Radicchio

Most people who grow radicchio once never grow it again, and the reason is timing. A spring-sown radicchio head harvested in June is inedibly bitter — the plant tastes like it's trying to warn you away. The same variety, sown in midsummer and harvested after the first hard frost in November, can be sweet enough to eat raw. The difference is cold. Radicchio is a fall crop pretending to be available year-round in grocery stores.

The traditional sowing window is about sixteen weeks before your first fall frost — mid-July in many northern climates, late July or early August further south. The plant needs time to size up before cold weather arrives, but not so much time that it matures in the heat of August. A head that forms in ninety-degree weather tends to be loose, pale, and astringent. A head that forms as the nights drop into the forties tends to be tight, dark, and complex.

The real culinary product of a radicchio planting is often not the first head at all, but the second growth that comes after you cut the plant back. In late autumn, after the first frost has sweetened the outer leaves, cut the entire head off about an inch above the crown. Cover the stumps with a thick layer of straw or leaves — six inches or more — and wait. In two to four weeks, depending on how cold it gets, pale, tender secondary heads will form under the mulch. These are the blanched radicchio hearts that Italian growers have been producing for centuries, and they are markedly less bitter than anything that grows above ground in full light.

Radicchio can handle frosts down into the mid-twenties without serious damage, and the flavor improves noticeably after each cold night. The outer leaves may look ragged, but the inner head stays tight and protected. If a hard freeze is coming — anything below twenty degrees — pile more straw over the plants or throw a row cover on top of the mulch. The goal is to slow the freeze, not prevent it entirely.

What tends to go wrong is bolting in the heat. If a radicchio plant experiences a long spell of temperatures above eighty-five degrees while it's still young, it may send up a flower stalk instead of forming a head. Once that happens, the plant is done — the leaves turn woody and the bitterness intensifies. The fix is to sow later, so the plant is still small during the hottest weeks and sizes up as the weather cools.

Harvest the outer leaves as the plant grows if you want salad greens with bite, or wait for the full head to form and cut it at the base. The flavor is always better after a frost or two, and if you're patient enough to try the cut-and-resprout method, you may find that the second heads are the ones you remember.