Heat Tolerant Lettuce
Inside: Growing lettuce in the summer can be tricky. These tips and tricks plus heat tolerant lettuce varieties will help you extend your harvest into the summer growing season.
Every year at the height of salad season, just as the tomatoes start to ripen, my lovely homegrown lettuce decides to give up and go to seed. And it’s always sad.
One day I’ll pick a lovely head of sweet romaine from the garden. Two days later, when I go to pick another head, I’ll taste the lettuce and instead of sweet, I taste bitter undertones.
Why does lettuce do this to me? Just as all the other produce is starting to ripen? Well, lettuce is a cool season vegetable. It much prefers the cooler temperatures of spring and fall.
Is there anything that can be done to prolong the harvest? Can you grow lettuce (and other leafy greens) all summer?
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Can You Grow Lettuce All Summer Outside?
Maybe, but it will require some work on your part unless you live in a very cool climate or grow lettuce indoors. And if you live where you CAN grow lettuce all summer, you likely don’t have the climate to grow tomatoes and squash then.
Can You Prolong the Harvest?
But there are some things you can do to prolong the harvest. I’ll cover some of these options below.
Water Your Lettuce Often
Lettuce will quickly turn bitter and bolt (send up a flower stalk to produce seeds) without adequate water. Keeping your lettuce watered is the number one thing you can do to prolong the harvest. In addition, the water also helps to cool the roots which will keep it from bolting as quickly too.
Mulch Heavily
Provide lots of organic mulch around your lettuce. Just like frequent water helps, mulch will hold that water in the ground longer and keep the soil temperature down and the roots of the lettuce cool.
Use a Shade Cloth
One of the easiest ways to grow lettuce longer is to cover the lettuce with shade cloth when the temperature rises above 80. Shade cloth helps to reduce evaporation and keep the lettuce cool.
Whether you’ve grown lettuce in the ground, raised beds, or in a container, a bit of shade cloth covering the plants will help it last longer. I recommend using shade cloth with a minimum coverage of 40% but any kind will help.
Grow Lettuce in Containers
Growing summer lettuce in containers means you can move the lettuce to the shade when the temperatures soar. Be sure to choose a container that isn’t too large to move though! If your container is too big to move, try covering the container with shade cloth.
The best way to have healthy lettuce plants is to allow the plants some morning sun and then move the plants to afternoon shade. Most lettuce varieties do need some sun to produce their best, but it doesn’t have to be full sun.
Choose Heat-Tolerant Varieties of Lettuce
Some varieties of lettuce seem to handle the cold of winter better while some lettuces are bred to last longer in the heat. Choosing these heat-resistant varieties will help you extend your spring salads into the summer.
Best Heat-Tolerant Lettuce Cultivars
These varieties listed below are MORE HEAT TOLERANT than others. This doesn’t mean they will survive all summer. (But I’ve got a few tricks below that will help you harvest lettuce all summer.)
- Jericho is a romaine type lettuce bred in Egypt to stand up to the heat.
- Parris Island Cos is another romaine lettuce suited to hot weather.
- And if you are looking for an heirloom variety, Ice Queen is a heat tolerant romaine to try.
- Buttercrunch is a favorite type of butterhead lettuce that will do well in the heat. It produces a dark green head of lettuce and is slow to bolt.
- Red Sails is a beautiful red variety of leaf lettuce that tolerates hot weather well.
- Black Seeded Simpson is another leaf lettuce and a long time gardener’s favorite lettuce for its reliable production.
Read How To Grow Lettuce for more information.
I personally have had the best success with loose-leaf lettuces like Red Sails and Black Seeded Simpson. Picked early and often, they keep providing me with salads through most of the summer.
I recently discovered Simpson Elite and it has held off bolting the longest for me. Other different lettuce varieties that you might want to try include Deer Tongue, Oakleaf, and New Red Fire.
Just remember that the heat tolerance of lettuce can vary due to micro climates. So pick up a couple of different seed packets of some lettuce types that sound promising and give them a try.
Start New Plants
Another tip I want to share is to succession plant your lettuce. Start new lettuce seeds every 2-3 weeks. Ideally, start them indoors under grow lights for best results. It can be difficult to get lettuce to germinate in the heat.
If you do decide to sow your lettuce by direct seeding into the garden bed, be sure to keep it well-watered.
I like to start my seeds in Jiffy pellets as they greatly reduce the transplant shock. (Shop around. You can usually find the best prices by buying locally.) However, before you move your seedlings outdoors to the garden or a container, be sure you harden your seedlings off properly.
Planting lettuce outside in the hot sun after the plants have led a pampered life indoors is a recipe for disaster if your seedlings aren’t properly prepared.
And when you do transplant them outdoors, be sure to water them regularly, mulch heavily, and if possible cover them with a shade cloth to help them acclimate to the outdoors.
Harvest Your Lettuce Frequently
Finally, harvest your lettuce early and often. If you keep harvesting as baby greens, the lettuce doesn’t have as much chance to get large and bitter or bolt.
Remember to pick the outer leaves so that the new leaves can keep growing from the center of the plant.
Choose Other Heat-Tolerant Greens
If you truly want to eat salads all summer, try a different type of green. Swiss chard can usually be harvested throughout the warmer temperatures of summer. If you plant enough you can harvest the leaves as baby greens for a salad or sandwiches.
Another leafy vegetable to try is edible red leaf amaranth. This variety actually likes the hot temperatures and will grow most of the summer season.
Many amaranth varieties are native to Mexico and the southern United States so they can tolerate high temperatures, but red leaf amaranth is the most suitable for eating as a leafy crop. The red leaves taste a bit like spinach with a bit of a tang to them.
So choose heat tolerant lettuce varieties. Keep your lettuce watered and mulched. Harvest often. And who knows, you may just be able to grow fresh lettuce all summer long.
