Plant seeds in early spring, preferably in March or April, as mustard seeds grow best in a cool, damp climate. If desired, a second crop of seeds can be planted in early fall.
Plant seeds in rows approximately one foot apart. Sow seeds three inches apart, and 1/4 to 1/3 of an inch deep in the soil.
Check the soil each day. If it is dry, water it until the soil feels moist when touched.
Weed the area every day so that weeds will not consume all of the water and nutrients the mustard seeds need in order to grow.
Harvest when the plant begins to yellow, and before the seedpods split open. Mustard seeds typically germinate within three to 10 days and their plants reach maturity after 45-50 days. Allow the seeds to ripen inside the pod after picking.
Store seeds in an airtight container.