Extend Your Growing Season with a DIY Cold Frame

Ready to extend your growing season with a DIY cold frame?

Adding a cold frame to existing raised beds allows you to grow more food, for a longer period of time. Protect your lettuce, chard, spinach, kale and other greens from winter frost by covering with a DIY cold frame.

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DIY cold frame

Cold frames come in many shapes and sizes.  The frame you’ll see here is the style we built ourselves to fit the existing raised beds in our kitchen garden.  

The good news is that you can adjust this design to fit the raised beds in your own garden!  Below you’ll find instructions, plus recommended tools and materials for building a DIY cold frame. 

Want to see this cold frame in action and watch us build one?  Check out the video below!  Can’t see the video?  Click here to watch.

More cold frame options

• How to Make a Straw Bale Cold Frame
• How to Build a Cold Frame Out of Pallets
• Portable Zipper Cold Frame
• Premium Polycarbonate Cold Frame

How to use a cold frame for winter harvest

A cold frame allows you to extend your growing season by protecting tender veggies from freezing temps.  In my zone 7A garden, I grow greens such as lettuce, kale, chard, and spinach into the winter months by covering them with a cold frame.

A cold frame won’t help your seeds germinate in the cold, but it will protect already growing plants from hard frost. I use cold frames to protect my existing veggies sown in the spring, summer, or fall in order to continue harvesting into the winter.

In fact, I love to grow fall crops of greens, knowing I can protect them well into the winter with a sturdy DIY cold frame.

Without protection from a cold frame, lettuce will succumb to frost.  Kale, chard, and spinach will not die in freezing temperatures, but they will halt production and their leaves will sustain frost damage.

However, when protected with a cold frame, these veggies will remain fresh and ready for harvest, without damaged or dead leaves.

>>Get more details about fall veggies: 16 Best Veggies for Your Fall Garden.

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How to use a cold frame in the spring

In the spring, a DIY cold frame can allow you to plant a bit earlier than usual.  If you’re worried about late spring frost, a cold frame can provide that extra protection to keep your baby plants safe.

You’ll also notice that last year’s greens which were protected under a cold frame will kick back into production even earlier in the spring, or even in late winter.  This adds up to an earlier harvest from last year’s plantings!

Keep in mind that greens planted last year will not last long into the current growing season.  As soon as temperatures warm up, they’ll bolt and go to seed.  

However, I love to plan for an early spring harvest of last year’s cold-frame protected greens, combined with newly spring-sown greens that will start producing right about when last year’s greens are petering out.

Both plantings fill a gap that the other cannot, which leads to an extended harvest.

Get more details about spring veggies: 12 Best Veggies for Your Spring Garden.

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How to store a DIY cold frame

One potential downside to this sturdy DIY cold frame is storage.  The cold frame does not collapse, so you’ll need adequate space for storing it during the warmer months.

The good news is that it’s easy to detach and remove from your existing garden bed.  Simply remove the screws and mending plates at each corner and lift off.  Then store, away from the elements, until later in the year.

How to build a cold frame

These instructions are for a cold frame to fit a 2×10 raised garden bed.  However, the design can be adjusted to match the dimensions of any garden bed, so feel free to modify according to your needs.

Tools

• Power drill
• T-square
• Measuring tape
• Skill saw
• Pencil
• Hammer
• Wire snips

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Materials

• (2) 2×12 – 10′ or 12′ untreated
• (1) 2×8 – 10′ untreated
• (2) 2×4 – 12′ untreated
• (1) 1×3 – can be scrap, untreated
• Clear polycarbonate: 26″x12′
• 3″ deck screws
• Small wood screws
• #10 5/8″ hex head self-drilling screws
• (8) 6″ zinc plated mending plates
• (3) 3.5″ hinges
• (4) galvanized angles
• Optional: sturdy chain
• Optional: latch (4 5/8″ double bolt snap + eye screw)
• Optional: hook & eye

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Instructions

These instructions will make much more sense when paired with a visual picture in our DIY cold frame demonstration video.

1. Assemble the base of the cold frame to match the dimensions of your existing raised bed.  My beds are 2×10, so we cut our cold frame base to match that size.
   1. Cut one 2×12 to match the length of your existing bed.  For us, that was 10′.  This is the back of the cold frame.
   2. Cut the 2×8 to match this same length.  10′ for us.  This is the front of the cold frame.
   3. Cut one 2×12 to match the short sides (two) of your existing bed.  These two short sides should fit inside the two longer lengths you have already cut, to match the dimensions of your existing bed.  For our 2×10 beds, our short sides are just under 2 feet.
   4. On a level surface, arrange the four pieces to form the base of the cold frame, but do not attach yet.  You will likely need a helper for this step.
   5. With a pencil, mark each short side at the top where they meet the longer sides. 
   6. Use these two marks to draw a straight line, and then cut on that line to create sloping sides. 
   7. Now you are ready to attach the four sides of your cold frame base, using two 3″ deck screws at each corner. 
2. Assemble the lid of the cold frame to match the base of the frame you have just assembled.  Note that the lid should have a slight overhang for ease of operation.  
   1. Cut the 2x4s to form the long sides of the lid, which should match the base of the frame exactly.
   2. Cut the 2×4’s to form the short sides of the lid, which should be a bit longer than the short sides of the base.  This will create a slight overhang at the front of the cold frame lid, which will assist in opening and closing.  
   3. Use a hammer to bend two 6″ mending plates, ever so slightly.  
   4. Use small wood screws to attach these two plates and connect the lid, one plate in each upper corner.
   5. Use small wood screws to attach two more 6″ plates to the lid, one in each lower corner.
   6. Cut the 1×3 to serve as a cross piece running from the top edge of the frame to the lower edge of the frame.  
   7. Attach this cross piece in the center of the lid, using two small wood screws, one at each end.
3. Attach the lid to the base.
   1. At the top rear of the cold frame, measure in about 12″ from each corner.  Use small wood screws to add one hinge at each of these spots.  
   2. Center the third hinge between these two hinges, attaching with small wood screws.
4. Add clear polycarbonate to the lid.
   1. Position polycarbonate on top of the cold frame lid, lining it up on one side and attaching at the upper corner with a hex head screw.
   2. Check again to make sure the polycarbonate is lined up on three sides, and attach at the lower corner with a head head screw.
   3. Keeping the polycarbonate lined up with the lid frame, continue attaching it to the lid frame using hex head screws approximately every 6-8 inches.
   4. When the polycarbonate is attached on three sides, use the wire snips to trim off the excess.
   5. Attach the fourth side of the polycarbonate to the lid frame with hex head screws.
   6. Attach the polycarbonate to the cross piece with hex head screws.
5. Optional: add a chain at each end of the cold frame.
   1. Our kitchen garden receives high winds and therefore, our cold frame lids require extra measures to remain securely closed during gusty weather.
   2. See the video to note how we used a sturdy chain to attach the lid to the base at each end of our cold frame.
6. Optional: add a latch at the front of the cold frame.
   1. We used a 4 5/8″ double bolt snap and two eye screws.
7. Position the cold frame on top of the existing garden bed and secure in place.
   1. Inside the cold frame, attach one 6″ mending plate near each corner to secure the frame to the garden bed.
   2. Use small wood screws to secure the mending plates.
   3. Note that these mending plates are easily removed in the spring, when it’s time to put away the cold frames.

Have you tried extending your harvest with a cold frame?  What would you grow under a cold frame?

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