Pull all weeds and vegetation from the growing area by hand. Remove any rocks or sticks you see from the garden.
Lay down a 3-inch layer of organic matter on top of the planting area. Use a rototiller or garden shovel to mix the organic matter into the top 3 to 4 inches of soil. Organic matter is anything that will break down and add nutrients to the soil.
Press down the soil with a garden hand tamper. This will level and firm the soil in the planting area.
Drag the handle of a garden tool across the planting area to create a trench for the mustard seed. Make the depth of the trench 1 inch deep. Create additional mustard rows 6 inches apart.
Sprinkle the mustard seeds into the trench at a rate of 18 to 27 seeds per square foot.
Cover the mustard seeds with a 1-inch layer of garden soil.
Tamp the soil down with a garden tamper. This will keep the small seeds from washing away in loose soil.