By Matt Gibson
Related to both chicory and endive, radicchio is a perennial vegetable cultivated for its leafy greens (radicchio foliage is actually more commonly found in various shades of red, not green). Radicchio is also commonly referred to as Italian chicory, and is often found in Italian recipes as a flavoring agent and a vegetable.
Most Radicchio cultivars produce red leaves which are known for their bitter flavor. Radicchio typically forms rounded heads that grow to sizes that range from baseball-sized to grapefruit-sized, depending on the cultivar. Growing radicchio will bring a vibrant pop of color to your edible garden, and a strong, unique flavor to your kitchen. Read on to learn everything you need to know about how to start growing radicchio in your vegetable garden.
Varieties of Radicchio
In Italy, there are upwards of 15 different varieties of radicchio available to gardeners in different regions of the boot. The majority of these varieties are not commonly cultivated outside of Italy, and most are impossible to find in the United States. In the US, there are five radicchio varieties that you can find at nurseries and farmer’s market stands. We will give a bit more information about each of these five so that you can find the right one or ones for your garden.
The most common variety of radicchio in the United States is the Italian cultivar Radicchio Rosso di Chioggia, or Chiogga for short, which has dark red leaves and a round cabbage-like head. This cultivar is the radicchio you will most often find in the produce department of your local grocery store or on the tables at your local farmer’s market. Visually similar to purple cabbage, but packing a much stronger flavor, Chioggia radicchio heads are easy to find, and available year-round. The top Chioggia cultivars are Palla Rossa and Rossa di Verone.
The Radicchio Rosso di Treviso radicchio variety, also simply called Treviso, is known for its white ribs and more elongated, football-like head shape. Visually similar to a big, red endive, the Treviso radicchio has a mild but quite bitter flavor that can be mellowed-out through cooking. Traviso Tardivo radicchio is another variety available to US gardeners that requires a longer growth cycle than other varieties, which increases the depth of its flavor. A beautiful garden specimen, the Treviso Tardivo looks like a head of lettuce, but with a rose-like center. The extended growth period not only improves the taste, but also results in a firmer texture and a more complete structure, which allows the vegetable to keep its shape better and wilt less during cooking.
Castelfranco radicchio heads are another common variety in the United States. Instead of the typical red leaves that the vegetable is known for, the Castelfranco variety boasts creamy white foliage with red flecks. Castelfranco is a bitter green, but it also has a complex flavor with underlying notes that can be brought forward when cooked. Though more rare than the other four radicchio varieties listed here, the Puntarelle radicchio is a must try variety that should be blanched for the best possible flavor and served warm with butter like Brussels sprouts or asparagus. The odd-looking plant looks like a fennel clump sprouted asparagus stems from the top of the clump.
If you get particularly lucky and happen to come across one of the more unusual radicchio varieties such as Bassano, Chioggia Giant Catalogna, Fior di Maserà, or Lusia White, buy them immediately. If you happen to see seeds or seedlings for any of those varieties, you lucked out, as they are all unique and complex in flavor and quite rare to find outside of Italy.
Growing Conditions for Radicchio
Radicchio is a cool season crop that grows best in spring or autumn. Radicchio is a perennial plant, but it is often grown as an annual. However, if the head is gently and precisely cut from the roots in the fall, the roots have a good chance to live through the winter to produce another head.
Plant radicchio in full sun in a nutrient-rich, well-drained soil. Keep the substrate evenly and consistently moist. Provide one to one and a half inch of water per week and check regularly to be sure the soil never dries out completely, as it will turn the leaves too bitter. Provide plenty of water, and the leaves will turn sweet instead, as they are seasoned by the cool fall weather.
Radicchio can be grown in either the spring, summer, or fall depending on the region you live in. The common Chioggia variety, however, is best suited for cool weather climates. Though technically frost tolerant for short periods of time, any amount of exposure to high heat will burn radicchio’s foliage. It will survive in a very versatile temperature range, between 30 and 90 degrees Fahrenheit, but its leaves will suffer in high temps.
