Plant care
'Castelfranco' Radicchiotemperature & humidity
Cichorium intybus var. foliosum 'Castelfranco'
More about 'castelfranco' radicchio
Ideal temperature for 'castelfranco' radicchio
Temperature kills fewer 'castelfranco' radicchio plants than you'd think. What kills them is the micro-climate within a normal-temperature room — a leaf pressed against single-glazed winter glass, the hot dry updraft directly above a radiator, the cold blast from an AC vent. The thermostat reading at 10-21°C (50-70°F) is fine; the spot you put the plant in matters more. Below roughly 10°C growth pauses; cold beyond that pushes it into dormancy rather than killing it outright.
Cold tolerance & winter care
'Castelfranco' Radicchio is comparatively hardy (USDA Cool-season annual/biennial; zones 4-9 (frost improves flavour and colour), RHS H3 (hardy in milder winters; light frost sweetens the heads)). Within that range it tolerates a cold dormant spell outdoors; outside it, grow it in a container you can move under cover or overwinter in a cool but frost-free spot. Hardiness assumes an established plant in well-drained soil — a wet, cold root zone kills far more plants than cold air alone.
Humidity for 'castelfranco' radicchio
'Castelfranco' Radicchio sits happiest at around Ambient outdoor relative humidity. A field salad crop unconcerned with air humidity. Adequate spacing and airflow are what matter, helping prevent the bottom rot and fungal leaf spots that strike crowded, damp plantings. The usual low-humidity tell is crisp brown leaf tips and edges while the soil moisture is fine — a sign the air, not the watering, is the problem. If you need to raise it, the reliable methods are grouping plants together, standing the pot on a tray of damp pebbles (the pot above the waterline, never in it), or running a small humidifier in winter when indoor heating dries the air most. Misting is the least effective — it raises humidity for minutes, not hours.
'Castelfranco' Radicchio temperature & humidity — frequently asked questions
What temperature is best for 'castelfranco' radicchio?
'Castelfranco' Radicchio grows best between 10-21°C (50-70°F). Keep it out of cold draughts, off freezing windowsills in winter, and away from the hot dry air directly above radiators — the extremes matter far more than the average room temperature.
How cold can 'castelfranco' radicchio tolerate?
'Castelfranco' Radicchio starts to suffer below roughly 10°C. It tolerates a cold dormant period within USDA Cool-season annual/biennial; zones 4-9 (frost improves flavour and colour), but a wet cold root zone is more dangerous than cold air.
What humidity does 'castelfranco' radicchio need?
'Castelfranco' Radicchio prefers about Ambient outdoor relative humidity. A field salad crop unconcerned with air humidity. Adequate spacing and airflow are what matter, helping prevent the bottom rot and fungal leaf spots that strike crowded, damp plantings.
How do I raise humidity for 'castelfranco' radicchio?
Group it with other plants, stand the pot on a tray of damp pebbles (kept above the waterline), or run a small humidifier in winter. Misting only helps for a few minutes, so it is the weakest option for a plant that genuinely needs more humidity.
Can 'castelfranco' radicchio live outside?
'Castelfranco' Radicchio is rated for USDA zone Cool-season annual/biennial; zones 4-9 (frost improves flavour and colour) and RHS hardiness H3 (hardy in milder winters; light frost sweetens the heads). Within that range it can stay outdoors; outside it, grow it in a moveable container and protect the roots from a wet, cold winter.
More 'castelfranco' radicchio care
In the UK? Keeping 'castelfranco' radicchio warm in a UK home covers the radiator, single-glazing and heating-season humidity angle. Temperature and humidity are one piece. See the full 'castelfranco' radicchio care guide, its cold-hardiness guide, and watering schedule — humidity and watering problems are easy to confuse.