Vegetable · Asteraceae
Radicchio
Cichorium intybus
As the cold deepens, radicchio turns a rich red laced with white, its leaves folding into a firm, tight head.
Full sun
Every 3–7 days
60–85 days
USDA 3–9
Overview
Radicchio shows up as a firm, rounded head of deep red leaves, close in size and shape to a small red cabbage. It sits in the Asteraceae family as a form of Cichorium intybus, a biennial grown as a fall crop. Each leaf runs deep red across the blade and pales to crisp white along the ribs, and the whole head packs down tight and heavy for its size. The flavor matches the look: sharp and bittersweet, sharper still after cold nights.
The color is a response to cold, not a constant. Grown into cool fall weather, the leaves darken from a dull, greenish red into a deep, saturated red, and the bitterness eases as they turn. Under summer heat the plant does the opposite: it stretches upward, throws a flower stalk, and the leaves stay coarse and green. In the cool, the same plant tightens into a dense, red-and-white head.
Up close the plant stays low and compact, standing only 6 to 12 inches (15 to 30 cm) tall. The outer leaves curve around a firm heart, each blade colored deep red with a broad white midrib running its length. Because the color holds through light frost, the red stays vivid on the plant well after softer greens have collapsed.
Care
The short version: full sun, even water of 1 to 2 inches a week, and rich, well-drained soil, timed so the head fills out deep red in the cool of fall.
Light
Radicchio wants full sun and takes only a little partial shade where late summer stays warm. Under strong light the plant grows thick and sturdy, and the leaves close into firm, deeply red heads.
Water
Keep the soil evenly moist, about 1 to 2 inches of water a week. When the plant goes dry or the watering turns uneven, the leaves grow harsher and more bitter and the head stays slack and open, so water more often in fast-draining sandy ground.
Soil
Set radicchio into fertile, well-drained soil thick with organic matter. A pH of 6.0 to 6.8, just acidic, is where the roots take hold best.
Temperature
Radicchio is built for the cold, holding across 19°F to 75°F (-7°C to 24°C). Young plants stand up to frost near 20°F (-7°C), and it is that autumn chill that pulls the red deep into the leaves and softens the bitter edge.
Humidity
Plain outdoor air suits the plant, so there is no humidity mark to hit. Airflow counts for more, since red leaves packed close and left damp are the ones that spot and rot.
Feeding
Work a complete fertilizer such as 10-10-10 into the bed before planting, then side-dress with nitrogen about 4 weeks after transplanting. Cut the nitrogen once the head begins to close, or the plant keeps pushing loose green leaves instead of a tight red heart.
Pruning
Radicchio needs no pruning. Peel away the outer leaves as they bruise or spot, and clear old debris so pests and disease do not settle around the plant.
Size & spacing
The plant keeps low and dense, only 6 to 12 inches (15 to 30 cm) tall and 8 to 12 inch (20 to 30 cm) across. Give each head that width so the leaves can fold in tight and air can pass between the plants.
When to plant
Radicchio colors up as a fall crop. Sow in summer and set the plants out in late summer, then watch the leaves close and redden as the weather cools, since cold is what turns the head deep red and firm.
Northern hemisphere
Southern hemisphere
Typical months for a temperate climate: start earlier in warm zones, later where spring frosts linger.
- Sow: Early to mid summer (start seeds indoors in July for transplanting in August for a late-season fall crop)
- Plant: Transplant in late summer (August) for fall harvest, or direct sow about 75-85 days before the anticipated maturity/harvest date
- Harvest: Fall (heads harvested as cool weather improves color and flavor)
Hardiness
USDA hardiness zones: 3–9
Temperature: down to -40°C
Troubleshooting
Most of what shows on a radicchio plant traces to heat at the wrong time. A tall stalk and open, coarse leaves point to summer warmth, while chewed and spotted foliage points to pests and disease. Match the look of the plant below and act early on the first signs.
Yellow, twisted leaves and stunted, deformed shoots
The yellowing and twisting are aster yellows, a phytoplasma that leafhoppers carry between plants, and no plant recovers once it is struck. Pull the affected plants and destroy them so it spreads no further. Holding leafhoppers and weedy hosts down is the only guard against it.
