Master Gardener: Growing lettuce in the hot, hot days of summer

There is nothing better than growing and eating your own garden salad greens. I love planting lettuce from seed in the spring and picking leaves for a daily bowl. It's typically the first thing that comes up in my spring/early summer garden. But, living in Placer and Nevada counties, most of us must pull any remaining lettuces by July. After all, lettuce is a cool-season vegetable. What about growing lettuce in the summer? Is it even possible? Maybe. Let's look first at planting lettuce from seed. Lettuce seeds germinate poorly in warm or hot summer soil. Heat causes seed dormancy. Lettuce typically "bolts" in high temperatures. The leaves turn bitter as they begin to flower. Leaves wilt and toughen if lettuce is water stressed in the heat. What do we mean by "bolting"? It simply means the plant sends up a flower stalk and goes to seed. This is common with cool-season greens like lettuce, arugula, spinach and some leafy herbs such as cilantro. So, what can you do? Ideally, for tasty lettuce growing, you need to keep your soil temperatures between 45 and 80 degrees. Keeping below 80 degrees is hard to do here. Fortunately, there's a trick to preparing a place to plant and even keeping it growing without bolting. Choose a shaded place and then moisten the ground. Cover it with a piece of cardboard for several days. You can drop the soil temperature considerably. (I tried this and the soil temperature is actually cool.) When you do plant from seeds, sow the seeds a quarter-inch deep and 6 inches apart in rows set 12 inches apart. Mist the soil daily with water so it remains moist. Lettuce seeds should germinate within one week at temperatures between 65 and 80 degrees Fahrenheit, and most lettuce will sprout eventually if the temperatures don't exceed 95 degrees. So, you will have to keep summer-planted lettuce in the shade. Plant them on the shady side of taller vegetables. I'm trying mine beneath tomatoes and peppers. Or use shade cloth. One other option is to use transplants from your local nursery. Later in the summer, grow loose-leaf varieties that are heat-resistant or slow-bolting rather than varieties that form heads. Look for "bolt-tolerant cultivars" such as Muir Organic Lettuce Seed. Several years ago, the Sacramento Master Gardener demo garden at the Fair Oaks Horticulture Center had success with Jericho, Red Cross, Nevada, Paradai, Merlot and Year Round Bronze Oak Leaf. Some bolted in as little as three weeks, with a few taking almost 10 weeks to bolt. Alternatively, use transplants from your local nursery or germinate seeds indoors in containers away from heat and then plant in the shade. In addition, use organic mulch to retain soil moisture. Try to keep your leaves off the ground. I used cardboard pieces to keep the leaves up. Inspect plants for insects and diseases. Hand-pick and destroy destructive insects. Remove diseased or dry leaves, and if they are too far gone, pull them. Don't skimp on water. Keep your lettuce growing fast to prevent wilting and bolting. Add soil nitrogen such as a liquid fish emulsion fertilizer to encourage growth. Make successive plantings if planting early in April and May. Or, bring in transplants to replace spent plants available even now, as at Eisley's. Cut your leaves often and keep coming back to harvest more. And if your experiment doesn't work, just plan to seed lettuce in your garden in late September for winter harvest.