As temperatures drop and frost threatens your garden, you might think it’s time to pack up your tools and wait for spring. But with a simple, cost-effective structure called a cold frame, you can extend your growing season, protect delicate plants, and even harvest fresh vegetables all winter long.

Whether you’re an experienced gardener or just starting out, building a cold frame is a rewarding DIY project that will boost your garden’s productivity through the colder months. In this guide, we’ll cover everything you need to know—from materials and placement to step-by-step building instructions and what to grow inside your cold frame.

What Is a Cold Frame?

A cold frame is a low, enclosed structure with a transparent top that captures sunlight and traps heat, creating a warmer microclimate inside. Think of it as a miniature, unheated greenhouse—just enough to shield plants from frost, wind, and snow while still letting in light.

Cold frames are ideal for:

• Extending the growing season in fall and early spring
• Overwintering hardy greens and root vegetables
• Starting seedlings earlier in the year
• Protecting potted plants from cold damage

Benefits of Using a Cold Frame

• Grow Winter Greens like spinach, kale, mache, and arugula
• Start Seeds Earlier in spring than you could in open soil
• Harvest in Cold Weather with minimal maintenance
• Low-Cost Alternative to a full greenhouse
• Passive Solar Heating – no electricity needed

Best Crops for Cold Frames

Cold frames are perfect for hardy, cold-tolerant crops. Here are some top choices:

Fall/Winter Crops:

• Spinach
• Kale
• Mache (corn salad)
• Arugula
• Lettuce (winter varieties)
• Radishes
• Carrots
• Green onions
• Swiss chard
• Pak choi and other Asian greens

These vegetables can handle low temperatures and will thrive with just a bit of protection.

Choosing the Right Spot

Where you place your cold frame matters. Consider these tips:

• South-facing exposure is ideal to maximize sunlight
• Sheltered from strong winds to retain heat
• Good drainage is essential—don’t place it in a low spot where water pools
• Close to your home for easy access in winter

Pro Tip: You can build the cold frame directly on garden soil or make it portable to place over raised beds or planters.

Materials You’ll Need:

You don’t need fancy materials to build a cold frame. You can repurpose old windows, doors, or even clear plastic sheets. Here’s a simple materials list:

Frame:

• Untreated wood (2x6s or 2x10s work well)
• Wood screws or nails
• Hinges (if you want a lid that opens)

Top (Lid):

• Reclaimed window or storm door with glass
• Polycarbonate sheeting or heavy-duty clear plastic
• More wood if building your own lid frame

Optional:

• Insulating tape or weather stripping (to seal edges)
• Straw bales or mulch (for extra winter insulation)

How to Build a Simple Cold Frame (Step-by-Step)

Step 1: Build the Base Frame

• Create a rectangular box from wood.
• Standard size: 3–4 feet wide and 6–8 feet long.
• Make the back wall taller (e.g., 12 inches) than the front wall (e.g., 8 inches) so the top slopes downward toward the sun.
• Secure all corners with screws or brackets.

Step 2: Attach the Lid

• Use hinges to attach the transparent top (glass, polycarbonate, or plastic-covered frame).
• Make sure it opens easily for ventilation and harvesting.
• You can prop it open with a stick or add an automatic vent opener.

Step 3: Position It in the Garden

• Place it over prepared soil or raised beds.
• Face it south or southeast for maximum sun exposure.
• Angle the lid to allow rain runoff and optimal light.

Step 4: Add Insulation (Optional for Winter)

• Pile straw or leaves around the outer edges.
• Add insulation strips to the lid to trap more heat.
• Use an old blanket or tarp on freezing nights (just remove it during the day).

Tips for Using Your Cold Frame

1. Ventilate on Sunny Days

Even in winter, it can get surprisingly warm inside a cold frame. Open the lid a few inches on sunny afternoons to prevent overheating.

2. Water Sparingly

Plants in cold frames don’t dry out as fast, so check soil moisture weekly and water only when needed.

3. Monitor Temperatures

Use a thermometer inside the frame to track highs and lows. If it drops below freezing regularly, add extra insulation or use a second layer of cover.

4. Start Small

If you’re new to cold frame gardening, begin with just one and experiment with a few hardy greens before expanding.

Cold Frame vs. Mini Greenhouse: What’s the Difference?

Cold frames are simpler, cheaper, and require no power—perfect for winter veggies and off-grid gardeners.

Final Thoughts

Building a cold frame is one of the smartest investments you can make in your garden. It’s budget-friendly, easy to construct, and can provide fresh, homegrown food even when the snow starts to fall. Whether you’re overwintering spinach or getting a jumpstart on spring lettuce, a cold frame keeps your garden growing when most others have gone to sleep.

So, grab your gardening tools, repurpose that old window, and extend your harvest into the heart of winter—you’ll be amazed at what your garden can do with just a little shelter and sunlight.