Answer: Radicchio is one of those plants that should be harvested continually by pulling off the outer leaves and allowing the center of the plant to continue growing. It sounds as though you're waiting until the entire plant is completely mature before harvesting. The outer, older leaves can get quite tough and bitter by the time the center of the plant stops growing. Try pulling or cutting the outer leaves off the plant while they're still tender. Otherwise, just expect to discard the outer leaves when you harvest the entire head.
General growing guidelines is as for lettuce; Sow seeds in rich, moist soil and water regularly. Radicchio grows best in the cooler months of spring and autumn.
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