Radicchio
Radicchio is a bright, purple-red, cool-weather-loving perennial. Like a cabbage, it grows heads that can be chopped up and thrown into a salad, or cooked into pastas, omelettes, and more. Its bitter flavor adds character and color to dishes.
VarietiEs
The most commonly-planted variety of radicchio is Radicchio di Verona, also known as Radicchio Rosso, which grows a cabbage-like head. For longer, spear-shaped radicchio, opt for Radicchio di Treviso. For radicchio connoisseurs, nontraditional varieties include Chioggia and Castelfranco.
WHERE RADICCIO THRIVES
Regional compatibility
Radicchio can be planted nearly anywhere in the United States although it prefers temperate weather. Seeds won't germinate when temperatures climb higher than the mid-70s so it should be planted in spring or fall. In hotter regions, winter is the optimal growing season. Even when it’s cold enough to freeze over, radicchio can be thawed and eaten.
Optimal shade & sun
In cool weather, plant radicchio where it will receive full sunshine. In warmer weather, radicchio benefits from being planted in partial shade.
RESILIENCE
Adaptability to climate extremes. Radicchio is most susceptible to climate extremes when it’s young. As it matures, it becomes more resilient and can pretty easily withstand cold and frost. In extreme heat it needs lots of moisture to taste good and fully thrive. Radicchio is not a particularly drought-resistant perennial and requires frequent watering, mulching, and moisture in order to yield the best flavor. The more drought- or heat-stressed radicchio is, the more bitter it tastes.
Drought resistance. Radicchio is not a particularly drought-resistant perennial. It requires frequent watering, mulching, and moisture in order to get the best flavor. Dry, hot conditions can alter the flavor of your radicchio. The more stressed radicchio is, the more bitter it tastes.
PREP YOUR SOIL
Optimal soil type. Radicchio can be grown in a broad range of soils, from sand to clay. For the best-tasting radicchio, plant it in well-drained soil packed with nutrients.
PLANTING
When planting indoors. Start seeds in late spring, about three to four weeks before your last frost. Seeds are best sown when temperatures are cool. if you wait too long, radicchio seeds become dormant when soil temperatures rise above 60 degrees. Plant two seeds per two-inch pot, about one-quarter inch deep. Thin to the healthiest seedling once plants have sprouted three leaves. No need to worry about keeping these seedlings warm. Save room on your heat mat for the more delicate seedlings that need heat to grow strong.
When planting in the garden. Once seedlings are three inches tall, transplant them into the garden about eight inches apart. Don't worry about a late spring frost as these cold-loving plants can weather cold snaps. If you're skipping the indoor containers and planting directly in the garden, sow a few seeds per foot before the temperature climbs above 70 degrees. Keep newly planted areas moist until all the seeds have sprouted. After your plants grow to be about a five inches tall, thin them by snipping seedlings at the base of the plant so you're left with plants eight to 12 inches apart. Don't fret too much about the spacing; over the years plants will bunch together.
Growing
Radicchio grows much like a head of cabbage. Moisture is particularly important for radicchio flavor so it’s important to mulch to conserve water. Mulching your radicchio will also help curb weed growth. This vegetable’s shallow root system makes weeding hard to do without damaging the plant, so mulch is your best defense. During the summer heat, radicchio does best in afternoon shade. Too much heat stress will cause it to bolt, or flower early, which makes the leaves too bitter to eat.
Tip: To increase its sweetness, blanch its heart. This involves putting a bag or box over the radicchio heads a week before harvest so the leaves and stalks turn white. If you have a long-leafed variety you can tie the leaves together into a tight pod on top of the plant for the same effect.
WaterinG
Growing radicchio requires one to two inches of water per week. Once the head starts to form and about two weeks before harvest, increase the amount of water to up to three inches per week. This will reduce the risk of bitter heads.
Mulching
Keep your roots well-protected and moist by mulching your radicchio using crowns and leaves leftover from earlier radicchio plants. Any other type of mulch - leaves, straw, or wood chips - is fine, too.
CHALLENGES
Pests. As with cabbage and other lettuce-type plants, radicchio is prone to aphids, ants, and thrips. Aphids and thrips are easily brushed off plants but for large outbreaks, an insecticidal soap will keep populations from exploding. Ants can be eradicated by using peppermint oil as a barrier around your beds.
Diseases. Radicchio can develop various types of powdery mold if not well-drained. So make sure the soil isn't too wet. Once plants are infected it's very difficult to treat but it does help to remove any infected leaves.