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In hot weather, lettuce needs special care

Homegrown lettuce is so tasty and tender for salads. It's also cold-hardy, so it can be enjoyed almost year-round. But special tricks are needed to pick lettuce from the garden now, when it's hot.

This time of year, lettuce tends to bolt — that is, to flower and make seeds. Once a flower stalk starts pushing up through the whorl of leaves, those leaves turn bitter and tough.

Actually, flavor plummets even before the stalk becomes evident. Keep a close eye on your lettuces, and you'll see that the leaves undergo a slight color change from shiny, vibrant green to dull, slightly bluish green.

Like any plant or animal, lettuce has to reach a certain age before it can make seeds and reproduce. So one obvious way to keep your salad bowl filled with tasty lettuce is to keep sowing seeds so you always have young plants to eat.

I plant lettuce about every three weeks all summer. Just a little at a time, though, because three weeks after you start eating one planting, you'll be eating the next sowing's harvest.

Lettuce also bolts in response to the combination of long days, dry soil and hot temperatures. Spring and fall lettuce rarely bolt because, although the plants might be old enough to go to seed, the days are just too short.

You cannot do anything about summer's long days, but you can do something about water and heat. Start by always planting lettuce in soil well-enriched with compost, leaves, straw, manure or some other organic material. They all help soil to hold moisture.

Also water regularly, which makes lettuce taste better. Lettuce needs the equivalent of 1 inch of water a week, measured into a rain gauge or some other straight-sided container. If Mother Nature doesn't provide water, you do it: once a week with a sprinkler, which takes about an hour; or spread through the week with a drip-irrigation system.

You can also do something about the temperature. Just as you cool off by moving out of the sun, so can lettuce. The plants tolerate shade this time of year, so cobble together a temporary wooden or plastic frame for supporting cheesecloth, wooden lathe or some other material that offers about 25 percent shade. Or let your garden space do double duty, and grow lettuce in the dappled shade of cucumbers, squashes, gourds, tomatoes or pole beans trained up stakes or an inclined trellis.

Or plant lettuce near the cooler, eastern side of your house or garage. Frilly and red-leafed Lolla Rosa is a lettuce variety pretty enough to decorate a flower or shrub bed; the dappled shade beneath the other plants will keep Lolla Rosa from bolting, for a while at least.

And speaking of varieties, genetics also plays a role in how fast plants bolt, so plant those that are slower to do so. Among the best for growing in sultry summer weather are Blackseeded Simpson, Buttercrunch, Kagran Summer, Salad Bowl, Red Salad Bowl, Oakleaf, Deertongue, Diamond Gem and Graquerelle du Midi.

Merveille de Quatre Saisons lettuce is planted in the shade of tomato plants to help it deal with the heat of summer. (AP Photo/Lee Reich) - AP