The radicchio is a particular variety of chicory highly appreciated for its organoleptic qualities. It is a plant with an ancient history. The Italian region that has specialized the most in this cultivar is Veneto. In fact, most of the cultivated varieties, such as red radicchio of Treviso, derive from it, like red radicchio of Chioggia or the variegated Castelfranco radicchio. All these varieties have received the recognition of IGP, protected geographical indication, and must be cultivated according to specific guidelines. This includes, above all, the requirement of geographical origin.
However, radicchio remains a vegetable whose cultivation is within reach for everyone and can provide great satisfaction in a home garden. To start growing it, all you need to do is obtain young seedlings or seeds of your preferred varieties from the best nurseries. Let’s now get to know this valuable vegetable better, the typical Veneto varieties, and the techniques of organic cultivation.
Radicchio (Cichorium intybus) is a leafy vegetable with green, variegated, or red leaves, belonging to the family Asteraceae or Compositae, genus Cichorium. Other plants widely cultivated in our country also belong to this genus, such as endive, smooth escarole, and curly escarole. It is a vegetable species derived from wild chicory plants, which, through human selection, have given rise to the varieties cultivated today.
Varieties of Radicchio
Radicchio plants usually form heads composed of leaves gathered in more or less compact rosettes. They have different sizes, colors, and appearances depending on the variety. The leaves can vary in shape (round, elongated, smooth-edged, serrated-edged) and color (light green, dark green, various shades of red, variegated).
Red Radicchio of Treviso
The red radicchio of Treviso (or Trevigiano) can be considered the variety from which all others have been derived through selection and crosses. There are currently two types of this radicchio: the late and the early.
The late variety of Treviso radicchio is characterized primarily by swollen and fleshy roots, highly appreciated in cooking. The leaves, with their typical red color, are lanceolate, rather narrow, elongated, and upright in growth. They have a fleshy and crunchy rib, which is quite large in proportion to the development of the leaf blade. Due to its shape, this radicchio is also called the big sword. It has a distinctive bitter taste and a very inviting appearance. It is highly resistant to cold and is harvested in the midst of winter.
The early radicchio of Treviso is a variety less resistant to cold. It is harvested before winter arrives. It has wider and less thick leaves than the late variety, with an intense red color. The head is compact and elongated.
Variegated Radicchio of Castelfranco
The variegated radicchio of Castelfranco comes from the hybridization between the red Treviso radicchio and the endive escarole (Cichorium endivia). It has retained the open shape and fringed leaf margin of the endive. The leaves have a slight blistering and a very distinctive color, hence the name “variegated”. In autumn, they are covered with red speckles of varying intensity, which become ivory-cream on the background. These characteristics have earned it the names of edible flower and orchid salad. Its tender texture and slightly bitter taste make it highly regarded by chefs. The plant is of medium-late maturity and is harvested at the beginning of winter.
Red Radicchio of Chioggia
The red radicchio of Chioggia is the most cultivated and consumed variety in Italy. It derives from the variegated Castelfranco radicchio and was selected between the 1930s and 1950s to achieve a more pronounced red coloration. One of its distinctive features is its ability to be cultivated all year round, even in areas different from its place of origin. Once mature, the plants have a well-closed head consisting of rounded, shell-shaped leaves. The edge is smooth, and the rib is white, broadening at the base. The leaves surrounding the central head are of intense green color, with reddish or purplish shades. By removing the outer leaves, the central head remains, of excellent size, with its characteristic deep red color.
Cultivation of Radicchio
Radicchio requires specific cultural care: moderate organic fertilization, periodic shallow soil cultivation or mulching, attentive irrigation. There is also a particular technique called “blanching”, which aims to improve both the taste and appearance of the heads.
As we have seen, radicchio is mainly cultivated in Veneto, indicating that it is a cold-adapted plant. Its cultivation takes place in autumn, although some varieties, like the red radicchio of Chioggia, can be grown all year round.
