Mustard Greens in Zone 5B — Mountain West

Mustard greens offer a spicy kick to your Mountain West garden, adding fresh flavor to salads, stir-fries, and soups. Their quick growth makes them a rewarding crop even in our short season, and the cool nights we get, even in summer, can actually improve their flavor by preventing them from getting too bitter too quickly.

Our high altitude and intense sun mean you need to be mindful, but with proper timing and attention to watering, you can easily grow mustard greens here. Our 149-day growing season is plenty long enough to get multiple harvests, especially if you succession plant.

Starting mustard greens indoors is an option, but direct sowing generally works just as well in our climate, and saves you some effort. If you want a head start, especially for a spring crop, start seeds indoors from late March through mid April, about three weeks before you plan to transplant.

Use seed trays and a good seed-starting mix. Keep them warm (around 70°F) and provide plenty of light – a grow light is best, given our late spring cloud cover. Bottom watering helps prevent damping off, which can be an issue with seedlings.

Transplant your mustard greens outdoors from late April through early June. Before transplanting, harden off your seedlings by gradually exposing them to outdoor conditions for about a week. This helps them adjust to the intense sun and cooler nights we often get, even late in spring.

Space them 6-12 inches apart to allow for good air circulation. Be mindful of late frosts, which can still occur, and be ready to cover your transplants if needed.

Direct sowing mustard greens is easy and effective in our Mountain climate. Sow seeds from early April through early August for a continuous harvest.

Prepare your soil by loosening it and adding compost to improve drainage and fertility. Mustard greens prefer a soil temperature of at least 50°F for good germination. Sow seeds about ¼ inch deep and space them 6-12 inches apart.

Mustard greens need consistent moisture to thrive, especially given our dry climate. Aim to keep the soil evenly moist, but not waterlogged. Drought stress can make the leaves spicier and trigger bolting, neither of which are desirable.

In the spring and fall, when temperatures are cooler, you might only need to water once or twice a week. During the hotter summer months, especially with our intense sun, you might need to water every other day, or even daily. Stick your finger about 2 inches deep into the soil – if it feels dry, it's time to water. Generally, give them about 1 inch of water per week, adjusting based on rainfall and temperature.

Water at the base of the plants to avoid wetting the leaves, which can lead to fungal problems, although our low humidity reduces that risk. Signs of underwatering include wilting and yellowing leaves. Overwatering can lead to root rot, indicated by limp, brown leaves. Mulching around your plants with straw or wood chips helps retain moisture and keep the soil cool.

You can expect your first harvest of mustard greens from late May through early October, depending on when you planted. Mustard greens are ready to harvest about 45 days after planting.

Harvest young leaves for a milder flavor, or wait until the leaves are larger for a spicier kick. Pick leaves before the plant starts to flower, as bolting makes the leaves bitter. To harvest, simply snip off the outer leaves with scissors or a knife, leaving the inner leaves to continue growing.

This cut-and-come-again method allows for continuous harvesting throughout the season. As the first frost approaches in early October, harvest all remaining leaves to enjoy before the cold weather sets in.

Here are some common problems you might encounter growing mustard greens 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 that jump when disturbed.
• What causes it: These small jumping beetles feed on the leaves. They're most damaging to small, young plants, and our intense sun can stress the seedlings, making them more vulnerable.
• How to fix/prevent it: Use row covers to protect seedlings during their vulnerable stage. You can also delay planting until the plants are larger and more resistant. Kaolin clay coating can deter them, and neem oil spray can help control infestations.

Aphids

• What it looks like: Clusters of tiny soft-bodied insects (green, black, or white) on stems and leaf undersides. You might also notice sticky honeydew residue and curled or distorted new growth.
• What causes it: These sap-sucking insects reproduce rapidly, especially in warm weather. While our humidity is low, aphids can still thrive, particularly if plants are stressed.
• How to fix/prevent it: A strong water spray can knock them off. Encourage natural predators like ladybugs and lacewings. Insecticidal soap is effective for heavy infestations, and neem oil works systemically.

Cabbage Worms

• What it looks like: Smooth green caterpillars on brassica leaves. You'll see irregular holes chewed in the leaves and dark green droppings. White butterflies hovering around plants are a sign.
• What causes it: These are the larvae of white cabbage butterflies. They can go through multiple generations in a season, even in our climate.
• How to fix/prevent it: Bt spray is very effective. Floating row covers prevent the butterflies from laying eggs on your plants. You can also handpick the caterpillars.

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. Even our moderate-at-altitude summer heat can trigger bolting, especially if combined with dry conditions.
• How to fix/prevent it: Time your plantings for cool weather in spring and fall. Choose bolt-resistant varieties. Provide shade during warm spells with shade cloth. Mulch to keep the soil cool. Harvest your greens before bolting progresses.

Mountain West Specific Challenges: Our dry climate and intense sun mean you really need to stay on top of watering to prevent stress, which can make mustard greens more susceptible to pests and bolting. Hail can also be a concern, so consider using row covers or netting for protection, especially during spring and early summer storms.

Mustard greens benefit from companion planting. Onions and garlic are good companions because their strong scent repels pests like aphids and cabbage moths. Beets are beneficial because they don't compete for the same nutrients and can help loosen the soil. Dill attracts beneficial insects like ladybugs, which prey on aphids. Lettuce provides ground cover, helping to retain moisture and suppress weeds.

Avoid planting mustard greens near strawberries or tomatoes. Strawberries are susceptible to some of the same fungal diseases as mustard greens, and tomatoes can attract pests that also affect mustard greens.