You can direct seed for baby leaves or you can plant 12 inches and let grow. You can harvest the outer leaves but mustards will not hold in the field long.
Mustard greens have broad, wavy frilled leaves with longitudinal veins. Upright leaves are supported by thin pale green stems. Mustard greens have a distinct, succulent, crunchy and yet tender texture. Their flavor is robust with bold peppery nuances.