Lettuce (Lactuva sativa) is generally a cool-season crop, but choose your varieties carefully, give some extra thought to where you plant, and your salad days could last all summer.
Read seed packets to make sure your choice is suited for warm weather.
Some varieties are more heat-tolerant. Look for those. Dark red Ruby, frilly Red Sails or crisp chartreuse Nevada are warm-weather favorites. Cos varieties, which many of us know as Romaines, are also slower to bolt (go to seed and turn bitter) than varieties like iceberg, which are normally successful only in really cool weather.
Lettuce thrives in cool weather, and lettuce seed will not germinate when the soil is over 80 degrees Fahrenheit, so when the weather is hot, start your seeds between moist paper towels in a plastic bag. In two to three days, you can plant them out in warm soil with a much higher germination rate.
There are methods to extend your harvest, too. First, find the cooler areas of your garden to site your new lettuce beds.
“Cut and come again” is a good way to keep in the greens, sowing a band or bed of seed every two weeks. Keep the seedbed watered well during germination. Lettuce is shallow-rooted. Frequent and light watering after germination produces the most abundant and leafy crops.
When greens, which can be one variety or a custom mix, are tall enough to cut for salad, begin your harvest. You can cut the same bed several times before it is depleted. Scissors make the job easier.
Another method that keeps head lettuce from bolting is the practice of digging up the lettuce plants and transplanting them, often back into the same place. The shock to the system slows the development of the lettuce, setting back the urge to set seed and giving your lettuce a longer garden life.
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At a Master Gardener conference years ago, a hydroponic lettuce grower explained he had discovered it was the temperature of the root zone that caused his lettuce to bolt. By keeping the root zone cool, his lettuce did not get the signal to turn bitter and go to seed.
In my garden, I have found other ways to keep root zones cooler and the lettuce growing longer. Interplanting in the shade of tall beans, corn, tomatoes and peas can give your lettuce a cooler, shadier place. Parts of the garden that are not suitable for your summer tomatoes, squash or melons because of too much shade or moisture, can sometimes be a perfect spot for lettuce, summer spinach or other greens. Mulching can also keep root zones cooler and conserve water for lettuce and many of your other crops.
Lettuce comes in many shapes and colors. Consider planting beautifully textured hanging baskets designed with lettuce varieties on decks or balconies. Plant the baskets or pots the way you would any other decorative plant, at 4- or 5-inch spacing. Lettuces fill in beautifully and can be selectively and sustainably harvested for several weeks if you keep them watered and judiciously picked. There is something satisfying in picking out the perfect crunchy few leaves to adorn your summer tomato sandwich or the reddest, frilliest leaves from your full hanging basket to set off your cheese plate.
Lettuce comes in a variety of textures from buttery to crisp, flavors from mild to bitter and colors from purple to chartreuse. Lettuces look tidy in rows, fabulous in landscapes and after the salad days are gone, the flowers and seeds are a delight to the birds and the bees. It is a wonderful crop to experiment with since even square foot gardening in a patchwork of lettuces can give you a crop that is visually exciting, provides variety to all kinds of dishes and is easy to pull up and start all over.
If your lettuce is still bitter, wash it well, and after spinning the excess water out, wrap lightly in paper towels, place in plastic bags and store in the refrigerator. Often the bitterness will diminish after a day or two. Avoid storing lettuce near apples or pears, since the ethylene these emit cause the lettuce to decay and develop brown spots more quickly than normal.
Lettuce may be a cool-season crop, but there are a lot of reasons to try to grow it right through the dog days of summer. Good luck!
Napa County Master Gardeners answer gardening questions Monday, Wednesday and Friday, 9 a.m. to noon, at the UC extension office, 1710 Soscol Ave., Suite 4, Napa, 253-4221.