Radicchio plants love getting lots of sun but it can stand some shade as well, especially during very warm summers. Radicchio adapts well to a wide range of soils, from sand, to loam, or even clay, but it especially likes moisture, very good drainage, and a pH between 7.5 and 8.0.
How to Plant Radicchio
Start your radicchio seeds indoors between 12 and eight weeks prior to the last full frost. If you’re starting with seedlings, transplant them into your garden beds two weeks before last frost. For an autumn or winter harvest, plant your radicchio seeds in the late summer. Plant seeds one-fourth of an inch deep and two inches apart. Once seedlings start to mature, thin back to eight to ten inches between each sprout to insure proper circulation.
Radicchio plants will survive in temperatures between 30 and 90 degrees F, but prefer temps between 45 and 65 degrees F for most prolific growth. They prefer full sun but will grow well in light shade locations also. Radicchio seeds should sprout around five to seven days after sowing if soil temperatures are around 60 degrees, but might take as long as two weeks to sprout in colder soils.
Irrigate regularly, keeping the soil moist until seedlings mature. Amend the soil with plenty of compost prior to planting. Practice crop rotation, making sure not to plant radicchio where endive, radicchio, chicory, or escarole have been grown in the past few growing seasons. To extend your harvest, plant new seeds every few weeks for longer harvest periods. Provide half strength servings of an organic feed like fish emulsion to fertilize your radicchio during the growing season. Feed once in the spring once plants are established and once around mid-summer.
Care for Radicchio
Radicchio care is fairly simple. Pull up weeds around radicchio plants regularly or mulch to prevent weeds from taking root. Mulching is best, as radicchio plants have shallow roots, which can easily be disturbed unnecessarily while pulling up weeds.
Keep your radicchio watered well, irrigating manually during dry spells. Consistent moisture will lead to lots of growth. Supply at least one inch of water per week via rain or irrigation or a combination of both. Keep up waterings throughout the growing season. A rain gauge may be helpful in determining whether or not to add water near the end of each week. A drip irrigation system is preferred to help keep the leaves dry to avoid disease issues. If drip irrigation is not an option, water at the base of your radicchio plants and pat dry the leaves afterwards. Do not let the soil get over-saturated or water-logged for any period of time.
How to Propagate Radicchio
Radicchio can be propagated by seeds or transplants. Seeds stay active for five years. To learn more about growing radicchio from seed, consult the, “How to Plant Radicchio,” section above.
Garden Pests and Diseases of Radicchio
Alternaria Leaf Spot: Alternaria manifests as small rusty brown lesions with white or gray middles that appear on the top side of leaves. The lesions can go all the way around the stem of the plant, causing the affected branch to wilt. Alternaria is at its worst when the weather is warmer, wetter, or more humid than usual.
Prevent alternaria leaf spot by watering plants from the base instead of using a sprinkler system or allowing the foliage to be splashed by watering from above. Avoid overwatering your plants, and do not work around them when foliage is wet from rainfall, morning dew, or irrigation, as wet conditions encourage the spread of alternaria leaf spot. Spacing out your plants at the appropriate distance and keeping them pruned, as well as any other measures that facilitate air circulation, can also help stave off alternaria leaf spot.
If you see alternaria leaf spot on a plant in your garden, use clean, sterilized shears to snip away the affection portion of the plant as quickly as possible to avoid allowing the disease to spread. Do not use diseased plant material in your compost. For more information, you can read our article Dealing With Alternaria Blight.
Aphids: Aphids are tiny insects that tend to appear in groups on the undersides of plant leaves when the plant is infested. Aphids can be many colors, including black, green, red, or peach, but all aphids are very small and can be differentiated from other insects by the way their damage looks and their common hiding spot on leaf undersides.
Because aphids suck the juice from inside plant cells, symptoms of their feeding include distorted, misshapen, curled, twisted, or withered foliage. The insects and damaged foliage may be accompanied by a sticky clear substance called “honeydew” that will attract ants.
Natural predatory bugs such as lady beetles or braconid wasps can be introduced to the garden to keep aphid populations down. You can also blast them off with repeated rounds of water from a high-pressure water hose nozzle or fight them with insecticidal soap. For more information, you can read our article All About Aphids, And How to Kill Them. You may also be interested in our article How to Spot and Get Rid of Aphids with Organic Methods.
