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DIY Mini Greenhouse (Cold frame)

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Want to grow fresh vegetables all winter long? Consider building a DIY Cold frame or mini greenhouse from old windows. A cold frame acts just like a greenhouse, but on a smaller scale. Grow fresh food, even if the ground around it is covered in snow! This will take your winter gardening to a whole new level!

mini greenhouse

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Building a Cold frame

When the hubby and I first got married, he wasn’t exactly the handiest guy around. His power tools at the time consisted of a drill. He recently told me, after installing some fabulous tile floors, that he just didn’t NEED to know how to do handy tasks before marriage. Rest assured, I always seem to have some sort of project waiting for him to tackle. And I think because of my ever-growing “Honey do” list, his abilities with wood and power tools (which he has quite a few more of now) have grown by leaps and bounds. I’ll take some credit for that…

I may have mentioned before that I occasionally like to pick up roadside treasure and bring it home with big ideas for its future. Sometimes these plans don’t always work out. Case in point, an old console tv that I was going to turn into a bookshelf… never happened. Tearing the tv component out of a cabinet is much harder than it looks. My hubs is not usually a fan of my “projects” since not all of them reach completion.

So, you can imagine my surprise when one afternoon he actually tells me, “Hey, the neighbor put out the old windows he just had replaced.” Say what?? Of course, I told him to grab them! He snapped them up off the side of the road and built me this fab little greenhouse within days. It’s true… I couldn’t believe it either.

While this wasn’t the first window cold frame he has built, it is certainly the largest. The first was made from one standard wood window on a simple angled frame. The sides and back were covered in plastic sheeting. While it wasn’t the prettiest, it certainly did the job of keeping in the heat for little seedlings to grow.

Cold frame vs. Greenhouse

A cold frame is basically a simple structure that uses heat from the sun to create a small microclimate within a space. If you think about leaving your car out in the sun on a winter’s day, you’ll find that the sun itself will warm your car despite the cold temperatures. This is the same way a coldframe operates.

A greenhouse technically needs both walls and a roof made of glass or another transparent material. So while this project isn’t a technical “greenhouse,” many newer gardeners recognize this word. And since both greenhouses and cold frames are providing a small warm climate, I’m using them a bit interchangeably here. (Looking for a ready-to-go greenhouse? Check out my review of the Abba Patio Greenhouse kit here.)

Why Use a Cold frame?

There are many reasons to use a cold frame in the garden, and these can include:

  • Starting seeds outdoors (not everyone has tons of room inside for starting seed)
  • Overwintering plants that go dormant in winter
  • Having a bit longer growing season

What You’ll Need:

(Project is based on 80″x24″ windows, but can be modified to fit your window size.)

2 wood framed windows (find them on the side of the road, flea markets, craigslist, etc.)

2 Cedar- 1×6’s (Quantity depends on the size of your windows)

1×4 (wood of choice-length of the window)

2×2 (wood of choice)

4-6 hinges with hardware

2 handles with hardware

scrap metal, scrap wood, or plastic sheeting for ends

How to Build a Cold frame at Home

1.Your first step is to attach the windows to the 1×4 board that will be the top of your cold frame. To do this, lay your windows on the ground with the 1×4 (cut to window length). Place hinges on windows and board, so you’re sure to have enough space for the windows to move once the hinges are screwed in. Mark screw holes in hinges with a pencil on wood. Once you’ve determined where each hinge will be, attach hinges with included hardware. mini greenhouse

2. Now stand your windows up (bottom edge resting on the ground) to determine how large of a “box” you want your frame resting on. If you want the coldframe to accommodate taller plants, you’ll want a box with less width. If you’re not worried about height, but would like a wider box to fit in more small plants, then spread your windows further apart. The idea is to play around with your attached windows and figure out what size space you’d like covered by your coldframe. (We settled on a taller frame, so I could use it for a variety of plants.) Once you’ve determined how you want your windows situated, measure the distance between the corners of the windows for your box width. Your box length will be the length of the window.

3. Using the width and length measurements you’ve taken, use the 1×6 cedar boards and create your “box.” Once you have your 4 sides (2 width wide boards, 2 length wise boards) attach them using L-shaped connectors. (This simple box you’ve created would also be an easy way to make a raised garden bed.)mini greenhouse

4. Using your 2×2’s you’ll now create the frames for the ends of your box. These will hold up your windows and 1×4 connector piece. First, cut pieces to attach to the ends of your 1×4 connector board. These pieces will have angled ends, so your windows will have a place to rest and not collapse in. Our pieces were 5 inches on the top and 6 1/2 inches across the bottom. Cut four pieces this size; you’ll use two now and two later. Once you have your pieces cut, screw one onto each end of the 1×4 board that’s attached to your windows. mini greenhouse

5. Now you’ll create the edges of your end pieces. (The end pieces of your cold frame are essentially triangles with flat tops. You’ve just attached the flat tops to your 1×4 connector, now you’re making the sides of the triangle.) For this, we cut 2×2 boards into 21 1/4 inch pieces with angled ends. You’ll need 4 of these pieces, two for each end of the frame. Since the 2×2 pieces will sit at an angle, you’ll need to cut the ends slightly, so they will fit flush against your top piece and your box at the bottom. Once you know the pieces fit against both the top board and bottom box, screw them into place. mini greenhouse

6. Because of the size and weight of the windows we were using, we also added pieces of 2×2 to the middle of the end frames. We cut two 22-inch pieces and attached one at each end of the frame, between the side pieces we’d just attached. (These pieces screwed into the 1×4 at the top and into the inside of the box end. (See above image.)

