DIY Cold Frame Garden Beds (Shou Sugi Ban Finish)

I’m so excited to show you how we built our new DIY cold frame garden beds with a super cool shou sugi ban (wood burned) finish.

The Benefits of Cold Frame Garden Beds

Cold frame garden beds help extend the growing season.  I have wanted to try gardening for years but was worried that my poor little plants would get hit by a sudden cold snap in May and perish.  Our growing season is so short here on Lake Superior!  UPDATE: A few years later, I have LOVED that these cold frames protect my seedlings from frost and extend my growing season deep into the fall – these cold frames have been so perfect for my colder climate!

Below is a list of everything we used to make these DIY cold frame garden beds.  Hubby found a small, local saw mill through a friend and we bought 2″ x 6″ x 8′ rough hewn cedar lumber for our cold frames, but you can use different lumber.  The best wood for cold frames is something that is rot resistant.

Supplies for DIY Cold Frame Garden Beds:

• 2″ x 6″ x 8′ rough hewn cedar boards (about 9 per box)
• 4’x8′ Lexan sheets (x 3)
• 3.5″ deck screws
• Drill
• Straight edge
• Jigsaw
• Miter saw (you can also use a chop saw or the jigsaw again)
• Table saw
• Shed pulls (x6)
• 6″ T-hinges (x6)
• 1″ screws and washers (plated or stainless)
• Medium duty chain

Shou Sugi Ban Supplies:

• Propane torch (I bought this exact one)
• Propane tank
• Tung oil and lint-free rags
• Fire proof gloves (like those used for welding)
• Safety boots

DIY Cold Frame for Raised Beds Tutorial:

This DIY cold frame for raised beds tutorial is broken down into three sections:

1. How to build a cold frame garden box
2. How to create a shou sugi ban finish on garden boxes
3. How to build a cold frame lid

How to Build a Cold Frame Garden Box:

1. Cut the boards for the four sides, using a sliding miter saw.  To make it simple, our boxes are 4’x8′.
2. Cut vertical support pieces to length from the same lumber (we ran them through a table saw to cut them to approx 2″x 2″).
3. Position the support pieces (in the center of the 8′ sides and inside the corners) and pre-drill holes.
4. Using deck screws, assemble the longer front and back first, by laying the boards on the ground and screwing on the vertical supports to hold the boards together.
5. Once the front and back are assembled, add the side boards one by one by standing up a board and screwing the corner support from the inside to attach it.
6. To create the slanted shape, take a board that was cut to length for the sides and divide it in half with a straight edge pencil line to make two triangles.
7. Using a jigsaw, cut along the line.
8. Then attach it to the top of the garden bed, on either side.

Here’s a closer look at the construction of these DIY cold frame garden beds:

You can skip the slanted design for a simple garden bed without the lid.  Or add more wood boards to make it taller.  Below is the finished garden box for the DIY cold frames.  Next I’ll show you how to char the wood and make cold frame garden box lids.

Shou Sugi Ban Finish for Garden Beds:

I decided to use my favorite technique: shou sugi ban, for finishing the wood.  Cedar is rot resistant naturally, but charring it adds even more weatherproofing to the wood.  Plus, because the new house exterior is a dark grey/brown, the charred wood garden boxes blend in more.  You can get better coverage if you char the wood before it’s assembled (otherwise it’s difficult to char between the boards) but this way is EASIER – you don’t need to handle the charred boards or prop them up anywhere.  But it always looks better to char wood before it’s made into something.

For this wood burned project, I upgraded my tools and bought a 500,000 BTU propane torch. It’s AWESOME!  You can char much more wood at a time than the smaller handheld propane torch I was using.  This is far more effective for a larger project like this.  (And way more fun).

I also wore my fire gear –  but you don’t need it, lol!  I originally just wanted to see if my bunker gear still fits.  My municipality finally sprang for my own custom turn out gear, but that was back in the winter.  Once I had it on, I thought I should wear it for awhile because it’s so heavy and we don’t have many fire calls, so I’m really not used to wearing it.  You’d be fine in some coveralls, gloves and work boots.  It DOES get hot (it’s fire!), so please DIY safely.