Fix:
- Remove and destroy infected plants
- Control leafhoppers
A tall stalk pushes up and the head never closes
That rising stalk is bolting, and summer heat is nearly always the cause. As the plant runs to seed the leaves turn coarse and bitter and the head opens out, so cut it before it goes further. The fix is timing: sow so the head fills out and reddens in cool fall air rather than midsummer heat.
Fix:
- Harvest promptly before quality declines further
- Replant timing so heads mature in cool fall weather
The leaves stay open and the head never firms
A loose head shows warmth held on while the leaves were trying to fold in, or soil that ran dry and lean. Keep the water even and the fertility up so the plant can wrap. Then set the crop to head in cool fall weather, when the leaves close tightest and color deepest.
Fix:
- Ensure consistent moisture and adequate fertility
- Adjust planting date so heading coincides with cool weather
Chewed leaves, small round holes, and seedlings cut at the base
Several pests mark the leaves: cutworms sever seedlings right at the soil, slugs leave shining slime and torn holes, and flea beetles punch the blades full of tiny round shotholes. Handpick or trap what you can, and treat aphids and caterpillars with insecticidal soap. Frequent scouting and a weed-free bed keep most of them off the plant.
Fix:
- Handpick or trap slugs and cutworms
- Use insecticidal soap or appropriate controls for aphids and caterpillars
Toxicity
For all its bitter bite, radicchio is only a salad vegetable, and the leaves are grown to be eaten. It carries no toxic risk to people, pets, or livestock. A pet that chews a red leaf comes to no harm.
Safe for
People · Cats · Dogs · Horses · Rabbits · Livestock · Birds
Cats None
Radicchio is safe around cats. A curious bite of a red leaf will not poison one, though these bitter greens hold little for a cat to want.
Dogs None
Dogs come to no harm near these leaves. A stolen scrap of the red salad green does nothing to them.
Horses Safe
Horses are safe with radicchio. Chicory is a familiar forage plant and carries no toxic risk for them.
Rabbits Safe
Rabbits can eat radicchio safely, and many take to the bitter red leaves. Offer it within a mix of greens rather than on its own.
Livestock Safe
Cattle, goats, and sheep graze chicory with no ill effect, and it is even sown on purpose as a pasture forage.
Birds Safe
Backyard hens and other birds can peck the red leaves freely. Nothing in radicchio does them harm.
People Safe
For people, radicchio is a salad vegetable eaten raw or grilled, red leaves and all. The bitterness is its character, not a warning.
No special handling precautions; an ordinary edible salad green.
Varieties
The radicchio types in most gardens differ mainly in the shape of the head, from the round red globes of the Verona forms to the long, tapering leaves of the Treviso forms. These are the ones to know.
Rossa di Treviso
An Italian heirloom whose head grows long and tapered, its leaves streaked deep red against white.
Rossa di Verona
The variety that rounds into the classic radicchio globe, deep red with bright white ribs cutting through it.
Giulio
A dependable round-headed selection that fills out well in a home garden.
Firebird
A reliable cultivar that closes into a firm head time after time.
How to propagate
Radicchio starts from seed, sown straight into the bed or raised under cover before the young plants are set out for fall.
SeedModerate
Start indoors in summer (e.g., July) for transplanting in late summer, or direct sow; seeds germinate best at 65-70°F and germination drops above 80°F. · Roughly 60 to 85 days from sowing to a mature head depending on cultivar and conditions.
Radicchio grows from small seed by two routes. Sown straight into the ground it sends down one strong taproot, while seed raised under glass in summer transplants cleanly into a fall crop. The seed sprouts best at 65°F to 70°F (18°C to 21°C) and falls off sharply above 80°F (27°C), and the plant needs 60 to 85 days from sowing before the head is full.
Myths
Radicchio is just a red-leaved lettuce.
The red leaves fool the eye, but that is all. Radicchio is a chicory in the Asteraceae family, not a lettuce, and the bitterness rides on that difference. It also takes a longer season of about 60 to 85 days, and its deep red color and full flavor only arrive once cool fall weather sets in.