Growing Head Lettuce in July
Growing lettuce in the summer can be a challenge since it is usually considered a cool-season crop. However, by selecting heat-tolerant varieties such as Muir or Cherokee Red, it is possible to successfully grow lettuce during the summer months. To get started, consider germinating the seeds indoors either in a north-facing window or using grow lights to provide ample light and warmth for proper seedling development. Most lettuce germinates best around 68ºF, so ambient indoor temperatures are usually perfect. Make sure to water seeds in well and keep covered until you see germination.
If lettuce is stressed, it will signal to itself that it needs to reproduce before conditions deteriorate further. For lettuce, this means flowering, also known as bolting. When lettuce bolts, it releases sesquiterpene lactones, a natural chemical which makes the leaves taste bitter. This bitterness can be mitigated slightly by cooling the lettuce in the fridge as soon as it is harvested, but the best way to avoid a disappointing head lettuce is to prevent as many stressors as possible. In the spring, this is easy as conditions are perfect for most lettuce varieties. However, in the summer, extra steps should be taken to insure a good harvest.
About a week before transplanting our lettuce, we begin to harden it off. When you start seeds indoors, you are giving them the perfect environment in which to thrive. However, the great outdoors is seldom as forgiving, and instead of kicking our seedlings out as soon as they turn 18, we help ease them into the tough reality of the garden. For a couple of days, we leave the seedlings in a shady area, then we move them to an area with partial sun, then finally into full sun for the last few days. This hardening off process is crucial to a successful transplanting, especially in the heat of summer.
When we transplant our lettuce into the field, we do our best to do so in the evening, preferably before a day with clouds in the forecast. We also install 35% shade cloth over the bed to further shield it from the sun. The first 24 hours after transplanting lettuce is when it is most vulnerable. Make sure to give your transplants plenty of water, and amend the soil with a good source of nitrogen like alfalfa meal or blood meal. Once lettuce is established, it is very hands off. As long as you keep it shaded and well watered, you should have decent sized heads within two weeks, and nice full sized heads within a month. During the summer, lettuce will not hold well in the field, so make sure to plant more lettuce every couple of weeks for a consistent supply.
With careful planning and the right techniques, growing lettuce during the summer can yield delicious and crisp results. Remember, maintaining consistent moisture levels and providing adequate air circulation are also key factors in successful summer lettuce cultivation.
