Radicchio is a spring or fall green with a sharp, slightly bitter taste. While some gardeners start the seeds indoors for later transplanting, most simply sow the seeds directly into the garden bed. Popular varieties include Red Surprise and Verona Red.
Radicchio likes fertile, well-drained soil in a mostly sunny location. With a garden fork, work some compost or soil conditioner into the top 5" or 6" of soil. Form rows in the garden bed approximately 24" part.
Sprinkle seeds along the rows. It is fine if seeds overlap as the seedlings will be thinned later on. Cover the seeds with 1/4" of fine garden soil and gently water them in. Keep the bed moist until the seeds germinate.
The radicchio seeds should germinate in about a week. When the seedlings are 1" tall, thin them so that the plants are spaced 8" to 15" apart. To remove them, simply snip the plants at the soil line with a pair of scissors.
One of the secrets to growing radicchio is to give it plenty of water. When the plants get drought-stressed, the leaves turn tough and bitter. Add a generous layer of mulch around the base of the plants to cool the roots, prevent weeds and maintain adequate moisture.
If the plants send up a flower stalk instead of forming a head, cut off the stalk near the ground to encourage the formation of a new head.
Radicchio matures in about 80 to 90 days. As soon as the heads are compact, firm and about the size of a baseball, simply cut the plant off at the soil line with a sharp knife. It's best to eat radicchio soon after harvesting it, but it will keep for as long as a week in the refrigerator.