Ah, seasonal eating from the garden: asparagus and peas in the spring, vine-ripe tomatoes and sweet corn in the summer, squash in the fall and kale in the winter. One fly in the ointment (so to speak) is that summer is the season of salads, which gets you out of cooking in a hot kitchen. Only problem is, growing summer lettuce is a challenge. Not being one to give up gracefully (I LIKE summer salads, especially with fresh ripe tomatoes!), I get sneaky when it comes to summer lettuce.
The variety really does make a difference. Leaf lettuce of any kind is generally a better choice than head lettuce or romaine for really hot weather. Of these, butterhead and oakleaf varieties tend to be top of the list for heat resistance. The more colorful lettuces, especially the dark reds and magentas, don’t hold up as well to heat. Lettuces that are speckled do OK, though. In my experience, these are particularly good heat-resistant varieties: Bibb Buttercrunch, Black Seeded Simpson, Royal Oak Leaf, Jericho (developed in Israel, can you guess?) and Paris Island Cos. Since summer temps in my neck of the woods are typically in the upper 90s to low 100s, these should do OK in most localities.
Germinating lettuce seed in a heat wave isn’t easy. Chilling it in the fridge for about a week first helps, and some people have success germinating it on moist paper tools in the fridge; once you have sprouts, just tear or cut the paper towel and plant right along with the seedling. Outside, germinate in the shade and cover it a little more deeply than you normally would (maybe ½ inch or so). Make sure your soil is loaded with organic material and very finely worked, or cover with potting mix or compost. Soil with a lot of clay tends to bake into a crust in summer heat and the seeds just can’t break through.
I don’t even think about growing summer lettuce in full sun. It does just fine in partly and even fully shaded beds, so that’s where I put it. If you don’t have any shady beds in the veggie garden you might consider growing it in a shady flower bed or in containers you can keep in the shade. You can also use shade cloth or some sort of home-made sun shelter, or grow it on the north side of taller plants. Plant the lettuce closer together than you would if growing to full maturity; it helps shade the roots. Water is obviously extra important in summer. Keep the beds or pots just slightly moist at all times. You can also mist the leaves a couple of times a day, especially if you only have garden beds in full sun.
The most important key to success with summer lettuce is fast growth and early harvest. A steady source of moisture and fertile soil are requirements for most vegetables, but critical for growing summer lettuce. Summer really pushes the lettuce to bolt, so ignore what the seed packet says about days to harvest. Plan to harvest as soon as the leaves are six to eight (at most) inches tall. With the lettuces listed above, you can use the cut-and-come-again method, usually through at least three harvests. Harvest first thing in the morning; the lettuce will usually be sweeter and store better. Take it in and put it in the fridge immediately. Don’t wash until just before you’re ready to use it.
Enjoy your salads!