Bacterial Leaf Spot: Bacterial leaf spot infection results in water-soaked lesions that appear on the foliage of affected plants. The leaf spots start off a brown color, but their presence eventually causes the leaves to change color to yellow. Bacterial leaf spot is more likely when the weather is cool. If you see signs of bacterial leaf spot in your garden, remove the affected plants and dispose of them immediately to prevent spread of the disease. Do not include diseased plants in your compost heap.
Use crop rotation with plants that are from a different family and not susceptible to bacterial leaf spot to help keep the disease at a minimum in your garden. Do not work in the garden around plants that are vulnerable to bacterial leaf spot when the plants or the ground are wet from rain, morning dew, or irrigation, as wet conditions contribute to spread of the disease. For more information, you can read the University of Maryland Extension profile on bacterial leaf spot.
Black Rot: Not to be confused with black root rot (normally referred to simply as “root rot”), black rot is a bacterial plant disease that is at its worst when the weather is especially warm or humid. The leaves of infected plants break out into V-shaped lesions in shades of yellow and orange that appear on the edges of the leaves. Where the lesions appear, the foliage withers until it dries completely and falls from the plant.
Prevent black rot from becoming a problem in your garden by rotating crops with a different type of plants entirely that are not susceptible to black rot. Water plants no more than is needed, and aim the moisture at the base instead of using overhead irrigation or watering from above and letting the moisture splash the plant leaves. Do not work around plants susceptible to black rot when it is wet in the garden due to rain, dew, or irrigation, as moisture allows black rot to spread.
Any measure that increases air circulation around your plants, such as spacing them out sufficiently or pruning them well, will help keep black rot at bay. Black rot can find a home for the winter in invasive weeds, so make sure to keep your garden and the area around the edges of your garden clear of weed plants. For more information, you can read The University of Wisconsin-Madison Horticulture Division of Extension’s profile on black rot of crucifers.
Cabbage Looper: Cabbage loopers are green caterpillars with white stripes along their sides that measure an inch to an inch and a half long. You can tell them apart from other green caterpillars by the looping, inchworm-like gait for which they are named. After the cabbage loopers have matured and transformed, you may see white moths flitting around the brassicas in your garden. These moths can lay eggs on your plants that will hatch to create more cabbage loopers. Cabbage loopers will feed on radicchio and any plant that is a relative of the cabbage and can leave holes, missing sections of foliage, or tunnels in their wake.
You can protect your plants from ever having cabbage looper eggs laid on them by setting up floating row covers as soon as your radicchio and any other vulnerable plants are introduced to the garden. If you see one of the green caterpillars in your garden, pick it off the plant and drown it in a bowl of soapy water. Parasitic wasps can also be deployed to keep cabbage looper populations down. Botanical Bt (Bacillus thuringiensis) is a natural insecticide that will work against cabbage loopers without dealing too much damage to your friendly neighborhood pollinators and other beneficial insects. For more information, you can read our article How to Control Cabbage Looper.
Damping Off: Damping off is a fungal disease that tends to strike when plants are at the seed or seedling stage, and it can spell disaster for entire crops of many plant types. Seeds may fail to sprout or young plants may wilt and collapse for no apparent reason. The disease happens most when conditions are wet and the temperature is above 68 degrees Fahrenheit (20 degrees Celsius). It can also be a problem when the soil is too heavy in nitrogen, often due to too much nitrogen-based fertilizer.
Consider keeping your baby plants hydrated by misting them with a spray bottle to avoid excess moisture and overwatering. Use fertilizers as directed to avoid ending up with too much nitrogen, which can encourage damping off. Don’t let seedlings crowd one another too much, and don’t be afraid to thin them out so the strongest have a better shot at survival. In addition to thinning out seedlings, any strategy that improves air circulation will help prevent damping off (such as finding a spot that is not sheltered against breezes or removing objects that block the wind). If you use containers more than once, sterilize them before reuse by scrubbing them in soapy water and then rinsing them in a solution of one part bleach to nine parts water.For more information, you can read our article How to Prevent Damping Off.
