Personally I have found that transplanting works well. You can thin the rest to eat and leave a few plants where you have sown to allow to grow. These are the first to be eaten at my house, because they are not under the hoop house. Because I was a little busy with a newborn my transplanting was delayed a bit, which turned out to be better because the hurricane came through! I transplanted my radicchio on September 10th this year. As you can see they are pretty sad looking for about a week, then they start to perk up. Just make sure you get as much root as you can when you dig them up!