Why Build a Cold Frame from Old Windows?
Extending your vegetable harvest into winter doesn’t require expensive greenhouse kits. A cold frame old windows project lets you repurpose salvaged materials into a sturdy, effective season extender. Cold frames trap solar heat and protect plants from frost, allowing you to grow cold-hardy greens like kale, spinach, and mache well past the first freeze. This guide will walk you through building your own using recycled windows.
Materials and Tools You’ll Need
Before you start, gather the following items. Most can be sourced from salvage yards, Habitat for Humanity ReStores, or your own basement.
Materials
- Old window (single or double pane, wood or aluminum frame) – measure your available space; a typical size is 24–36 inches wide, 36–48 inches long.
- Lumber for the frame base: pressure-treated 2×6 or 2×8 boards (cedar or redwood are rot-resistant).
- Hinges: 2 heavy-duty strap hinges (galvanized or stainless steel).
- Screws: 3-inch deck screws for the base, 1-inch screws for hinges.
- Weatherstripping: foam tape or rubber seal to insulate the window-to-frame gap.
- Optional: polycarbonate sheet or glass for a second pane if you want double-glazing.
Tools
- Measuring tape
- Circular saw or handsaw
- Drill with screwdriver bits
- Level
- Clamps (optional but helpful)
Step-by-Step Building Instructions
1. Measure and Cut the Base Frame
- Place your cold frame old windows on a flat surface. Measure the exact width and length.
- Cut four pieces of 2×6 lumber: two sides (length of window + 3 inches for overlap) and two ends (width of window + 3 inches). The extra inch allows for a lip to hold the window in place.
- For example, if your window is 24×36 inches, cut two 39-inch pieces for sides and two 27-inch pieces for ends.
2. Assemble the Base
- Arrange the boards into a rectangle. The sides should overlap the ends (butt joint).
- Drill pilot holes and secure with 3-inch deck screws at each corner. Use two screws per joint.
- Check corners with a level to ensure they are square. Adjust before final tightening.
3. Attach the Window
- Place the assembled base on a level spot in your garden. Position the window on top, centered so there’s a 1-inch lip all around.
- Attach the hinges to the back edge of the base (long side). Screw the hinges into the base first, then into the window frame. Use 1-inch screws for the window side to avoid cracking the glass.
- Test the lid: it should open and close smoothly. If it sticks, adjust hinge placement.
4. Add Weatherstripping and Finishing Touches
- Apply foam weatherstripping along the top edge of the base where the window rests. This seals the gap and retains heat.
- Optionally, paint or stain the wood to protect against moisture. Use exterior-grade paint.
- If you live in a windy area, add a hook and eye latch to keep the lid closed.
Positioning and Using Your Cold Frame
Location
- Place the cold frame in a sunny spot, south-facing if possible. Ensure it gets at least 6 hours of direct sun in winter.
- To maximize heat absorption, tilt the frame slightly south by digging the back edge into the ground 2–3 inches deeper than the front. This also helps rainwater runoff.
Planting and Care
- Which vegetables? Cold-hardy greens like spinach, kale, arugula, mache, and winter lettuce. Also try root vegetables like carrots or radishes if you have depth.
- When to start? Sow seeds in late summer or early fall (August–September in most zones). For a winter harvest, transplant seedlings into the cold frame in October.
- Ventilation: On sunny winter days, temperatures inside can soar above 80°F. Prop the window open an inch or two to prevent overheating and excess humidity. Open fully on mild days above 45°F.
- Insulation: For extreme cold (below 20°F), cover the cold frame at night with an old blanket or bubble wrap. Leave a small gap for ventilation.
Seasonal Maintenance
- Snow load: Brush light snow off the window to prevent breakage. Heavy snow can be left as insulation, but remove if weight is a concern.
- Cleaning: Wipe the glass periodically to maximize light transmission. Use a mild vinegar solution.
- Weed and pest control: Check under the frame for slugs or weeds. Handpick any pests.
Practical Takeaway
Building a cold frame old windows is a weekend project that pays off all winter with fresh greens. The key steps: measure your window, build a wooden base, attach hinges, and seal with weatherstripping. Position it south-facing and vent on sunny days. With minimal maintenance, you’ll harvest from November through March.