Mustard Greens in Zone 7B — Pacific Northwest

Mustard greens are a fantastic addition to any Pacific Northwest garden. Their peppery bite adds zing to salads and stir-fries, and they're surprisingly easy to grow in our mild summers and cool nights. Plus, the satisfaction of harvesting fresh greens from your own backyard, even as the weather cools down, is hard to beat.

Even with our relatively long, 193-day growing season, we face challenges like cool spring soil and the occasional heat spike. But with a little planning and attention to timing, you can enjoy a bountiful harvest of mustard greens from spring well into fall.

Starting mustard greens indoors isn't strictly necessary in our climate, but it can give you a head start, especially if you're eager for an early spring harvest. If you choose to go this route, sow seeds indoors from early to late March, about three weeks before you plan to transplant them.

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. Provide warmth and plenty of light, either from a sunny windowsill or a grow light. Since spring can be slow to warm up, this gives your seedlings a jumpstart.

Once the weather begins to settle in early April through mid May, and your mustard greens seedlings have a few true leaves, it's time to transplant them outdoors. Before planting, harden them off by gradually exposing them to outdoor conditions for about a week.

Choose a spot with full sun to partial shade, and space the plants 6-12 inches apart. Be mindful of late spring showers and overcast spring days that can keep the soil cool, potentially slowing down growth.

Direct sowing is a simple and effective way to grow mustard greens in the Pacific Northwest. Sow seeds from mid March through late August for a continuous harvest.

Prepare the soil by loosening it and removing any rocks or debris. Sow seeds about ½ inch deep and 6-12 inches apart. Keep the soil consistently moist until the seedlings emerge. Direct sowing works particularly well for late summer/early fall crops, as the soil is warmer and the risk of bolting is lower.

Mustard greens need consistent moisture to thrive, but overwatering can be just as detrimental as underwatering, especially in our climate. Aim to keep the soil consistently moist, but not soggy.

During our wet springs, you may not need to water at all, relying on rainfall to do the job. But as the dry summer months approach, check the soil moisture regularly. Stick your finger about 2 inches deep into the soil – if it feels dry, it's time to water.

Generally, mustard greens need about 1 inch of water per week, either from rainfall or irrigation. Water at the base of the plants to avoid wetting the foliage, which can increase the risk of fungal diseases, although our dry summer humidity makes this less of a concern.

Signs of underwatering include wilting leaves and a bitter taste. Overwatering can lead to yellowing leaves and root rot. A layer of mulch, such as straw or wood chips, can help retain moisture and regulate soil temperature during our mild summer heat.

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

Larger leaves will be spicier and can become tough, especially if the plant is starting to bolt. To harvest, simply snip off the outer leaves with scissors or a knife, leaving the inner leaves to continue growing. This allows for continuous harvesting throughout the season.

As the first frost approaches in late October, harvest any remaining leaves, even if they're small. You can also try covering the plants with a frost blanket to extend the harvest a bit longer, taking advantage of our long, mild fall.

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

Flea Beetles

• What it looks like: Tiny round holes (shot-hole pattern) in leaves, especially on young seedlings. Small, dark beetles jump when disturbed.
• What causes it: Small jumping beetles that feed on leaves. Most damaging to small, young plants. They seem to thrive in the cool spring soil.
• How to fix/prevent it: Use row covers to protect seedlings. Delay planting until plants are larger. Try kaolin clay or neem oil spray. Interplant with basil or catnip. Healthy plants often outgrow the damage.

Aphids

• What it looks like: Clusters of tiny soft-bodied insects (green, black, or white) on stems and leaf undersides. Sticky honeydew residue. Curled or distorted new growth.
• What causes it: Rapid-reproducing sap-sucking insects. Populations can explode, even in our mild summers.
• How to fix/prevent it: Strong water spray knocks them off. Encourage ladybugs and lacewings. Insecticidal soap for heavy infestations. Neem oil works systemically. Avoid excess nitrogen fertilizer.

Cabbage Worms

• What it looks like: Smooth green caterpillars on brassica leaves. Irregular holes chewed in leaves. Dark green droppings. White butterflies hovering around plants.
• What causes it: Larvae of white cabbage butterflies.
• How to fix/prevent it: Bt spray is very effective. Floating row covers prevent egg laying. Handpick caterpillars. Interplant with aromatic herbs like thyme or sage.

Bolting in Heat

• What it looks like: The plant sends up a flower stalk. Leaves become tough and bitter.
• What causes it: Extended warm temperatures. Mustard greens bolt when days consistently exceed 80°F, which can happen during our mild summers.
• How to fix/prevent it: Time plantings for cool weather (spring/fall). Choose bolt-resistant varieties. Provide shade during warm spells. Mulch to keep soil cool. Harvest before bolting progresses.

Pacific Northwest Specific Challenges: Late blight isn't a major concern for mustard greens themselves, but it's always lurking in our region. Cool spring soil can slow growth, making seedlings more vulnerable to pests. While we don't often get sustained periods above 90°F, even a few days of warmer weather can trigger bolting, so be vigilant and provide shade if needed. Slugs can also be an issue, especially in damp areas, so use appropriate control measures.

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

Avoid planting mustard greens near strawberries or tomatoes. Strawberries are susceptible to similar fungal diseases, increasing the risk of problems. Tomatoes can stunt the growth of mustard greens, as they compete for the same resources.