Gardeners who enjoy a variety of greens often include mustard in home gardens because these tasty green leaves fit deliciously into many savory recipes. Because mustard is a cool-season crop, you must plant it in early spring or late summer to allow it to grow while daily temperatures are below 75 F. Once you plant mustard seeds, they will emerge from the soil and quickly grow into large, leafy greens fit for harvesting.
Prepare a sunny growing area in early spring when the soil temperature rises above 40 F (approximately three weeks prior to the final spring frost). Work the garden soil with the spade to a depth of approximately 6 inches. Add 3 inches of compost to the top of the soil and add 4 cups of fertilizer (10-10-10) over the soil for every 100 square feet of growing space. Work these amendments into the soil well with the garden spade. Smooth the top of the soil with the rake to finish preparing the garden area.
Create rows for the mustard seeds with 1-foot spacing between the rows. Space the seeds 3 inches apart in the prepared rows and cover the seeds with a half-inch of soil. Water the newly planted mustard seeds generously immediately after you finish planting them. Keep the soil evenly moist while the seeds germinate.
Thin the mustard seedlings when they have at least three true leaves, pulling the weakest plants to leave the seedlings approximately 5 inches apart.
Apply 2 inches of mulch around the mustard seedlings to help keep the soil evenly moist and to keep weeds from growing near the seedlings.
Sprinkle approximately a half-cup of fertilizer (21-0-0) along each 10 feet of row to fertilize the mustard seedlings about one month after thinning them. Keep the fertilizer granules about 3 inches away from the seedlings and work the fertilizer into the soil with the hand rake. Water the soil well immediately after fertilizing to help the fertilizer get absorbed down to the seedling roots.
Harvest mustard greens when the leaves are about 3 to 4 inches long by clipping the leaves off at the base of the stems with scissors. Allow the mustard plants to continue growing and you can continue to harvest leaves as they mature. A mustard plant will go on producing viable leaves even after nightly temperatures drop down to freezing.