Extending Your Growing Season: The Power of Cold Frames

Ashleigh Smith + photo

Ashleigh Smith

Oct 11
5 min read
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garden cold frame
Chelsea Hafer Written By Chelsea Hafer

Gardening has come a long way, but some old-school techniques remain as valuable as ever. One such technique is the use of cold frames, a vintage season-extending tool that's been employed by gardeners for generations. In this guide, we'll explore what cold frames are, why you should consider using them, and how you can build your own DIY cold frame or opt for a more professional setup. Plus, we'll reveal the benefits of using cold frames and suggest some seeds you can plant under them in the fall or early spring.

What Are Cold Frames and Why Use Them?

Cold frames are like mini greenhouses, allowing you to harness the power of the sun to create a warm, protected environment for your plants. These structures consist of open-bottom boxes, typically made of wood, with a clear lid that lets in sunlight. The sun heats the interior, providing several degrees of frost protection, extending your growing season by one to three months.

Cold frames offer various advantages. They're perfect for hardening off seedlings in the spring, growing cool-season crops in late fall and early winter, and overwintering tender plants. They can also help you get an early start on spring planting. Let's dive into how you can build your own cold frame.

opening cold frame

Building A DIY Cold Frame

Constructing a DIY cold frame is a straightforward project that doesn't require fancy materials or tools. Here's how to do it:

  • Gather Materials - You'll need wooden boards, screws, hinges, and a transparent cover. Old windows or fiberglass panels work well for the cover. Make sure to use weather-resistant wood, and avoid treated wood.
  • Design the Frame - Create an open-bottom wooden box with a sloped lid. The back (north side) should be higher than the front to capture more sunlight. A 12-inch front height with an 18-inch back height is a good starting point.
  • Assemble the Box - Screw the wooden boards together to form the box, ensuring it's sturdy and level.
  • Add the Lid - Attach hinges to the back of the frame and the cover to allow you to open and close it easily.
  • Paint the Interior White - Painting the inside of the frame white reflects more light onto your plants.
  • Prepare the Bed - Dig out the area where you'll place your cold frame, about 12 inches deep. Add gravel or sand for drainage, then fill with fertile soil.
  • Place the Cold Frame - Place the Cold Frame: Set your frame on top of the prepared bed, sinking it 4-8 inches into the ground for added insulation.

Taking Season Extension Further

Cold frames can significantly extend your gardening season and help you grow a variety of crops. To get the best results, here are some tips and insights on using these miniature greenhouses effectively:

Ideal Location - Choose a well-drained site that doesn't flood during heavy rains. Position your frames for maximum exposure to winter sunlight, ideally with a southern exposure. Wind protection from the north and west is essential to maintain the interior temperature.

Smart Construction - When you're building a cold frame, construct it with weather-resistant materials. Wooden frames are common, but materials like brick, cinder blocks, and concrete offer durability. Ensure the lid is attached with hinges for easy access.

Size Matters - Determine the size of your frame based on your needs and the materials you have available. Generally, a 3x6 foot frames provides plenty of space while allowing easy access to all corners. If using old windows, use their dimensions for the frame size.

Proper Bed Preparation - Prepare the bed inside the frame with good drainage. Fill it with fertile soil.

Temperature Management - Be mindful of temperature fluctuations inside the frames. On sunny days, the temperature can rise quickly, so prop open the lid to release excess heat. Close the lid by late afternoon to retain warmth for the night. For cold nights, consider adding insulation, such as blankets or poly-styrene boards.

Choose the Right Crops - In cold frames, grow quick-growing, cold-tolerant crops like lettuce, spinach, endive, and herbs. These can thrive into the winter months.

Proper Watering - Monitor moisture levels regularly, as both cold frames have specific water needs. The airtight design of cold frames reduces evaporation. Keep the soil consistently moist but not waterlogged.

Overwintering and Storage - Besides season extension, cold frames can be used for storing tender ornamentals, potted bulbs, or rooting hardwood cuttings.

If you want to extend your growing season even more, you can explore other options like hot beds, hoop houses, cloches, and floating row covers. Each of these methods has its unique advantages and uses, depending on your gardening goals and climate.

As you delve into season extension techniques, don't forget to embrace the vintage wisdom of cold frames. By harnessing the sun's energy and creating a cozy microclimate for your plants, you can enjoy homegrown produce well beyond the typical growing season. So, roll up your sleeves, build a cold frame, and savor fresh veggies even when there's a chill in the air. Happy gardening!

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