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garden q&A: warm spring stifles radicchio

| Saturday, Sept. 8, 2012, 5:05 p.m.

Q: I have grown the same variety of radicchio for many years with no problems. For the first time last year and again this year, it would not form heads. Would you have any idea what went wrong?

A: Radicchio, sometimes called Italian chicory, is a “green” that has deep red leaves with white leaf veins. Much like Iceberg lettuce or cabbage, radicchio forms a tight cluster of leaves called a head. It is most often used fresh in salads where it has a slightly bitter flavor, but cooked radicchio is a personal favorite. The cooking process softens and sweetens the flavor.

Radicchio, like many other greens, prefers cool weather and often will not form a tight head if hot weather arrives too soon. Seeds can be sown directly into the garden in spring about four to six weeks before our last expected frost (I usually sow mine around early April).

Spring-planted crops are harvested sometime in early July. It's possible to grow a fall crop by sowing more seeds about eight to 10 weeks before the first expected autumn frost. Fall-planted radicchio may be less likely to go to flower as the plants are still very small when the temperatures are hot. The heads may be smaller than those from spring-planted radicchio but, with a blanket of floating row cover, they'll make a delicious addition to Thanksgiving, and even Christmas, dinner.

Late planting or warmer-than-usual spring weather are probably to blame for your radicchio not “heading up,” but you should be sure to avoid excessive nitrogen fertilization which also prevent the formation of tight heads.

Another item to note: Many heirloom varieties of radicchio can take up to 100 days to reach maturity while some of the newer hybrids mature a few weeks faster. The past few years have brought periods of very warm spring weather, so having a radicchio variety that matures a little bit faster could mean the difference between a tightly formed head and a plant that goes to flower before you can harvest a single leaf.

“Early Trevsio,” an Italian heirloom; “Guilio,” a bolt resistant, fast maturing cultivar; and “Firebird,” an early maturing hybrid, are good varieties for Pennsylvania gardeners.

Horticulturist Jessica Walliser co-hosts “The Organic Gardeners” at 7 a.m. Sundays on KDKA Radio. She is the author of several gardening books, including “Grow Organic” and “Good Bug, Bad Bug.” Her website is

Send your gardening or landscaping questions to or The Good Earth, 503 Martindale St., 3rd Floor, D.L. Clark Building, Pittsburgh, PA 15212.

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