Mustard Greens in Zone 7A — Mountain West

Mustard greens are a fantastic addition to your Mountain West garden. Their peppery bite adds a unique flavor to salads, stir-fries, and soups, and they thrive in our cool spring and fall weather. Plus, the intense sunlight we get here seems to concentrate their flavor, making them even more delicious.

Our short growing season and unpredictable spring weather can be a challenge, but with careful timing, you can enjoy multiple harvests of mustard greens. Our 173-day growing season gives you plenty of opportunity to squeeze in a few crops if you plan well.

Starting mustard greens indoors isn't always necessary in our climate, but it can give you a head start, especially for a spring crop. Begin in early to late March, about three weeks before you plan to transplant. Use seed trays or small pots filled with a good seed-starting mix.

Keep the soil consistently moist – bottom watering is a great way to prevent damping off. Place the trays under grow lights or in a very sunny window. Remember our springs are late, so starting indoors buys you precious time.

Transplant your mustard greens seedlings outdoors in early April through mid May, once the soil has warmed up a bit and 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 the plants 6-12 inches apart in well-drained soil. Even though the days warm up quickly here, be prepared for those cool Mountain nights – protect young transplants with row covers if needed.

Direct sowing mustard greens is a simple and effective method, especially for succession planting. Sow seeds directly into the garden from late March through mid August. The soil should be at least 45°F for good germination.

Prepare the soil by loosening it and adding compost. Sow seeds about ½ inch deep and 6-12 inches apart. Direct sowing works best when the weather is consistently cool and moist; be ready to provide supplemental water if it's dry.

Mustard greens need consistent moisture, especially in our dry Mountain climate, but they don't like soggy soil. Aim to keep the soil evenly moist, but not waterlogged. During the heat of the summer, you might need to water every other day.

Stick your finger about 2 inches deep into the soil. If it feels dry, it's time to water. Generally, give your mustard greens 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 reduce the risk of fungal diseases in our low-humidity 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 wood chips, can help retain moisture and keep the soil cool, which is especially helpful as our days get longer and the sun gets more intense.

You can expect your first harvest of mustard greens in early May through mid October, about 45 days after planting. Young leaves are milder and more tender, while larger leaves have a spicier, more robust flavor. Harvest leaves when they are 4-6 inches long.

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. Be sure to harvest before the plant starts to flower, as bolting will make the leaves bitter.

As our first frost approaches in early October, harvest any remaining leaves. You can blanch and freeze them for later use or add them to compost pile.

Here are some common problems you might encounter with mustard greens in our Mountain West gardens:

Flea Beetles

• What it looks like: Tiny round holes (shot-hole pattern) in leaves, especially on young seedlings. You might also see small dark beetles that jump when disturbed.
• What causes it: Flea beetles are small jumping beetles that feed on leaves. They’re particularly damaging to small, young plants. The dry conditions we often experience can stress plants and make them more susceptible.
• How to fix/prevent it: Use row covers to protect seedlings during their vulnerable stage. Delay planting until plants are larger and more resilient. You can also try applying a kaolin clay coating or spraying with neem oil. Interplanting with basil or catnip can help deter them.

Aphids

• What it looks like: Clusters of tiny soft-bodied insects (green, black, or white) on stems and leaf undersides. You might also 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. They can be particularly drawn to plants stressed by our alkaline soil.
• How to fix/prevent it: A strong spray of water can knock them off. Encourage natural predators like ladybugs and lacewings. For heavy infestations, use insecticidal soap or neem oil. Avoid excess nitrogen fertilizer, as it attracts them.

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 your plants are a sign of future problems.
• What causes it: Cabbage worms are the larvae of white cabbage butterflies. They can go through multiple generations in our warm (but not too hot) summers.
• How to fix/prevent it: Bt (Bacillus thuringiensis) spray is very effective. Use floating row covers to prevent the butterflies from laying eggs. Handpick caterpillars when you see them. Interplant with aromatic herbs like thyme or sage to deter the butterflies.

Bolting in Heat

• What it looks like: The plant sends up a flower stalk, and the leaves become tough and bitter. Overall harvest quality declines.
• What causes it: Bolting occurs when cool-season crops are exposed to extended warm temperatures. Mustard greens bolt when days consistently exceed 80°F. Our intense sun and rapid temperature swings can exacerbate this.
• How to fix/prevent it: Time your plantings for cool weather in spring and fall. Choose bolt-resistant varieties. Provide shade during warm spells, especially in the afternoon. Mulch to keep the soil cool. Harvest leaves regularly to encourage continued production and delay bolting.

Mountain West Specific Challenges: Our intense sun and low humidity can stress plants, making them more susceptible to pests and diseases. The dry climate means consistent watering is crucial. Also, keep an eye out for hail, which can shred the leaves. Row covers can offer some protection from both hail and intense UV radiation.

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

Avoid planting mustard greens near strawberries, as they can attract pests that affect both crops. Tomatoes are also not ideal companions, as they prefer slightly acidic soil, while mustard greens prefer a more neutral to slightly alkaline soil, which is common in our region.