Radicchio is a tight ball of purple leaves streaked with white. It is a member of the chicory family and has the typical bitter taste. It is often put in salads at good restaurants and in salad mixes. You'll find it in the grocery store for $4.50 a head, or $4.50 pound.
I started growing radicchio several years ago. I did not pay much attention to it and in winter it formed the heads and I was pleased to be harvesting this expensive vegetable. (I grew padrón peppers, another expensive vegetable, this year to the delight of family, friends, and neighbors—the peppers were selling at one point for $6.50 a quarter pound.)
I have planted radicchio the last four years in a row now. At first I had difficulty getting the seeds to germinate and then for two seasons I got a great profusion of plants and green leaves but no purple balls. I thought there was something wrong with the seeds and I pulled the plants up.
I planted again this year and got the green leaves but I did not pull them up and I am starting to get the purple balls. I only recently came on an article on line that described how to grow radicchio. Turns out radicchio is a perennial and will form the balls again in the spring! I also learned that I should have cut the profusion of leaves down to within two inches from the ground to encourage the formation of the purple balls.
Since discovering that information I have found even more elaborate schemes for growing this expensive vegetable. I suspect that these methods are used in commercial cultivation of radicchio. They are too much work for me, however, at any price.