This versatile Japanese green is called mustard spinach, spinach mustard, or komatsuna, but it's neither mustard nor spinach! Whatever its name, this delicious, leafy green is milder than other mustards, very easy to grow, and quickly produces flat, smooth, dark, glossy green leaves that can be picked as baby greens or grown to full size. Hardy and productive plants are slow to bolt and tolerate cold, heat, and dry conditions; although best results in cool weather.