Radicchio is an Italian green from the chicory family that grows best in cool weather. It's slow to bolt but like many of the red or butter lettuces it's not cool enough in Kihei to initiate heading or to turn the leaves red in all varieties.
Indigo is an F1 hybrid that was developed to be adaptable to the summer heat. It is the only round radicchio I've grown that produced a compact head. When planted close together (6 to 8 inches apart)the outer leaves are large enough to naturally self blanch the center heads.
Radicchio is easy to grow in containers and needs a soil depth of at least 6 inches. With the exception of Indigo, I plant radicchio seeds from October through November. Indigo can be planted from September through March with good results. Radicchio needs 3 months from seed to maturity.
One of the best things about growing radicchio is that it's not bothered by any of the destructive Kihei insects like the cabbageworm. It's one of a few salad greens that doesn't need to be covered with a row cover or tulle. However, I recommend using snail bait on the ground around the containers as snails and slugs will eat the outer leaves.