Mustard Greens in Zone 8A — Pacific Northwest

Mustard greens are a fantastic addition to your Pacific Northwest garden. Their peppery bite adds zing to salads, stir-fries, and soups, and they thrive in our mild summers and cool nights. Plus, the satisfaction of harvesting fresh greens nearly year-round in our temperate climate is hard to beat.

While our wet springs and the risk of late blight can present challenges, careful timing and a few simple strategies will have you enjoying abundant harvests of mustard greens. Our 203-day growing season gives you plenty of opportunity to get it right.

Starting mustard greens indoors in late February through mid March can give you a jump start on the season, especially if you're eager for an early harvest. This is about 3 weeks before you intend to transplant them. Use seed trays or small pots filled with seed-starting mix, and keep them in a warm location with plenty of light – a sunny windowsill or under grow lights will work.

Bottom watering is a good trick; set the tray in a shallow dish of water and let the soil soak it up from the bottom. Remember, our springs here in the PNW can be slow to warm up, so starting indoors gives your mustard greens a head start before the cool soil sets in.

Transplant your mustard greens outdoors in late March through early May once they have a few true leaves and the weather has settled 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.

Space them 6-12 inches apart in well-drained soil. Keep an eye on the weather forecast; a late frost can still happen, so be prepared to cover them if necessary.

Direct sowing mustard greens is an easy and reliable method, especially for succession planting throughout the growing season. Sow seeds mid March through early September, directly into well-prepared soil. Mustard greens prefer soil temperatures between 45°F and 85°F for optimal germination.

Space seeds 6-12 inches apart, and thin seedlings as needed. Direct sowing avoids the potential transplant shock, but you'll need to protect young seedlings from slugs, which are abundant in our wet springs.

Mustard greens need consistent moisture to thrive, but avoid overwatering, which can lead to disease issues in our climate. Aim to keep the soil consistently moist, but not soggy.

During our typically dry summer months, you'll likely need to water deeply about 1-2 times per week, providing about 1 inch of water each time. Use the finger test: stick your finger about 2 inches into the soil, and if it feels dry, it's time to water. During the wetter spring and fall, you may need to water less frequently.

Water at the base of the plants to avoid wetting the leaves, which can encourage fungal diseases in our humid conditions. Signs of underwatering include wilting leaves and slow growth, while yellowing leaves and mushy stems can indicate overwatering. A layer of mulch, like straw or wood chips, can help retain moisture and suppress weeds, which is helpful in our climate.

You can expect your first harvest of mustard greens in late April through early November, 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 younger leaves will have a milder flavor.

Harvest individual leaves from the outer part of the plant, leaving the inner leaves to continue growing. This cut-and-come-again method encourages continuous production throughout the season. As the first frost approaches in late October, you can cover your plants with a row cover to extend the harvest a bit longer.

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. You might see small, dark beetles that jump when disturbed.
• What causes it: These small jumping beetles feed on leaves, and are most damaging to small, young plants. They thrive in the dry conditions of our mild summers.
• How to fix/prevent it: Use row covers to protect seedlings. Delay planting until plants are larger and more resilient. Kaolin clay can act as a barrier. Neem oil spray can also help. Interplant with basil or catnip to deter 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: These sap-sucking insects reproduce rapidly, especially in warm weather. Ants may farm them for honeydew, exacerbating the problem.
• How to fix/prevent it: Knock them off with a strong water spray. Encourage ladybugs and lacewings, which are natural predators. Insecticidal soap can be used for heavy infestations. Avoid excess nitrogen fertilizer.

Cabbage Worms

• What it looks like: Smooth green caterpillars on brassica leaves. Irregular holes chewed in leaves, and dark green droppings. You might see white cabbage butterflies hovering around plants.
• What causes it: These are the larvae of white cabbage butterflies. They can have multiple generations per season if the weather stays mild enough.
• How to fix/prevent it: Bt spray is very effective. Floating row covers can prevent the butterflies from laying eggs. Handpick caterpillars when you see them. Interplant with aromatic herbs like thyme or sage to deter them.

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.
• What causes it: Mustard greens are a cool-season crop and will bolt when temperatures rise. This is triggered by extended warm temperatures, especially 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. Mulch to keep the soil cool. Harvest before bolting progresses too far.

Pacific Northwest Specific Challenges: Our mild heat and dry-summer rainfall mean that flea beetles and aphids can be persistent problems, especially during the summer months. Late blight isn't a direct threat to mustard greens themselves, but it can affect other plants in your garden, so be mindful of overall garden health. Slugs can be an issue for young seedlings, particularly in our wet springs.

Companion planting can help your mustard greens thrive. Onions and garlic are good companions because their strong scent deters pests like aphids and flea beetles. Beets are also beneficial, as they help improve soil structure and nutrient availability. Dill attracts beneficial insects like ladybugs and lacewings, which prey on aphids. Lettuce can act as a ground cover, helping to retain moisture and suppress weeds.

Avoid planting mustard greens near strawberries or tomatoes. Strawberries are susceptible to similar fungal diseases, and planting them near mustard greens can increase the risk of spreading these diseases. Tomatoes compete for similar nutrients in the soil, potentially stunting the growth of both plants.