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Overview.
Radicchio is primarily a fall and winter crop, native to the Veneto region in northern Italy. It is botanically a biennial plant with bolting triggered by long/lengthening days so spring sown plantings rarely produce the desired shape for each type and often end up with a significant amount of bolting. Furthermore, it is the cool temperatures and overnight frosts of fall that bring out the tenderness and sweetness that balances the bitter notes. Its ideal conditions are a temperate climate with a gradual transition to the cool days and frosty nights of fall. You can certainly have success in places with rapid harsh transitions, but its often best to focus on the earlier maturing strains in those places for the best success. Warmer climates, that don’t achieve cool enough temps in the fall and winter, can produce aesthetically attractive crops but they tend to be more bitter as they do not experience the sweetening effects of frosty nights around harvest.
For growers looking to have successions of harvests in the fall, this can be achieved to some extent by multiple staggered plantings (just as you would plant green beans every couple weeks for a continual harvest through the season), but much more commonly in its homeland of the Veneto in Northern Italy, this is achieved with a single, narrowly timed planting of several varieties of the same type with different days to maturity. This is sometimes referred to as “slotting” and, as an example, there are different selections of “Verona” types that mature anywhere from 55 to 120 days. Using these different slotted varieties you can maintain harvests over a couple months from a single sowing of multiple varieties. Latest maturing varieties often provide the greatest reward in terms of size and quality, but also come with the greatest risk of unfavorable weather and severe cold (not to mention the mole pressure gauntlet!) as you move later into the winter. Earlier maturing varieties often offer the greatest flexibility of planting dates as well as reliability of successful harvest.
As radicchio continues to gain popularity here, increasingly, seed with this quality of specificity is becoming available in the US. We are leagues from where we were even 5-10 years ago in terms of the genetics available to North American growers. Our partnership with Smarties Bio, a young northern Italian Seed Breeding company doing this work in the context of organic field systems, represents a leading edge of this work.
Timing and Growing:
Timing of planting is the single most important key to success with the radicchio, and most often where people go wrong. In our area, radicchio is best sown (usually in flats) from right around the summer solstice through the first third of July. Heading varieties (Chioggia, Verona, Treviso precoce, Lusia, Rosa) are better sown towards the earlier part of this window. Looser or more cold tolerant varieties (Gorizia/Isontina, Castelfranco, Treviso Tardivo, Catalogna) or the earliest slotted varieties of the heading types, have more flexibility and can be successfully sown later in the window. Grumolo (a late winter/early spring harvested variety) can be sown into August.
Transplant at about four weeks into light to moderately fertilized beds . We will often use the earlier part of the season to grow a cover crop of clover or favas to be turned into the soil in preparation for late-July transplant season. If radicchio becomes a larger and larger part of your garden or farm, a couple nutrients to consider correcting for if deficient, are calcium (if you consistently see tip burn in the leaves) as well as boron. We have had success in both three rows (15” spacing) to a 4’ bed top and single rows on 24” center systems. It really depends on preference for weed cultivation technique and equipment. For most varieties we use 12” between plants in-row.
While we find the crops to generally be healthy, they are very popular with deer and rabbits, and especially voles who can cause a lot of damage from eating the plants’ significant roots. Mildew can be a foliar problem some seasons.
Field Heading Varieties:
The field heading varieties (Chioggia, Treviso Precoce, Variegato di Castelfranco, Variegato di Lusia, Verona, Bianco di Chioggia) can be grown without much fuss as outlined above. Color deepens as plants mature and the days get cooler and shorter. We often judge maturity by giving heads a gentle squeeze to gauge how dense they are as we walk through the patch and harvesting when they have filled out in the centers. Heading radicchio stores exceptionally well in the refrigerator or cold storage, easily for several weeks if kept from drying out.
Puntarelle:
Puntarelle was one of our first obsessions almost a decade ago as we started to fall down the radicchio rabbit-hole and remains one of our favorites and a signature crop of our farm still. Probably most closely associated with Rome, puntarella is the base of a classic Roman winter salad Puntarelle alla Romana dressed with a lemony-garlicy-anchovy dressing.
Puntarelle is unique among radicchios in that it is not the leaves, but the bolting stems of the plant that are eaten. It has been bred specially from the toothed leafed Catalogna types to produce a dense head (pigna or “pinecone” in Italian) of many points of bolting stems. The heads are harvested when the individual stems are 4-6” (or longer in some cases). Each stem, which is hollow, is then finely ribboned or pushed through a special tool called a taglia puntarella (a wire grid that matchsticks the stems) and then soaked in cold water. The soak causes the ribbons to curl fancifully. Properly prepared it has a lovely refreshing and succulent crunch with a texture similar to raw asparagus and only a very mild bitterness. It is one of the greatest delicacies the radicchio family has to offer.
