I've been growing rosso trevisano variety all summer now. They are beautiful glorious plants and quite tasty (bitter but good) So far All i've been able to do with them is cook and eat them as if they were bitter kale. But I really want to get them to form heads! I've searched the internet far and wide and have been completely stumped in my search to find out the technique used to get them to make heads. The closest I got was one Italian newschannel youtube video that I couldn't understand. It seemed like they were digging them out in late fall and placing them somewhere dark. Is that true? I'm really really into this and am up for a project. If there is a way to do this that any of you can advise I'll do it!
I have sown a bunch of different chicory types around my garden, trying to get them to naturalize, and the Palla Rossa radicchio is the most problematic. I mostly get rosettes, but when temperatures are cool and the weather rainy, they start to form heads. None as nice as the ones on sale at Publix for $6 a pound, but mine stack up just as well flavor-wise. It seems to me that the best head formation is in January and February, when we have a good number of nights that go below freezing.
I love John's comment "control the weather"!
But in a way he's right.
The first year I planted radicchio it cam up sorta loose leaf style. It was a mix of seeds and I had never planted it before so I didn't know what to expect. I let it and some other lettuces go to seed to see how far and how true they would grow.
The following spring, right where all of that had been planted the previous summer, I had "beautiful" heads of radicchio pop up and grow. Very early spring, and only in the area that got morning sun and was shaded from about noon/1PM on. Turns out they were perennial, they grew for 2 years until I redid those bed to put in Hugel terraces.
Start looking next spring to see if they come up again in the same area and if you get heads instead of leaf. Oh, and they'll probably be sweeter as well, mine were.