Lettuce That Can Stand the Heat

Gardeners love to compare notes, but it's always a little weird with my old friend Joyce Wilkie. She and her husband, Michael Plane, grow vegetables in Gundaroo, Australia, near Canberra, so our conversations have an upside-down quality to them. In February, when I'm deep in winter, Gundaroo is beastly hot. Right now, with my garden in the kickoff stage, Joyce is getting her winter greenhouses into fighting trim. This week I decided to pick her brain about lettuce. "Do any survive your summers?" I wondered.

Of course, it's not really about survival. A lettuce plant thinks it's doing fine when the combination of long daylight hours, dry weather and temperatures above 80 degrees causes it to bolt. This simply means it's time to make seed. The center of the leafy rosette begins liftoff, rising several feet in height if you let it, and eventually making flowers. The ancient Egyptians, who cultivated lettuce, found this a powerful image, equating the plant's upward thrust and milky sap with virility. Modern kitchen gardeners are less impressed. Once a lettuce "starts to move," as Joyce puts it, it acquires a bitter taste that generally spoils it for salads, although in many countries (France and China come to mind) it is commonly braised, stuffed and baked, or simmered in soups.

"We never grow the frilly, fancy ones in summer," Joyce says. "We grow mesclun instead, sowing it in the shade and cutting and re-cutting while it is small. For heads I grow the big, hard, crisp types, which are so crunchy and sweet my boys pick them and eat them like apples. The cos [romaine] types aren't bad, either. But you can never allow lettuce to get stressed. Transplant stress, wind stress, water stress -- avoid all these and Bob's your uncle." The Wilkie-Plane solution involves a shade cloth, stretched across a framework made from rebar and black poly pipe. The reduction in light, coupled with vigilant watering, holds that procreative urge at bay. (For more about Michael and Joyce's methods, go to http://www.allsun.com.au/ .) This was excellent, clear advice for any hemisphere, except for the phrase "Bob's your uncle," which turns out to be an expression meaning, roughly, "It's as simple as that."

I, too, have practiced the mesclun trick, snipping a mix of lettuces too young to even think about bolting. The Cook's Garden Web site has a "Lettuce Heatwave Blend" you might try. And I've noticed that crisphead lettuces are making a comeback after years of ill repute. I'd skip the true iceberg type, pale in color and poor in nutrients, and grow the Summer Crisp, or French Batavian, varieties, such as the excellent Nevada. Ann Yonkers, who directs the farmers market at Dupont Circle, says the Batavians are favored by local growers once things start to heat up. I always keep an eye out for lettuce varieties developed in hot places, such as the Israeli variety Jericho -- quite heat-resistant for a romaine (Seeds of Change and John Scheepers Kitchen Garden Seeds both offer it) -- or the small, firm, crisp Anuenue (pronounced Ah-noo-ee-noo-ee), developed by the University of Hawaii and available from Johnny's Selected Seeds. Of the leafier types, you might succeed with Red Sails, Royal Oak Leaf, Black-Seeded Simpson or the French variety Kinemontpas -- a variation on a French phrase loosely translated as "boltproof."

In California it is quite common to grow summer lettuce in a shady spot. And shade cloth is easy to put over a lettuce row. Use the same wire wickets that hold up floating row covers in spring, when it's protection from the cold that you need. Joyce uses quite a dense weave -- one that excludes 70 percent of ultraviolet rays. I'd roll it up at the sides to permit good air circulation. Where summers are more humid than Joyce's, lettuce is prone to summer rots. A wide spacing will give it more air. Growing lettuce in the shade of tall crops such as pole beans, tomatoes or corn is another trick. Use a soil rich in organic matter to hold soil moisture better, and an organic mulch such as pine needles or leaf mold. This reduces the need for cultivation, thus sparing the plants' shallow roots.

Make small sowings every few weeks, so there is always a fresh young row coming along. By the time mid-August arrives, it's time to start lettuce for fall. Germination is tricky in hot weather. It's best to start seeds indoors in a cool spot such as a cellar, or cover an outdoor row with moistened burlap or a wooden board, checking daily for germination and removing the cover promptly once it occurs. If you keep the crop irrigated it should hang in there until the days are 70 to 75 degrees, with cooler nights and more rain -- just the weather lettuce likes best. And then -- Bob's your uncle!

The Cook's Garden, 800-457-9703,http://www.cooksgarden.com; Seeds of Change, 888-762-7333,http://www.seedsofchange.com; Scheepers, 860-567-6086,http://www.kitchengardenseeds.com; Johnny's, 877-564-6697,http://www.johnnyseeds.com.