In the field it is grown similarly to the heading varieties. Usually beginning in October the pigna start to develop. The harvest window is narrower than many of the other types with prime harvest being from mid October to mid-November. An unfortunately timed stretch of extreme cold can do significant damage during heading.
Pink is the New Red:
The pink varieties, collectively known as “Rosa di Veneto” are relative newcomers to the radicchio family and are playing a large part in radicchio’s newfound popularity in capturing the imaginations of the culinary world and press in North America. They are incomparably beautiful and such a different and unique hue of salad color than anything previously available. As a type they are not grown differently than the heading types as outlined above. However, it is notable for the grower that they are very slow to develop their color. Home gardeners will often think they are doing something wrong or have received the wrong seed as the plants are entirely green for over 3 months of their growing cycle. They are a late maturing type, harvested here in the PNW mainly in December and January, and the color only begins to develop in the final month of growth, often hidden beneath the outer green leaves. These, being bred and developed more recently than the other types, still tend to show a bit more variability in color and form than the others with color ranging from bubblegum pink to a delicate salmon and forms from dense compact heads to looser more open affairs. “Mantavano” reflects an earlier wilder diversity of genetics of this type, while “Rosato” represents work toward a more refined and uniform selection. They are all, however, uniformly attention grabbing.
Forcing Varieties:
So lets take some time to explore the “forcing” varieties as their production requires a little more nuance than the field heading ones.
While “forced” radicchio is considered among the most prized high end categories of radicchio, historically this form was a humble food produced to provide leafy greens in the lean winter months. Forcing is the process where plants are dug and removed from the field (usually in the late fall and winter) to grow a secondary-type growth in a more controlled, warmer, and protected environment- often in complete darkness. The primary types this is most commonly done with are Belgian Endive, Treviso Tardivo, and Goriziana/Rosa Isontina. While I am tempted to call these “graduate level” projects, they simply require more planning and attentiveness than they do any special skill or equipment or anything, at least on a small scale..
First some forcing “theory”: C. intybus (the radicchio family) is as we mentioned biennial and biennial vegetables often employ a couple tricks as strategies to survive the winter in order to produce seed the following year. One is to produce a significant tap root to store energy safely below the ground which it then sends back up to the growing tip in spring when it is safe to produce tender new leaf growth again (think carrots and other root crops), or they very tightly wrap the growing tip above ground with a dense layer of leaves to protect it against the winter elements as it lays vegetatively dormant in the field (think cabbage). Most of the forcing varieties (Belgian endive, Treviso Tardivo, Goriziana/Rosa isontina) go the former route, producing a large tap root. Direct seeding produces a superior root for forcing, but because of the high value of good radicchio seed and due to cultivation preferences it is often impractical to direct seed. In the late fall, leaf growth slows as the plant begins to enter winter dormancy and the energy becomes concentrated in the roots. When you dig plants and bring them into a protected and warmer environment, you are essentially tricking them into thinking its spring and time to start growing leaves again. It is this very tender growth that can be the pinnacle of radicchio deliciousness.
Belgian Endive- The radicchio coolio crowd gives Belgian no love but honestly, if you gave it a cool Italian sounding name like “golden torpedo of Verona” it’d be all over their instagram feeds. Personally, I’d happily argue all day that Belgian endive is just a disenfranchised radicchio, and likely the most commercially successful forced vegetable in North American produce markets. In the field it looks like a wild, over grown dandelion, but starting in October the roots (which look like giant parsnips) are dug and the leaves trimmed back closely (being careful not to nick off the apical meristem-the growing tip in the very center of the leaves). They are then are placed in a dark room, densely packed in bins of circulating water or tubs of damp medium like sand or peat with just the crowns exposed, and over the next 4 weeks the familiar golden “chicons” grow from the trimmed crown. Complete darkness is critical to avoid greening and increased bitterness. We have found success in closets, kitchen cabinets, barns, basements, root cellar... We even grew a commercial crop when we were younger farmers in the crawlspace under the house at a mother-in-law rental in town. One of the beautiful things about Belgian endive is that the roots are so substantial that once trimmed they can be stored in refrigeration (which slows leaf growth to a standstill) for months and removed every so often to start a new round of forcing.
Treviso Tardivo- These are progenitor of most modern heading types of Radicchio. In this field, these grow plants with loose rosettes of very long slender leaves. The forced growth is the famous “squid”, deep red slender leaves with succulent white midribs that curl fancifully inward toward the tip to form loose “heads”. While the plant will naturally replicate this process if simply left in the field, in our opinion there is no quality comparison between the indoor forced product and that of “field-forced”. Forcing yields a larger head of superior quality, especially in terms of tenderness and texture.