7. Almost done! For smaller windows, this next step won’t be necessary, but for additional support, we added angled 2×2 pieces to give the 1×4 connector extra strength. You cut these pieces earlier in Step Four. Take those two angled pieces you cut, and fit them between the 2×2 at the center of your end piece and the underside of the 1×4. Once you have them in place, screw them in. mini greenhouse

8. You’ll want to cover the open ends of your cold frame. You can do this with any scraps you have laying around. We used some sheet metal left over from a different project. Simply cut the scrap to size and attach it. You could also wrap the ends of your cold frame with plastic sheeting and staple into place. Either way works!

9. As a final step, attach handles to the bottoms of your window frames. This will give you an easy way to open your cold frame. And you’re done!

mini greenhouse

While this project may seem like a lot of steps, it’s totally worth it to extend your growing season and be able to start seedlings outdoors. Once our frame was finished, I painted the 1×4 connecting the two windows just to make it more weather-resistant. If you use a cedar 1×4, you could probably skip this. All window sizes can work for this project, you’ll just need to measurement and adjust.

I have our cold frame sitting on a raised bed with dormant strawberries just waiting for a touch of warmer weather. I’d love to know if you’ve had success using cold frames in the garden!

Yield: 1 Cold Frame

DIY Cold Frame (Mini-Greenhouse)

mini greenhouse

Use old windows to create a cold frame that will allow you to garden all winter long.

Prep Time 30 minutes
Active Time 3 hours
Total Time 3 hours 30 minutes
Difficulty Moderate

Materials

  • 2 wood framed windows (find them on the side of the road, flea markets, craigslist, etc.)
  • 2 Cedar- 1x6's (Quantity depends on the size of your windows)
  • 1x4 (wood of choice-length of the window)
  • 2x2 (wood of choice)
  • 4-6 hinges with hardware
  • 2 handles with hardware
  • scrap metal, scrap wood, or plastic sheeting for ends

Tools

  • Drill
  • Saw (for cutting wood)

Instructions

    1. Attach the windows to the 1x4 board that will be the top of your cold frame. To do this, lay your windows on the ground with the 1x4 (cut to window length). Place hinges on windows and board, so you're sure to have enough space for the windows to move once the hinges are screwed in. Mark screw holes in hinges with a pencil on wood. Once you've determined where each hinge will be, attach hinges with included hardware.
    2. Stand your windows up (bottom edge resting on the ground) to determine how large of a "box" you want your frame resting on. If you want the cold frame to accommodate taller plants, you'll want a box with less width. If you're not worried about height, but would like a wider box to fit in more small plants, then spread your windows further apart. The idea is to play around with your attached windows and figure out what size space you'd like covered by your cold frame. (We settled on a taller frame, so I could use it for a variety of plants.) Once you've determined how you want your windows situated, measure the distance between the corners of the windows for your box width. Your box length will be the length of the window.
    3. Using the width and length measurements you've taken, use the 1x6 cedar boards and create your "box." Once you have your 4 sides (2 width wide boards, 2 length wise boards) attach them using L-shaped connectors. (This simple box you've created would also be an easy way to make a raised garden bed.)
    4. Using your 2x2's you'll now create the frames for the ends of your box. These will hold up your windows and 1x4 connector piece. First, cut pieces to attach to the ends of your 1x4 connector board. These pieces will have angled ends, so your windows will have a place to rest and not collapse in. Our pieces were 5 inches on the top and 6 1/2 inches across the bottom. Cut four pieces this size; you'll use two now and two later. Once you have your pieces cut, screw one onto each end of the 1x4 board that's attached to your windows. 
    5. Now create the edges of your end pieces. (The end pieces of your cold frame are essentially triangles with flat tops. You've just attached the flat tops to your 1x4 connector, now you're making the sides of the triangle.) For this, we cut 2x2 boards into 21 1/4 inch pieces with angled ends. You'll need 4 of these pieces, two for each end of the frame. Since the 2x2 pieces will sit at an angle, you'll need to cut the ends slightly, so they will fit flush against your top piece and your box at the bottom. Once you know the pieces fit against both the top board and bottom box, screw them into place. 
    6. Because of the size and weight of the windows we were using, we also added pieces of 2x2 to the middle of the end frames. We cut two 22-inch pieces and attached one at each end of the frame, between the side pieces we'd just attached. (These pieces screwed into the 1x4 at the top and into the inside of the box end. (See above image.)
    7. Almost done! For smaller windows, this next step won't be necessary, but for additional support, we added angled 2x2 pieces to give the 1x4 connector extra strength. You cut these pieces earlier in Step Four. Take those two angled pieces you cut, and fit them between the 2x2 at the center of your end piece and the underside of the 1x4. Once you have them in place, screw them in. 
    8. Now cover the open ends of your cold frame. You can do this with any scraps you have laying around. We used some sheet metal left over from a different project. Simply cut the scrap to size and attach it. You could also wrap the ends of your cold frame with plastic sheeting and staple into place. Either way works!
    9. As a final step, attach handles to the bottoms of your window frames. This will give you an easy way to open your cold frame. And you're done!

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