Heat is the bitter enemy of lettuce.
Want to grow your own lettuce? Check out How To Grow Your Own Gourmet Lettuce from Seed - It's Easier than You Think!
Our weather is unpredictable year round—and from each year to the next—but one thing is certain: there is always at least one heat wave in April. A few days in the upper 90s are not uncommon. With soaring temperatures (88F Wednesday, 91°F yesterday) and more predicted through the week, I realized it was already time to shade the lettuce bed.
Just a few days of extreme heat can transform your entire crop of lovely lettuce into bitter greens—and send it bolting skyward with nothing but seed making on its mind.
Even a little bit of shade can make a big difference for nearly all plants. Full sun is harsh. If the thermometer reads 90°, a plant or person standing out in the sun for any period of time is going to feel much hotter than that.
Even heat tolerant, sun loving plants like tomatoes and peppers can do with some time in the shade. Most plants that need 'full sun' only require 6 hours of sunlight a day. If they're getting more like 12, they can easily become stressed
Several years ago I read about a couple who had quit their jobs at a large newspaper, moved to the country, and created a wildly successful small farm business. They sold their bounty at a farmers' market and through weekly subscriptions (conveniently to all of their former colleagues—one delivery stop and they were done).
One of their most popular crops was basil, which does just fine in the heat. So when this couple spent $1,400 constructing a greenhouse solely to house their summer basil plantings, people thought they were nuts—until they saw the results. The greenhouse basil was bigger, healthier, and tastier than what they had been growing in direct sunlight.
Soon I'll be tying an inexpensive, blue plastic tarp over the top of my greenhouse to keep the interior temperature down. Click here to see a photo. I also keep the door open and back side vented. Even with the tarp on, plenty of light still reaches the plants.
The raspberry canes growing on the south side also create shade and help cool things down. Some people roll up the sides of their greenhouse plastic in summer so the air can flow through, which is what I plan to do with my next greenhouse. Others remove it entirely and replace it with shade cloth.
But back to the lettuce, which I don't plant in the greenhouse in spring because even now it's already too warm in there. Creating indirect light for your plants using a greenhouse, shade cloth, or by simply growing them in a partly shaded spot can make all the difference. Just think of how well everything grows in mostly cloudly places like England and the Pacific Northwest. Cooling down your heat hating lettuce can literally save or extend your crop.
You can buy fairly inexpensive rolls of weather resistant shade cloth in garden centers and nurseries or by mail order. Or you can poke around the house/garage/basement/neighbor's yard and see what you already have hanging around.
Old bedsheets (check thrift stores and yard sales) offer many of uses in the garden, including as shade makers. Clip them (clothespins work) to bamboo stakes (or old broomsticks or your kids' hockey sticks or whatever you can find) stuck into the ground around your plot. Just remember to take them down if it rains.
My 'shade cloth' in this photo consists of two strange curtains I found stashed in an old storage box. They still let in a fair amount of sunlight, but they also allow the rain to reach the plants so I can just leave them up all the time. And after three years out in the blazing sun, they haven't begun to disintegrate, which is a bit frightening actually.
The obnoxiously bright but easy to spot plastic clips were purchased at a discount store on a whim and have come in very handy around the garden.
For more information about the mini greenhouse frame on this lettuce plot, please see the comments section in this previous post.
One more tip to please your plants:
Regular watering during hot days is, of course, essential, especially if you're growing in containers. Raised beds also dry out faster than regular garden beds. Supposedly by the time a plant shows signs of wilting, it is already in extreme distress.
Note: Unless you live in the Southern U.S. or other warm climate, it's not too late to get a little gourmet salad garden going. Check out my post, How To Grow Your Own Gourmet Lettuce from Seed - It's Easier than You Think!, for inspiration and tips.