We start to look for this secondary growth and deep red coloration in the centers of the plants in the field to indicate that the crop is ready to dig. When ready, we lift plants and shake off as much dirt as possible in the field and stack on a trailer with the leaves still attached. Once plants are removed from the fields, we spray off the roots, pull off only the outermost leaves that are already showing decay, and pack them tightly in containers where the roots will be submerged in water. On a small scale we have done this by packing them in shallow bins, trimming the roots a little if necessary to make sure the crowns are all at a similar height, and filling the container to a couple inches below the tops of the roots. If you have a drain plug that can be helpful for changing the water (I’d recommend draining and refilling with fresh water once or twice per week). On a larger scale plants can be packed in plastic milk type crates or wire totes and placed in a shallow lagoon of water. We have made a simple version of this using a pondliner or water impermeable tarp set in a shallow wood frame and filled with water. More professional systems often use large metal or concrete basins with circulating water. Again, it’s good to drain or pump out and refresh the water a couple times during the growing cycle. Darkness during this phase is helpful but not necessary as if the plants are packed in tightly, the cores still blanch nicely. We have set up lagoons in our winter greenhouse under a shade cloth. A garage or barn can work very nicely. 45-55F/7-12C is a good temperature range to shoot for, and expect that there will invariably be some slime and decay in the outer leaves at harvest time to clean off. Good air circulation is fairly important to reduce this but for me, part of the charm of the harvest is the emergence of a gloriously pristine core from an exterior of rot and slime. Traditionally about 2” of root is peeled and left attached to the head. Its not just for looks, Its delicious! (and helps keep the head together when halved or quartered and roasted).
Gorizia/Isontina- This type is the famous “Rose of Gorizia” producing stunning rose shaped rosetted usually in tones of pink to deep burgundy, though strains of yellow (“canarino”) and variegated also exist. We generally don’t start forcing Gorizia/Isontina types until December. At this point the plants look quite a bit less vigorous in the field, the outer leaves start to decay a bit, and the energy is very much focused in the center of the rosette. At this point we will lift plants, shake off the roots, and pull off all but the very small center-most leaves. Gorizia must be forced in darkness. We do ours with in a medium of damp sand mixed with coco coir, though it can also be done in damp wood shavings, or even packed in totes in water like Treviso. Air circulation is helpful so closing them in a bin with a lid on it to achieve darkness isn’t the best strategy. Root cellars, dark closets, dark basements are all great places. 60F or under is best.
Culinary
I frankly don’t know why we have to stage a “radicchio revolution”, like, honestly who needs to be sold on this stuff? But here we are.
I often hear that bitter is a “challenging” flavor for the American palate. Cool. Ill take that chocolate bar from you. And your coffee. And while I don’t much care for them, it sure looks like IPA’s (which are bitter as can be) seem to have a stranglehold on the craft beer market. If you only have a total of 5 taste perceptions, you can’t just write one of them off!! Of course it makes sense that people like bitter to differing degrees but that just determines how you think about preparing them in the kitchen. As with chocolate, while bitter lovers might gravitate to the darker 70 or even 80% bars, the bitter-shy might prefer it balanced with some sweet or both sweet and fat (milk). While the bitter lover might enjoy a halved roasted head of verona drizzled in olive oil and sitting atop a pile of polenta, the bitter-shy might prefer a milder Gorizia tossed with goat cheese (fat), blood oranges (sweet/tart) and balsalmic (sweet/tart).
There are many ways to cook with radicchio. In our home, we often roast them in the oven, sauté in olive oil, braise, grill, or just shred raw. For raw we consider the forced varieties along with Castelfranco, Lusia, Sugarloaf, and Puntarelle to be the best. Most of the red heading varieties (Verona, Treviso, Chioggia) we prefer cooked, though they can also certainly be eaten in raw preparations. Its good to remember here that frosts in the fall help sweeten especially the midribs of the heading varieties and render them much more naturally balanced flavor-wise. This is why late fall and winter is the big event for this family. In a way, it is a shame that most peoples introduction to the family in the US was through raw, shredded Chioggia grown in warm climate California, and mixed into baby lettuce mixes- less than ideal all around.
When you prefer bitter to be an accent note rather than the main event its good to consider pairing it in the dish with elements of fat and sweet and, of course, salt. As with my chocolate example above, you can think of milk (fat) and sugar (sweet) mixed in coffee for people who find black coffee too bitter. Some things we find pair especially well with radicchio to help balance the bitter notes are…
Sweet: Balsalmic vinegar or pomegranate molasses in dressings or marinades, figs, pomegranate seeds, pears, oranges.
Fat: Olive oil, cheese (especially goat) or cultured nut cheese, pine nuts or walnuts, pumpkin seeds.
You get the idea. And don’t forget the salt.