Mustard Greens in Zone 4B — Mountain West

Mustard greens are a fantastic addition to any Mountain West garden. Their peppery bite adds a unique flavor to salads, stir-fries, and soups, and they thrive in our cool nights and intense sunlight. Plus, the quick growth cycle means you can enjoy fresh greens even with our short growing season.

Our high altitude and intense sun can be challenging, but with careful timing, you can easily grow mustard greens. Our 128-day growing season is just right for multiple harvests if you plan accordingly.

Starting mustard greens indoors isn't always necessary, but it can give you a head start, especially if the spring is late. Sow seeds indoors early to late April, about 3 weeks before you intend to transplant them.

Use seed trays with a good seed-starting mix, and keep them in a warm spot with plenty of light – a south-facing window or grow lights work well. Bottom watering is a great way to keep the soil consistently moist without damping off. Remember our spring weather often has temperature swings, so starting indoors offers more control.

Transplant your mustard greens seedlings outdoors early May through mid June, once the risk of hard frost has passed. Before transplanting, harden off your seedlings by gradually exposing them to outdoor conditions for about a week.

Space them 6-12 inches apart in your garden bed. Keep an eye on the weather forecast; even in May and June, we can get unexpected cold snaps here in the mountains, so be prepared to cover them if needed.

Direct sowing is a great option for mustard greens, and it's my preferred method! Sow seeds mid April through late July for a continuous harvest.

Prepare your soil by loosening it and adding compost. Mustard greens prefer a soil temperature of at least 50°F for germination. Plant seeds 1/4 inch deep and space them 6-12 inches apart. Direct sowing avoids transplant shock, but be aware that young seedlings are more vulnerable to flea beetles.

Consistent moisture is key for happy mustard greens in our dry Mountain West climate. While they aren't drought-tolerant, overwatering can be just as harmful.

In the spring, when temperatures are cooler, water deeply once or twice a week, providing about 1 inch of water each time. As summer heats up (to our moderate-at-altitude highs), increase watering to 2-3 times a week, ensuring the soil stays consistently moist but not waterlogged. Use the finger test: 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 to avoid wetting the leaves, which can minimize potential fungal issues in our low-humidity environment.

Yellowing leaves can indicate overwatering, while wilting and increased spiciness signal underwatering. Mulching around your mustard greens with straw or wood chips helps retain moisture and regulate soil temperature, which is especially helpful during our intense summer sun.

You can expect your first harvest of mustard greens early June through late September, about 45 days after planting. Young leaves are tender and have a milder flavor, while larger leaves become spicier.

Harvest by snipping off the outer leaves, leaving the inner leaves to continue growing. This allows for continuous production throughout the season. To encourage continued production, remove any flower stalks as soon as they appear. As our first frost approaches in mid- September, harvest any remaining leaves to enjoy before the cold sets in.

Mustard greens, like all garden plants, can face challenges. Here are some common problems we see in the Mountain West:

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 love to feed on brassicas. They're most damaging to small, young plants.
• How to fix/prevent it: Row covers are your best friend for protecting seedlings. You can also delay planting until plants are larger and more resilient. Kaolin clay can create a protective barrier, and neem oil spray can help control infestations.

Aphids

• What it looks like: Clusters of tiny green, black, or white insects on stems and leaf undersides. You might also notice sticky honeydew residue and curled or distorted new growth.
• What causes it: Aphids are sap-sucking insects that reproduce rapidly, especially in warm weather.
• How to fix/prevent it: A strong spray of water can knock them off. Encourage natural predators like ladybugs and lacewings. Insecticidal soap is effective for heavy infestations, and neem oil works systemically. Avoid over-fertilizing with nitrogen, as it attracts aphids.

Cabbage Worms

• What it looks like: Smooth green caterpillars chewing irregular holes in the leaves. You might also see dark green droppings and white butterflies fluttering around your plants.
• What causes it: These are the larvae of those white cabbage butterflies.
• How to fix/prevent it: Bt spray is very effective against cabbage worms. Floating row covers will prevent the butterflies from laying eggs. Handpick any caterpillars you find and 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.
• What causes it: Mustard greens are a cool-season crop and will bolt when temperatures rise consistently above 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 and mulch to keep the soil cool. Harvest your greens before bolting progresses too far.

Mountain West Specific Challenges: Our intense sun and dry air can exacerbate these problems. Consistent watering and providing some afternoon shade during the hottest part of the summer can help prevent bolting and keep your mustard greens healthy. Also, be vigilant about checking for pests, as they can multiply quickly in our climate.

Companion planting can greatly benefit your mustard greens in the Mountain West. Onions and garlic are excellent companions because their strong scent deters many pests. Beets also make good neighbors, as they don't compete for the same nutrients. Dill attracts beneficial insects that prey on aphids and other pests. Lettuce provides ground cover, helping to retain moisture in our dry climate.

Avoid planting mustard greens near strawberries or tomatoes. Strawberries are susceptible to verticillium wilt, which can also affect mustard greens. Tomatoes can compete for the same nutrients, hindering the growth of both plants.