Mustard Greens

Mustard greens (Brassica juncea) are an annual herb in the mustard family. The leaves and flowers are eaten, and all parts are edible when young. Young leaves go into mixed salads, while older leaves are usually cooked as greens. Leaf shape and color vary widely, from flat to curled and from green to red-tinged. Mature plants are listed at 12 to 18 inches (30 to 46 cm) tall and wide. The plant is listed as invasive in some mid-western states, so check local rules before planting.

The flowers are yellow and bloom in summer and fall, and they draw bees.

Sow seeds outdoors about 2 to 3 weeks before the last spring frost. Seed can be sown from early spring to late summer. Mustard can be sown after the soil reaches 40 °F (4 °C).

Plant the seed about ½ inch (1.3 cm) deep. A seed company suggests ¼ to ½ inch (0.6 to 1.3 cm) deep. Seed planted deeper than ½ inch likely will not germinate.

Seeds germinate best at 55 to 65 °F (13 to 18 °C) and emerge in 7 to 10 days. Mustard grows best when temperatures stay at or below 75 °F (24 °C).

For spring, transplants are the preferred planting material, because seeds germinate slowly in cool spring soil. For fall, direct seeding works well in late summer, when the soil is much warmer. For a fall crop, pick early maturing cultivars and plant 50 to 75 days before the expected maturity date.

Watering. Water regularly to keep the soil uniformly moist, since moisture swings make leaves tough and add off-flavors. Watering early in the day lets the leaves dry before night, which lowers the chance of fungal disease.

Feeding. Apply about ½ cup of nitrogen fertilizer (21-0-0) per 10 feet (3 m) of row, 4 weeks after transplanting or thinning.

Weeds and thinning. Mustard does not compete well with weeds, so control them early. Thin the stand when plants have three to four true leaves. Mulch with grass clippings, straw or shredded newspaper to help control weeds.

Heat and uneven moisture are the main quality problems. Growing mustard above 75 °F (24 °C) causes a bitter flavor. Spring plantings may bolt as the weather warms. Moisture and temperature stress lead to a spicier, unpleasantly strong flavor.

Insects that affect this plant include flea beetles, caterpillars, aphids, slugs and snails. Flea beetles feed on seedlings, and they can reduce plant stands or kill seedlings.

The main disease issues of greens include leaf spots, bacterial blight, black rot and crown and root rots. ‘Carolina Broadleaf’ is described as one of the few bacterial blight resistant cultivars.

Harvest when the leaves reach full size, and before the seed stalk forms. Pick the outer leaves and leave the center to keep growing. Older leaves are often stripped first so the young leaves keep growing. If the growing point is not damaged, all leaves can be cut off to within 2 inches (5 cm) of the soil.

Harvested leaves can be stored in the fridge for 3 to 5 days. Eating greens within a week and storing them in a plastic bag in the refrigerator is advised. Mustard can also be stored for 1 to 2 weeks at 32 °F (0 °C) and 95% relative humidity.

Mustard is listed as a problem for horses. The pages used here do not say which part of the plant or how much is a risk, so keep horses away from plantings and harvested leaves until a clearer source is added.