Setting Up and Using a Cold Frame to Grow Year Round Lettuce

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There’s nothing like the crisp crunch of fresh, homegrown lettuce in a healthy, vibrant salad. If you’re tired of only being able to grow lettuce in the temperature spring and fall months, it’s time to utilize the power of the cold frame and double the growing season of this yummy veggie. Before you grab some nails and a hammer and get to work, there are a few things you need to keep in mind. Here’s all you need to know to set up and use a cold frame for growing lettuce all winter long. 

Note: Since lettuce is a cool-season crop, and doesn’t do well in temperatures above 80, you may have to take a break for a few months during the summer. Use this time to enjoy other summer vegetables in your garden and prepare the soil for the fall planting season. 

Choose your materials

Whether you buy a premade cold frame or exercise your DIY muscles, you’ll want to pick your materials carefully. Cold frames can be made from several things, including wood, straw bales, bricks, and polycarbonate. Depending on how long you want your cold frame to last and the weather that you’re up against, choose the material that suits your needs best. For instance, colder winters will need something more substantial than polycarbonate, such as wood, to help insulate and keep your lettuce alive through frigid temperatures. 

Remember, the top should be clear and slightly slanted towards the sun. An old shower door or tempered glass patio door works best. Regular windows may be easier to find, but they will often break and leave shattered glass in your crops. Clear plexiglass is also a popular choice since it is lighter and easier to ventilate.

Pick the location

Yes, cold frames are semi-portable, but once they’re full of dirt and healthy plants, they will be virtually impossible to move. Choose an area in your yard that gets adequate sunshine and shelter from the wind. It may be a good idea to consider putting it up against the side of a house, fence, or garage to provide a little extra insulation.

Don’t forget about ventilation

A cold frame is like a smaller, more intense greenhouse. While this is great for keeping the cold air at bay, it can quickly become dangerous for your plants when the temperature starts to rise. Use a stick or other ventilation tool to prop open the cold frame when the daytime temperature is above 40 F. Not only can intense heat burn your crops, but consistent warm temperatures aren’t suitable for cold weather plants such as lettuce. This can lead to soft growth, which won’t be able to withstand the winter chill. 

Maximize the heat

On the other end of the spectrum is making sure that your plants don’t succumb to the frost. Cold winters call for more extreme measures. A few ways to maximize heat in your cold frame include painting the inside white to help reflect heat or lining the edges with aluminum foil for the same purpose. Paint a few gallon milk jugs black and fill them with water. Set them in your cold frame, and they will serve as natural heaters. The jugs will absorb heat during the day and then slowly release it throughout the night, bringing up the internal temperature of the cold frame. 

Keep up on housekeeping

Though you may have to face snowy weather to head out and tend your cold frames, there are still a few tasks that you will need to attend to throughout the winter. Keep your cold frame free of weeds and harvest your lettuce regularly. It is also important to keep the tops cleared of leaves, snow, and other debris. Use your hands or a push broom to wipe off anything that could block the critical sunlight. 

Soil is still important

As you work to prepare your cold frames for the fall and winter planting season, don’t forget the key components of a healthy garden. Light, soil, and water. Soil is particularly essential when you are planting in a raised bed, such as a cold frame. Be sure to amend the soil with plenty of nutrient-rich compost and mix in more as needed. 

What is your favorite thing to grow in a cold frame? Let us know in the comments below!

-Taylor Ramsey

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