Mustard Greens in Zone 3A — Great Plains

Mustard greens bring a peppery zing to salads and stir-fries, and they're surprisingly easy to grow here in the Plains. Their quick maturity makes them perfect for squeezing in a spring or fall crop, even with our shorter growing season. Plus, that robust flavor stands up well to the intense sunshine and fertile prairie soil we're known for.

Now, we all know the Plains throws its fair share of curveballs – from late frosts to early heat waves and the occasional hail risk. But with a little planning, and by timing your plantings strategically within our roughly 108-day growing season, you can absolutely enjoy a bountiful harvest of mustard greens.

Starting mustard greens indoors is an option, but honestly, it's usually not necessary unless you're itching for a super early start. If you want to get a jump on the season, start seeds indoors from mid-April through early May, about 3 weeks before you plan to transplant.

Use seed trays with a good seed-starting mix, and keep them warm (around 70°F) until germination. Bottom watering helps prevent damping off. Place under grow lights or in a very sunny window. Just remember, our spring weather can be unpredictable, so be prepared to protect those tender seedlings if a late cold snap hits.

Transplant your mustard green seedlings outdoors from mid-May through late June, once the risk 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 wind and temperature swings we often experience.

Space the plants 6-12 inches apart to allow for good air circulation. Keep an eye on the forecast – a late hail event could decimate young plants, so consider using row covers if there's a risk.

Direct sowing is the most common and often easiest way to grow mustard greens in the Plains. Sow seeds directly into the garden from late April through mid-July. Make sure the soil is well-worked and has warmed up a bit.

Plant seeds about ¼ inch deep, spacing them 6-12 inches apart, or sow them closer together and thin later. Direct sowing is simple, but you'll need to stay on top of weeding and ensure consistent moisture, especially during germination.

Mustard greens need consistent moisture to thrive, but they definitely don't like soggy feet. Aim to keep the soil evenly moist, especially during hot, dry spells.

In the spring and early summer, when rainfall is more frequent, check the soil moisture every few days using the finger test: stick your finger about 2 inches into the soil. If it feels dry, it's time to water. During the hotter months, you might need to water every other day, providing about 1 inch of water per week. Water at the base of the plants to avoid wetting the leaves, which can encourage fungal diseases in our low-to-moderate humidity.

Signs of underwatering include wilting leaves and slow growth. Overwatering can lead to yellowing leaves and root rot. A layer of organic mulch, like straw or shredded leaves, will help retain moisture and regulate soil temperature, a real benefit when dealing with our extreme temperature swings.

You can expect your first harvest of mustard greens from mid-June through mid-September, about 45 days after planting. The key is to harvest young leaves for a milder flavor, or let them grow larger for a spicier kick.

Pick the outer leaves as needed, leaving the inner leaves to continue growing. This encourages continuous production throughout the season. Be sure to harvest before the plants start to flower (bolt), as the leaves will become bitter.

As the first frost approaches in early September, harvest any remaining leaves. Mustard greens can tolerate a light frost, but a hard freeze will damage them. You can also cover them with a frost blanket to extend the harvest a little longer.

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

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 that haven't had time to establish.
• How to fix/prevent it: Row covers are your best friend for protecting seedlings during that vulnerable stage. You can also delay planting until the plants are larger and more resilient. Kaolin clay can be sprayed on the leaves as a deterrent, and neem oil can also help.

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 and curled or distorted new growth.
• What causes it: Aphids are sap-sucking insects that reproduce rapidly, especially in warm weather. Ant colonies sometimes farm them for honeydew.
• How to fix/prevent it: A strong spray of water can knock them off the plants. 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 on the leaves, with irregular holes chewed in them. You might also see dark green droppings and white butterflies fluttering around your plants.
• What causes it: These caterpillars are the larvae of white cabbage butterflies. They can have multiple generations per season if the weather stays warm.
• How to fix/prevent it: Bt spray is very effective against cabbage worms. Floating row covers can prevent the butterflies from laying eggs on your plants. Handpicking caterpillars is also an option.

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 they'll bolt (go to seed) when temperatures rise. This is especially true during our hot Plains summers.
• How to fix/prevent it: Time your plantings for cooler weather in the spring and fall. Choose bolt-resistant varieties if possible. Provide shade during warm spells, and mulch to keep the soil cool. Harvest the leaves before bolting progresses too far.

Great Plains Specific Challenges: Our hot summers, low-to-moderate humidity, and variable rainfall can all impact mustard greens. The heat can cause bolting, while inconsistent moisture can stress the plants and make them more susceptible to pests and diseases. Consistent watering and some afternoon shade during the hottest part of the summer are essential.

Mustard greens play well with some neighbors in the garden. Onions and garlic help deter pests like aphids. Beets are good companions because they don't compete for the same nutrients. Dill attracts beneficial insects that prey on pests, and lettuce provides ground cover to help retain moisture.

Avoid planting mustard greens near strawberries or tomatoes. Strawberries are susceptible to some of the same fungal diseases as mustard greens, and tomatoes can stunt the growth of mustard greens.