Plant specifications The Black Mustard herb plant has a sturdy stalk with wrinkled, lobed, and dark green leaves. Yellow, 4-petaled flowers appear on spikes in early summer. Both the seed and the greens of this herb plant are used. The greens can be cooked or steamed, but as the summer gets hotter, the greens get stronger with a bitter taste. Black Mustard plants are often grown in two crops during the season to keep a supply of the young greens. Black Mustard seeds come in the summer heat as the plant bolts. The plant size can vary from 24 inches to 72 inches in height, depending on the conditions where it is growing. Start Mustard seeds directly outdoors a couple of weeks before the end of frost season. Prepare a seedbed with lot of organic matter added to the soil and cover the herb seeds with 1/2 inch of soil. * Average Germ Time: 14 - 21 days * Keep moist until germination * Attracts bees and butterflies * Depth: 1/2 inch * Height: 24 - 72 inches * USDA Zones: 4 - 7 * Season: Annual