Potherb mustard is an oriental cooking green also known as mizuna, kyona, Japanese greens, and sometimes California peppergrass. It is widely grown in Japan, but is found only occasionally in gardens in the United States.
In appearance, potherb mustard has about the same plant height (12 to 18 inches), color (yellow-green), and texture (smooth and a bit fuzzy) as curly mustard, but the leaf shape is quite different. Leaves of potherb mustard are deeply notched, narrow, feathery, and quite attractive. A single plant may have as many as 180 leaves clustered together in a 12-inch diameter, compact bunch.
In the Florida garden, grow potherb mustard at the same time of the year as other cool season greens are grown: September through March. It withstands frost and light freezes and is not quick to seed even in periods of warm weather that occur during the winter months.
Start potherb mustard by sowing seeds directly in the garden. Sow seeds ½ inch deep in rows spaced 12 to 18 inches apart. Thin the seedlings so that plants stand 6 to 12 inches apart. Use the extra plants as they are thinned, or transplant to other areas of the garden.
Prepare the garden soil much as for other vegetables. Be sure to water frequently. In the garden at Gainesville, when the mustard was grown in the fall and winter, tiny caterpillars devoured the leaves. Nothing but the midribs remained intact.
The leaves of potherb mustard are ready for use any time after 3 weeks of growth. Break off as many leaves as needed, but keep enough young foliage to continue regrowth. If preferred, the entire plant may be harvested at one cutting to make room for planting some other kind of vegetable.
The leaves may be eaten raw, as in a salad. The taste is mild and the ornate leaves make the salad more decorative. As a potherb it is prepared in many ways: as a steamed or boiled well-seasoned green, stir-fried, in soups, or mixed with other vegetables. Like other mustards, potherb mustard is rich in vitamins and minerals.