Mustard Greens in Zone 5B — Northeast

Mustard greens bring a peppery zing to your table, and they're surprisingly easy to grow in our Northeast gardens. They thrive in the cooler temperatures we often experience, especially with our cool nights, and offer a welcome burst of flavor in salads, stir-fries, and more. Plus, they're packed with nutrients, making them a healthy addition to your homegrown bounty.

Our short growing season and the occasional late frost can be a bit of a hurdle, but with careful timing, you can enjoy a continuous harvest of mustard greens. With our 168-day growing season, there's plenty of time to get several crops in, especially if you take advantage of both spring and fall plantings.

Starting mustard greens indoors is an option, though not always necessary given how well they direct sow. However, if you're eager to get a very early start, especially given our late springs, it’s worth considering. Start your seeds indoors mid-March through early April, about three weeks before you plan to transplant them outside.

Use seed trays with a good seed-starting mix and provide warmth (a heat mat is helpful) and plenty of light (grow lights are best). Keep the soil consistently moist, and consider bottom watering to avoid damping off. This is particularly useful in our humid climate, as it prevents excess moisture on the leaves.

Transplant your mustard greens seedlings outdoors mid-April through late May, once the danger of hard frost has passed. 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 common in our Northeast springs.

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

Direct sowing mustard greens is a great way to get a quick and easy harvest. Sow seeds late March through mid August for succession planting. This ensures a continuous supply of fresh greens throughout the growing season.

Prepare your soil by loosening it and removing any rocks (we all know about our rocky New England soil!). Mustard greens prefer soil temperatures above 45°F for optimal germination. Sow seeds about ½ inch deep and space them 6-12 inches apart. Thin seedlings as needed once they emerge.

Mustard greens need consistent moisture to thrive, but overwatering can be just as detrimental. In our Northeast climate, with its moderate humidity and even rainfall, it's crucial to strike the right balance. During the spring and fall, when temperatures are cooler and rainfall is more frequent, you may only need to supplement natural rainfall once or twice a week. In the warmer summer months, especially if we experience a dry spell, you might need to water more frequently.

Use the "finger test" – stick your finger about 2 inches deep into the soil. If it feels dry, it's time to water. 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 moderately humid environment.

Signs of underwatering include wilting leaves and slow growth. Overwatering can lead to yellowing leaves and root rot. A layer of mulch, like straw or shredded leaves, can help retain moisture in the soil and suppress weeds, which is especially helpful in our climate where weeds can thrive.

You can expect your first harvest of mustard greens mid May through mid October, about 45 days after planting. For a milder flavor, harvest the young, tender leaves. Larger, more mature leaves will have a spicier, more pungent taste. It's best to harvest before the plant starts to flower, as bolting can make the leaves bitter.

To harvest, simply snip off the outer leaves with scissors or a knife, leaving the inner leaves to continue growing. This allows for a continuous harvest throughout the season. As our first frost approaches in early October, you can extend your harvest by covering the plants with a cold frame or row cover. This will protect them from the frost and allow you to enjoy fresh mustard greens for a little longer.

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

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: Flea beetles are small jumping beetles that feed on leaves. They are most damaging to small, young plants and can be more prevalent during dry spells.
• How to fix/prevent it: Row covers are your best bet for protecting seedlings. You can also delay planting until plants are larger and more resilient. Kaolin clay can provide a protective coating. Neem oil spray can also help. Interplanting with basil or catnip may deter them. Healthy, vigorous 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. You might notice a sticky honeydew residue or curled and distorted new growth.
• What causes it: Aphids are sap-sucking insects that reproduce rapidly, especially in warm weather. Ant colonies may farm them for honeydew.
• How to fix/prevent it: A strong spray of water can knock them off. Encourage beneficial insects like ladybugs and lacewings. Insecticidal soap is effective for heavy infestations. Neem oil works systemically. Avoid excess nitrogen fertilizer, which attracts them.

Cabbage Worms

• What it looks like: Smooth green caterpillars on brassica leaves. Irregular holes chewed in leaves and dark green droppings are common. You might see white butterflies hovering around your plants.
• What causes it: These are the larvae of cabbage white butterflies. They can have multiple generations per season in warm climates.
• How to fix/prevent it: Bt spray is very effective. Floating row covers prevent the butterflies from laying eggs. Handpick caterpillars whenever you see them. Interplant with aromatic herbs like thyme and sage. Encourage parasitic wasps.

Bolting in Heat

• What it looks like: The plant sends up a flower stalk. The leaves become tough and bitter, and the overall harvest quality declines.
• What causes it: Mustard greens are cool-season crops, and they bolt when temperatures rise consistently above their comfort zone.
• 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 promptly before bolting progresses too far.

Northeast Specific Challenges: Our moderate heat and moderate-to-humid humidity can create conditions that favor some pests and diseases. The key is to monitor your plants regularly and take action early. Our even rainfall is a blessing, but be mindful of overwatering, especially in heavy clay soils.

Good companions for mustard greens include onions and garlic, as their strong scent can help deter pests. Beets are also a good choice, as they don't compete for the same nutrients. Dill attracts beneficial insects that prey on aphids and other pests. Lettuce can provide ground cover, helping to keep the soil cool and moist.

Avoid planting mustard greens near strawberries or tomatoes. Strawberries can be susceptible to the same pests and diseases, and tomatoes can inhibit the growth of mustard greens.