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How to Build a Cold Frame Container Garden for Winter

For manufactured homeowners, or really anyone wanting to grow greens in the winter, follow this cold frame tutorial! Start seedlings early before spring hits or extend your fall harvest.

Crisp kale, savory bok choy, and tasty arugula are all great when they are fresh from the garden in the summer, but how good would they taste in winter?

Enter the endless possibilities of a cold frame. A cold frame container is perfect for extending your fall growing season or starting seedlings in late winter. 

What Is a Cold Frame?

A cold frame is really just a mini greenhouse. By protecting your plants from excess cold and frost, a cold frame extends the growing season of greens and herbs.

I plan on maintaining and re-growing greens from scraps in this particular cold frame, but it can be your home to a whole host of vegetables. It's a great project for container gardening enthusiasts.

Charlie's Build Your Own Cold Frame Project

This cold frame is uniquely designed for manufactured homeowners who rent land in a manufactured home community, apartment dwellers with porches or anyone else who has access to the outdoors but does not want to dig up a garden.

By using a reclaimed window and the right finish, this project makes a great shabby-chic addition to any country style home or apartment!

If you have a family member or friend with a work shop, this would be a good project in which to include them (and use their space). However, this can certainly be built in a weekend with a little patience and a comfortable work area.

Tool list:

  • Cordless drill
  • A good hand saw
  • Surform (for minor adjustments after cuts)
  • Framing square
  • Speed Square
  • 4 bar clamps

Parts List:

  • 3 1”x6” boards at 6ft.
  • 1 1”x4” board at 6ft.
  • 2 2”x4” studs at 8ft.
  • 1 2x2 foot section of ¼ in. plywood
  • A box of 2¾ in. drywall screws
  • Wood stain of your choice
  • Two door hinges and a pull handle
  • Reclaimed window with non-lead paint

Step 1. Build The Growing Box Frame For Your Window

My window (acquired at a Habitat for Humanity ReStore) happened to be 26 ¼ in. by 19 ¼ in. So, I built a bottom layer of the box with the 1”x6” stock to those dimensions.

Now for the trickiest part of this build. To build the “top layer” of the growing box, you’ll need to cut a taper on the two shortest sides. This is so you can angle the box south, where it will get the most sun on short fall and winter days.

If you have a jig saw or table saw, you won’t have any problem. I don’t own either, so I just used a handsaw.

Start by putting a mark 4 in. from the edge of a 1"x6" board.

Then, use your framing square to draw a line from the other edge to that point, as pictured below.

Now, clamp your board against a bench or in a vise and start sawing, paying extra close attention to the beginning part of the cut. If you get a good start and focus on cutting on the line, you should have no trouble cutting these two pieces out.

Step 2. Cut the Legs

A standard workbench is around 30 in. high. I’m a little taller than most, so I went with 36 in. legs for comfortable cutting without bending over.

Cut four legs at 2 in. less than your desired height.

Next, clamp the legs to rest 8 in. into your box from the bottom. With screws, attach the box to the legs to make sure the legs are attached to the two “layers” of the boxes.

Step 3. Install the Bottom

At this point, you should have something that looks like the picture below.

Now it’s time to put in a bottom. I only plan on having a few small pots of herbs and greens in my cold frame, so I went with ¼ in. plywood. You can upgrade to ½ in. or thicker as you see fit.

Start by making corner brackets from your 1"x6" scraps with a square.

Then, measure and cut two 2”x4” studs to brace the inside of the box and add more surface area to attach the floor.

Put a bead of glue around the 90° corner of the bracket and attach with screws to the 2”x4” brace and the leg.

Finally, using a framing square, plot and saw the dimensions of your plywood to lay flush with the sides.

You can glue it down, but it is not necessary as long as the brackets are properly braced.

Step 4. Install Window and Finish

If you have done everything right, your window should rest flush on the box. Find where you want your hinges and install them on the back using their hardware.

On the front, find your center point and install the pull handle there.

Finally, stain and finish your wood frame with whatever color you like. Since this box will be exposed to the elements, it’s essential to use a natural finish like linseed oil or polyurethane sealant to protect the wood and stain.

Using your Cold Frame

There are lots of different ways to use this cold frame. Look at different growing resources for winter growing tips depending what kind of plants you want to grow in your cold frame!

However, there are a few best practices.

  • For one, use a wooden dowel or scrap wood to prop the door open when a day is going to get above 70° to allow proper ventilation.
  • Second, face the front of the box south. The afternoon sun is the longest, so the designed taper will expose your plants to more life giving sunshine.
  • Finally, remember to use your cold frame in early spring. March, and sometimes April depending where you live, always brings a final frost that can kill the hardiest of seedlings, so start small plants in the cold frame until the final frost happens. This gives you a longer growing season into the summer!

Now that you've prepped yourself for growing veggies this winter and for starting seedlings in the early spring, start planning how you'll get your lawn ready for spring. Early spring is a great time to start planning out your garden projects.

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