May 7, direct seeded, is about right. You will get the biggest possible heads, though in a regular year they will be loose, not tight. This year, mild as it was, it would have been a good year to keep them under cover until February and see if they would for a tight head. Alas, I ate all my radicchio in Nov. Dec.

Keep in mind this is a winter vegetable for Zone 8 or 9. I don't grow good favas either, same reason. But loose head radicchios are just as good in salads as tight heads, IMHO, even better. You could also try self-heading radicchio, though I found it to be inferior.

I've grown several varieties of radicchio on purpose, and the ones with elongated heads never got as tight and crisp as those with more rounded heads. From an early sowing indoors, you can also get little secondary heads after the primary one is cut. These are often quite nice, a treat in summer when it's in-between season for many greens.

These days I mostly sow mesclun mixes that include the chicories (radiccho, endive and escarole), and gradually harvest lettuces, arugula, etc. until only the chicories remain. This gives me about all I need for fresh eating in June. I plant again in August, again pulling the baby lettuce and arugula, and in winter I place cloches or row covers over the dormant radicchio to keep the deer from pulling it out of the ground. These little cuties have broken dormancy and are gaining size day by day. They are now 4 inches across, so in a couple of weeks I will cut the primary heads high, leaving the root and a stub. It will produce a cluster of sprouts within two weeks, which I'll thin back to 3 or 4 sprouts. The thinning helps the secondary heads get big enough to have nice little hearts.

This is the way radicchio seems to want to grow in my garden, anyway.

Good radicchio is harvested in cool weather. In my garden, that means calculating harvest dates in late September at the earliest, and probably late October as optimal. I have harvested as late as December, with richly colored, tight heads after you peel away the frost-damaged outer leaves. Radicchio varieties have maturity dates anywhere from 60 to 100 days. Planting in spring will result in a harvest during the heat of summer, resulting in poorly formed and colored heads. I start a small percentage of the crop in June, but generally July and August plantings yield superior quality. The reason the groundhog ate your plants in September was because that's when they were becoming delicious.

Thanks! Bil 1 me, that gave me a chuckle, you're right, that is why that stupid groundhog ate my radicchio :) I think I'll try something different this year, and start a crop in August. I certainly haven't been successful with crops started in the spring. I'll enjoy some other greens through the spring and summer. And, FYI, my fence has been shored up with some strong hardware cloth, dug a foot into the ground this year. Hopefully, that stupid groundhog and his offspring find somewhere else to eat.

Hi Michele
I also garden in Massachusetts, in Beverly. I love radicchio and grow a lot of it, as many different varieties as I have been able to find. There are varieties carried by Johnny's that head well even in the summer - Chioggia Red Preco No.1, Indigo (F1), Fiero (Fi). I'll start seeds indoors this week and plant out seedlings early April under row covers. Last year I was surprised to find seedlings for sale near me that I couldn't resist buying. They did well for me. One spot was Goose Cove Gardens on Gee Street in Gloucester. I really like to support them. They're a family run operation and strictly organic. They won't sell plants until it's the right time for planting and they select varieties that do well around here. The other spot is Green Meadows Farm in Hamilton. They are an organic farm that runs a CSA, of which I've been a member for several years. Last fall I gave the greenhouse manager packets of all the radicchio varieties carried by Franchi Seeds. I'm hoping she'll start them and also have seedlings to sell this year.
Lou

I have tried April plantings, but radicchio really stalls and will not grow well until it is warm. Hence the May recommendation.

Hi Lou, thanks for the recommendations on radicchio and nurseries! We are neighbors, I'm in Salem :) Happy Gardening!