How to Build a Cold Frame to Grow Vegetables in the Winter

Extend your growing season through the winter and learn how to use and build a cold frame for your garden.

Howdy! Mr. TIDBITS here, and today I am going to talk about cold frames for winter gardening. 

WHAT IS A COLD FRAME?

A cold frame is a box with a clear lid that is placed over cold hardy vegetables in your garden to keep them warm enough to continue growing through winter. 

These cold frames can potentially keep your garden plants alive in temperatures below zero and you can have garden fresh salads and vegetables in January. 

The cold frames are designed to keep a pocket of warm air around your cold hardy plants to keep them insulated and growing. 

WHAT ARE COLD FRAMES MADE OUT OF?

Basically, it’s a frame made of wood, straw bales, plastic or anything strong enough to hold together and be somewhat of an insulator. The frame is topped with a clear cover made of glass, plastic or fiberglass and strong enough to support several inches of snow. 

HOW DO COLD FRAMES WORK TO KEEP MY VEGETABLES ALIVE DURING WINTER?

When the cold frame box sits over the plants you are trying to protect them from freezing temperatures and still allow the light to enter. 

Basically, it’s a miniature greenhouse for your plants.  You can even use a cold frame to get your seedlings started outside earlier in the year. 

HOW TO BUILD A COLD FRAME OUT OF WOOD AND CLEAR PLASTIC

You may recall, last year we built some raised bed planters to grow vegetables near our house and shared the plans for those.  Now we have some plans for cold frames to sit on top of those raised beds.

You can always adapt the measurements to suit your own garden beds or anywhere in your garden which you plan to cover with cold frames. 

They are very simple to build and take only a few minutes to put together. 

SUPPLIES NEEDED TO BUILD A COLD FRAME

• 2x6x8 boards preferably treated or cedar – need 2
• 1x4x8 board – need 1
• 1x4x10 board – need 1
• Clear PVC roof panel – need 1
• Screws or nails to assemble
• Clear caulk
• Handle (optional)

I bought pressure treated boards so they can withstand the elements.  The boards do not touch the ground or plants, so I am not concerned about contamination from chemicals.  Cedar would be the best option if you can afford it. Start by cutting the 2x6x8 boards into these dimensions:

• 70 inches – need 2
• 26 inches – need 2

Screw or nail them together to form a box with the short pieces between the long pieces so the inside dimension of the box is 26 inches wide x 67 inches long.

Next cut the 1 inch thick boards to the following dimensions.

• 66 1/2″ long – need 2
• 24 1/2″ long – need 3

Staple, screw or nail the two long boards on the inside of the box about 3/4″ inch down from the top of the box.

Next staple, screw or nail the three short boards between the two long boards at the ends of the box and one in the middle for added support.

Cut the clear PVC roofing panel to length and it should slide inside of the box to rest on the 1″ thick boards.

Use screws to attach the roofing panel to the 1″ boards.

Finally caulk the edges of the panel to create a seal that will help keep the warm air in.

I attached handles to make it easier to prop the boxes open on warm days. This is optional but highly recommended.

WHAT YOU NEED TO KNOW ABOUT USING COLD FRAMES

A few things to note about cold frames.

• If the temperature gets above 50° during the day, then you will need to prop these open until temperatures drop as it can get too hot inside the frames and damage your plants. 
• Do not brush the snow off the tops, light will still penetrate just fine, and the added snow will create more insulation.
• Only open if the temperature outside is above freezing.  When you open the boxes all the heat will escape, and you need to be sure there is enough sunshine to warm the box back up before nightfall.  Plan your harvesting trips so that you can harvest what you need for several days and keep the boxes closed as much as possible. 

WHAT TYPES OF PLANTS CAN YOU GROW IN THE WINTER WITH COLD FRAMES?

Cold hardy plants are the only ones that will grow in a cold frame.  This can be plants such as:

• lettuce
• arugula
• carrots
• peas
• radishes
• spinach

Again you have to choose the cold hardy varieties of these plants since there are some lettuce plants that are more warm friendly. 

Plants such as tomatoes or melons will not survive in a cold frame. Although they keep warm air inside the box, they will not be warm enough for these types of plants. 

I hope this helps you keep your garden alive as winter approaches and enjoy those fresh salads through the cold season. 

This is a new adventure of learning for us, so hopefully we can report back through the winter and share what worked and what didn’t.

Make sure to come back for more inspiration for the keeper of the home.