October, harvest any remaining leaves. Mustard greens can tolerate a light frost, but prolonged cold will damage them.

Here are some common problems you might encounter growing mustard greens in the PNW:

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 feed on the leaves. They're most damaging to small, young plants.
• How to fix/prevent it: Row covers are your best friend for protecting seedlings. Delay planting until plants are larger and more resilient. Kaolin clay can create a protective barrier. Neem oil can also help. Interplanting with basil or catnip can deter them.

Aphids

• What it looks like: Clusters of tiny green, black, or white insects on stems and leaf undersides. You might also see sticky honeydew residue and curled or distorted new growth.
• What causes it: These sap-sucking insects reproduce rapidly, especially when it warms up.
• How to fix/prevent it: A strong spray of water can knock them off. Encourage natural predators like ladybugs and lacewings. Insecticidal soap works well for heavy infestations. Avoid over-fertilizing with nitrogen, as it attracts aphids.

Cabbage Worms

• What it looks like: Smooth green caterpillars chewing irregular holes in leaves, leaving behind dark green droppings. You might also see white cabbage butterflies fluttering around.
• What causes it: These are the larvae of those white cabbage butterflies.
• How to fix/prevent it: Bt spray is very effective. Floating row covers will prevent the butterflies from laying eggs on your plants. Handpick the caterpillars whenever 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: Mustard greens are cool-season crops and bolt when temperatures consistently exceed 80°F.
• 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 before bolting progresses too far.

Pacific Northwest Specific Challenges: Our mild heat generally isn't a huge issue for bolting, but prolonged warm spells can still trigger it. Our dry-summer humidity helps reduce fungal diseases, but keep an eye out for aphids, which thrive in these conditions. Slugs can also be a problem, especially with young seedlings, so use your preferred slug control methods.

Mustard greens benefit from companion planting. Onions and garlic are great companions because their strong scent deters pests like aphids and flea beetles. Beets are also good companions, as they don't compete for the same nutrients and can even improve soil health. Dill attracts beneficial insects that prey on pests. Lettuce provides ground cover, helping to retain moisture and suppress weeds.

Avoid planting mustard greens near strawberries or tomatoes. Strawberries are susceptible to verticillium wilt, which can also affect mustard greens. Tomatoes can attract pests like aphids that may also target your mustard greens.