QUESTION: Can you grow lettuce in the summer? When will lettuce bolt? -Jeremy C.
ANSWER: Lettuce is easiest to grow with success in the spring and fall, but with a few precautions you can grow it all summer long, too. Lettuce plants that aren’t heat resistant do best in temperatures between 45 and 75 degrees Fahrenheit. For lettuce plants that thrive in summer, start out with a variety that’s designed to withstand rising temperatures. Look for the phrase “heat-resistant” on the packaging or in the product description, or choose a variety from the list in our answer to the question “What lettuce grows well in summer?” Heat-resistant lettuce plants will persevere longer in hot weather before developing sunscald, wilting, turning bitter, or bolting.
Even heat-resistant lettuces can use a little help to beat the heat, however. Make sure to grow your lettuce in a spot that provides some shade. Lettuce plants need at least six hours of direct sunlight each day, but especially in the afternoon, the protection of some sheltering shade will be welcome. If your yard doesn’t have trees to throw a shadow, you can grow lettuce in the shade of larger plants, like corn, okra, sunflowers, or tomatoes. Shade cloth is another way to give lettuce plants some refuge from the heat.
It may go without saying that you should make sure to provide lettuce plants with plenty of water when it’s hot outside. A consistent supply of ample moisture will not only keep your lettuce plants hydrated but also goes a long way toward keeping them cool. As days get hotter, your plants are likely to require more water than before, especially if they’re growing in containers. Check the moisture level regularly by sticking a finger into the soil near your lettuce plants to see whether the dirt clings to your skin, which means the ground is still moist. While you don’t want to oversaturate the soil, don’t let it dry out completely, either. And schedule your watering sessions in the cool of the morning or in the evening, after the heat of the day has subsided. Hydrating your plants when the sun is blazing overhead is dangerous because the water can get so hot it actually burns their foliage.
Another way to help lettuce plants flourish when the weather is hot that will also reduce how often you have to water them is adding some mulch to your garden. Not only does mulch help the soil retain water, it also keeps the temperature of the soil cooler, therefore protecting the roots of your plants from the summer heat. Just make sure not to allow the mulch to physically touch your plants—allow a margin of empty space around each one of them when you lay the layer of mulch down.
Lettuce seeds germinate best at temperatures below 70 degrees Fahrenheit and can go dormant, failing to germinate, above 85 degrees. That means in the summer, you can’t just sow lettuce seeds into the outdoor garden and hope for the best. Instead, start seeds indoors where it’s cool and the delicate seedlings won’t be scorched. They’ll be ready to transplant into the outdoor garden in four to six weeks. However, it would be quite a shock for your plants to move from the climate-controlled indoors right into the summer sun. To avoid stressing the plants and prevent sunscald, you’ll need to get them accustomed to the outdoor environment gradually using a technique called hardening off. Our article “How and Why to Harden Off Seedlings Before Moving Outdoors” describes exactly how to do this.