Soil and Organic Fertilization
Radicchio is a hardy plant that prefers well-cultivated (especially surface) soils, cool, deep, and not compact. Thus, careful soil preparation is necessary, with special refinement before sowing or transplanting. Organic fertilization should be moderate. Ideally, choose portions of soil that have been well-fertilized with mature compost in the previous crop, such as zucchini or tomatoes. If the soil has not been fertilized previously, a lighter fertilization can be chosen before cultivation begins, using home compost or worm humus (which you can purchase here).
Direct Sowing or Transplanting
The cultivation of radicchio can be initiated either by direct sowing in the open field or by using seedlings in soil blocks.
Direct sowing is done using techniques of continuous rows or post-holing. Subsequently, the seedlings are thinned, leaving a spacing of at least 20 cm between each plant. This optimal distance ensures vigorous growth. Transplanting small plants with soil blocks is easier and can be done directly. These seedlings can be self-produced using polystyrene seedbeds or purchased from nurseries. In the former case, it’s important to avoid aging the seedlings in containers and plant them as soon as the roots are well-formed. Transplanting allows for an optimized investment and greater production uniformity. The period for direct sowing is summer, while transplanting is done from September to October. For the cultivation of spring varieties, direct sowing can be done under a tunnel in February. Transplanting, in this case, is done in March, with the beginning of spring.
Radicchio requires constant irrigation. However, care must be taken not to overwater and cause waterlogging. Since the plant remains in contact with the soil for a long time, root rot is one of the most common problems that can occur. Therefore, keep the soil consistently moist but not waterlogged. To ensure consistent water supply, using a drip irrigation system is recommended.
Cultural Care for Radicchio
Weeding and Hoeing
Among the cultural practices required for radicchio, weeding is of particular importance. This involves periodic removal of weeds, accompanied by light hoeing. Hoeing helps loosen the surface crust of the soil, which might form due to precipitation or repeated irrigations. This improves root aeration and expansion.
As an alternative to weeding and hoeing, mulching can be used. For a cultivar like radicchio, natural straw mulch, biodegradable plastic mulch, or jute mulch can be used. You can find the latter two types here and in this specialized store. Mulching, besides saving you the aforementioned tasks, reduces water needs and limits the occurrence of dangerous rots.
In radicchio cultivation, blanching is a crucial operation, a technique we discussed when talking about celery cultivation.
Blanching improves both the quality of the head, making it more tender and delicately flavored, and its visual appearance.
With this technique, light is partially or entirely removed from the plants. This encourages the development of head leaves using the reserve substances accumulated in the roots. Another benefit is the reduction in chlorophyll production, which limits the production of fibrous parts, making the leaves more tender and appetizing. The simplest way to blanch is by tying the outer leaves using a rubber band or a lightweight cord. Plants should be tied 15-20 days before the expected harvest. This should be done when the leaves are dry, as moisture can condense within the heads, creating conditions for rapid rot development. In commercial radicchio cultivation, there are other blanching techniques beyond what we’ve just described. For example, blanching in piles or on sand, which is done after harvest.
Radicchio can be harvested when the head is well closed. To harvest, the plant is lifted from the ground using a pitchfork or a shovel. After harvest, the leaves around the head should be removed, and the main root should be cleaned, trimming it to about 4 cm.
Pests and Diseases
Radicchio is a plant species that is relatively insensitive to attacks by animal pests but more susceptible to fungal diseases.
It is mainly grown in autumn and winter, making it most vulnerable to attacks by slugs. These can be controlled using homemade traps with beer or with iron phosphate, a product approved for organic farming that you can find here. Regarding diseases, common fungal leaf diseases include downy mildew, powdery mildew, anthracnose, rust, botrytis, and collar rots such as rhizoctonia, pythium, and sclerotinia. To prevent the emergence of these pathologies, keep the soil clean and avoid waterlogging.