Radicchio is a leaf chicory (Cichorium intybus, Asteraceae), sometimes known as Italian chicory. It is grown as a leaf vegetable which usually has white-veined red leaves. It has a bitter and spicy taste, which mellows when it is grilled or roasted. It can also be used to add color and zest to salads.
Humans have been using radicchio since ancient times. Pliny the Elder wrote of it in Naturalis Historia, praising its medicinal properties; he claimed it was useful as a blood purifier and an aid for insomniacs. In fact, radicchio contains intybin, a blood and liver tonic, as well as a type of flavonoid called anthocyanins.
Modern cultivation of the plant began in the fifteenth century, in the Veneto region of Italy, but the deep-red radicchio of today was engineered in 1860 by the Belgian agronomist Francesco Van den Borre, who used a technique called imbianchimento (whitening) or preforcing to create the dark red, white-veined leaves. Radicchio plants are taken from the earth and placed in water in darkened sheds, where lack of light and ensuing inhibition of chlorophyll production cause the plants to lose their green pigmentation.
The varieties of radicchio are named after the Italian regions where they originate: the most ubiquitous variety in the United States is radicchio di Chioggia, which is maroon, round, and about the size of a grapefruit. Somewhat less common in the states is the radicchio di Treviso, which resembles a large Belgian endive: other varieties include Tardivo, and the white-colored radicchio di Castelfranco, both of which resemble flowers and are only available in the winter months. In the same way that the parmesan cheese-makers of Parma, Italy have sought to protect the name "parmesan" to signify only cheeses made in their region under the supervision of a regulating body, so too have the radicchio farmers of the Veneto sought to protect the names of some radicchio varieties, including Tardivo.
In Italy, where the vegetable is quite popular, it is usually eaten grilled in olive oil, or mixed into dishes such as risotto: in the United States it is gaining in popularity but is more often eaten raw in salads. As with all chicories, if grown correctly its roots can be used to mix with coffee. It can also be served with pasta, in strudel, as a poultry stuffing, or as part of a tapenade.
Radicchio is easy to grow but performs best in a spring (USDA Zone 8 and above) and fall (everywhere) garden. It prefers more frequent but not deep watering, the amount of water varying based on soil type. Infrequent watering will lead to a more bitter tasting leaf. However, for fall crops the flavor is changed predominantly by the onset of cold weather (the colder the mellower), which also initiates the heading and reddening process in traditional varieties. There are newer, self-heading varieties whose taste is not yet as good as a traditional variety which has matured through several frosts or freezes (E.g., Alouette). Radicchio matures in approximately three months.