Downy Mildew: Downy mildew is a fungal disease that is easy to recognize because of the fuzzy white or gray patches it creates on the undersides of plant leaves. After a while, the disease will move to occupy the top side of foliage as well.
Keep downy mildew at bay by rotating crops with a different family of plants that is not susceptible to this disease. Do not use overhead irrigation or water plants from above. Instead, aim water at the base of your plants so their foliage is not splashed with moisture. Ensure good air circulation by spacing plants out appropriately and pruning them as needed. Do not work around plants vulnerable to downy mildew when conditions are wet (after rain, irrigation, or when morning dew stands on the plants), as moisture helps downy mildew to spread. For more information, you can read our article Identify, Prevent, and Treat Garden Problems: Downy Mildew .
Flea Beetles: Flea beetles are tiny jumping insects that will consume your plant leaves and spread disease at the same time. To keep their population at a minimum, rotate susceptible crops out with plants from another family entirely that don’t tend to struggle with flea beetles. You can also install floating row covers when plants are young to prevent flea beetles from damaging them when they would be hit the hardest. For more information, you can read our article How to Fight Flea Beetles.
Leafminers: Leafminers chew tunnels in the surface of your plants’ leaves as they eat, and you may even be able to see the tiny dark dot of the insect’s body at the end of the winding path leafminers leave behind. The larval maggot form is yellow and cylinder-shaped, while adult leafminers are tiny fly-like bugs in shades of black and yellow.
While leafminers do lots of ugly damage to foliage, they are not normally fatal to the plant. If you see signs of leafminers on one of your plants, remove and dispose of it as quickly as possible to curtail spread of the infestation. Do not include plants infested with leafminers in your compost. For more information, you can read our article How to Fight Leafminer Insects.
Slugs and Snails: Most gardeners have seen what slugs and snails can do in their gardens more than they would like. They tend to chew large jagged areas out of plant leaves, and if plants are especially young, they may mow them down entirely. You can tell that slugs or snails have been at work when the damage is done overnight and accompanied by a silvery trail. Slugs and snails are more of a problem when the weather is wet.
A ring of diatomaceous earth around your vulnerable plants will keep slugs and snails away, as the DE is painful for them to cross with their soft bodies. Some gardeners report they were successful using coffee grounds in the same way one would use DE against slugs and snails. There are many different kinds of traps you can make with household items to catch slugs or snails if they continue to be a problem.
For more information, you can read our article How to Protect Seedlings from Slugs and Snails, which has tips to defend plants of all ages as well as instructions for making an electrified barrier against slugs and snails using copper tape. You may also be interested in the articles Gardening Quick Tip: Use Rhubarb Leaves as Slug Traps, Slug and Snail Pest Control, and How to Control Slugs and Snails in the Garden.
How to Harvest and Store Radicchio
Individual leaves can be taken at any time, or you can harvest the entire heads when they become firm to the touch, which usually takes approximately 60 to 65 days after the initial planting. Use radicchio like lettuce in salads or wraps. Cook radicchio by sautéing or steaming.
Harvest heads when they are young at any size you prefer. Young heads can be kiwi, baseball or even grapefruit-sized. The older the heads, the more bitter the flavor will be and the tougher the texture. The younger heads will be sweeter, tender, and less bitter. Bitterness can be tamed to a degree by cooking. Radicchio grown in the fall will hold together better and store longer than spring-grown radicchio.
Store heads in the fridge for three to four weeks in an unsealed and perforated plastic bag. Just after a frost, harvest snow-covered heads and remove frozen outer leaves, storing the remainder in a perforated unsealed plastic bag in the refrigerator. Frosted heads will also keep for around three to four weeks.
Radicchio is a common ingredient in Italian cuisine, where it is often cooked and paired with other vegetables to create tasty side dishes. Cooked radicchio is especially amazing when paired with eggs or cooked into omelets. Find new and interesting ways to use radicchio in your meals and enjoy this immensely flavorful and complex Italian vegetable grown fresh in your edible garden.