Lettuce is one of the most popular vegetables for gardeners, but like most leafy vegetables, lettuce does not do exceptionally well in the summer heat.
In fact, a lot of gardeners completely throw out the idea of growing lettuce in the summer, preferring to plant in early spring or mid/late summer for a fall harvest.
It’s possible to extend your lettuce growing season into the summer, but this involves limiting heat and sun exposure by growing lettuce in more shaded areas of your garden or using shade cloth to block 30-50% of sunlight.
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Can I Grow Lettuce in the Summer?
Even if you live in the tropics, you can grow lettuce in the summer, but it’s more difficult. The reason is that lettuce naturally begins to flower (bolt) in hot temperatures, and that marks the end of the vegetative (leafy growth) phase of its life cycle as the plant focuses on seed production. The key to success, then, is keeping lettuce cool as much as you can in the summer.
What Causes Lettuce to Bolt
Lettuce bolts in hot temperatures, but “hot” to lettuce plants is pretty much normal summer weather in most temperate climates. Typically, when lettuce experiences day temperatures of 75°F (24°C) and night temperatures above 60°F (16°C), it’s only a matter of time before it bolts. If temperatures are even hotter, lettuce and other leafy greens will bolt even faster.
How Do I Know if My Lettuce Is Bolting?
The telltale sign that your lettuce is bolting is when it suddenly gets taller, and new leaves are thinner, smaller, and farther apart. You may also notice a lot more milky, sticky liquid (a type of latex) coming out when you harvest leaves. The leaves themselves will be more bitter, thanks to the milky latex, but are still safe to eat.
Can You Stop Bolting Once It Starts?
It’s impossible to stop it, but you can slow it down by chopping down flowering stalks. This will only give you more time to harvest the existing leaves before they become too bitter.
However, you can significantly slow down the time it takes until your lettuce starts bolting, and I’ll share my tips below on how to get more out of your lettuce in the summer months.
Tips to Successfully Grow Lettuce in the Summer
1. Plant your lettuce in partial shade
If the name of the game is reducing heat exposure, the simplest way to keep your lettuce cool is to grow them in partial shade. While it grows fastest in full sun (6+ hours of direct sun per day), lettuce can thrive in partial shade, which is 3 to 6 hours of sun per day. The only downside is that they will grow a bit more slowly.
The easiest way to grow lettuce in partial shade is by planting them alongside or between other vegetables. For example, you can plant lettuce along the eastern side of a row of tomatoes, giving them plenty of gentle, warm morning sun while giving them shade in the hotter afternoons.
You could also plant them along an east-facing wall or fence or somewhere under dappled shade.
The key is to limit the number of hours of sunlight, which will trigger bolting.
2. Plant lettuce in containers
Planting lettuce in containers will allow you to move your lettuce around when conditions are not favorable.
For instance, if your lettuce is growing in early spring but you’re faced with a sudden heat wave, you can move your lettuce into full shade or even into a garage until it’s over.
I speak from experience: this year we had a few days of summer weather in May, and most of my lettuce, mustard, arugula, and radishes planted in the ground started going to seed later that week. That’s how quickly lettuce can bolt. My lettuce and mustard in containers lasted at least a month longer because I pulled them under the shade on my deck.
3. Grow your lettuce under shade cloth
If you have hot summers or you live in a tropical or desert climate, you can extend your lettuce-growing season by growing them under shade cloth.
Shade cloth is a mesh fabric, usually black or green, which is graded based on how much sunlight it blocks. Typically, shade cloth for gardens or farms blocks 30-50% of sunlight (there are higher grades of shade cloth but they are more often used for shading people). The hotter your climate, the higher the grade of shade cloth needed.