How to Use Shou Sugi Ban for Garden Boxes:

1. First, bring the garden boxes to an area that is NOT flammable (stay away from grass) – gravel or concrete is safer.
2. Soak the nearby area with a hose, so if an ember flies the area surrounding it is wet and less likely to catch fire.
3. Keep a hose nearby just in case (treat it with the same safety you would a bonfire!)
   
4. Put on your PPE (eye protection, BBQ or welding gloves, safety boots, coveralls, etc…)
5. Set up the propane torch and start charring!
6. Work in sections and char the wood darker than you’d like the completed finish, as it will lighten up.
7. Use sweeping motions to char the wood and work around the garden box, being careful not to char the hose or get too close to the propane tank with the flame.
8. Hose off the wood when you’re done with charring.
9. Once the wood has dried, you can use a stiff wire brush to release any debris (optional).
10. Seal with tung oil (optional – details in next section).

Shou Sugi Ban Tips:

Once you’ve charred an area, the flame will disappear.  It won’t light the wood on fire!  But if an area DOES stay lit with a little flame, just give it a tiny spray of water.  See more of my shou sugi ban experiments here and here.  Traditionally – and for indoor applications – I use a stiff plastic brush to remove the soot off, and char some more, and then brush again, and finally seal.  That method, although labor intensive, creates a dark finish that won’t shed charred wood.  But this is a garden bed!  It won’t be touched as much and it will live outside where it will see rain and snow.  So once I was done charring the whole bed, I soaked it with a garden hose to remove an loose bits.  No brushing!  Then the next day I charred any areas that still looked light.  But I skipped the brushing, just because I was lazy and this was a larger project.

Shou Sugi Ban Garden Boxes

When the cedar wood for the cold frames was charred, and hosed off, the shou sugi ban garden boxes looked like this:

Charring Instead of Sanding Rough Hewn Cedar:

The cool thing about the wood burning is that it burned off the roughness.  We would have had to pay extra for planed wood but because it’s just for garden beds, we decided to buy the cheapest and rough hewn was really affordable.  It had these rough little bits though, which I didn’t like, but all of that got totally burned off and the charring created a smooth, sliver-free finish which is an awesome benefit of this wood burning technique!  I would rather burn than sand, that’s for sure!

Do You Have to Seal Wood After Shou Sugi Ban?

I wasn’t going to seal my shou sugi ban DIY cold frame garden beds, but people asked me if it was going to rub soot off if you touched it.  After being in the rain and sun for weeks, there was very little soot, even if I rubbed a shirt against the edge.  But I decided to seal the shou sugi ban anyway, so I could test it out for people who really get in there to garden.  I used an old t-shirt and rubbed tung oil over the outside sides and top edge (not the inside – no need).  I used another clean rag to wipe off an excess.  One coat and the tung oil sealed the charred wood beautifully – no transfer.  Tung oil is an all natural, appropriate sealant for a DIY garden bed.  Linseed oil is another option, but it cures much more slowly and boiled linseed, although a quicker curing formula, contains a small amount of lead.

How to Position DIY Cold Frame Garden Beds:

After soaking them with the hose, we left the DIY cold frame garden beds on the driveway overnight just in case there were an embers (again, an abundance of caution).  In the meantime we marked where we wanted them to be and then dug up the sod.  I made sure I left enough room between them to fit my lawnmower and enough space behind them (and my raspberry bushes) to pick berries and weed back there.  I waffled about laying down landscape cloth and at first I wasn’t going to but underneath the sod is rock hard clay anyway so it’s nothing my plants could use.  Se we laid down the landscape cloth to prevent grass and weeds from poking through.

Then I shovelled a 3/4 tonne truckload of topsoil.  Why does it seem like for every outdoor project, I am stuck shovelling something out of the back of my truck???

Unfortunately, even if we had wanted to, we couldn’t leave our garden beds without lids lol.  Look at that guilty face of Szuka’s.  And Hynda was right in there too.

How to Make a Cold Frame Garden Bed Lid:

For the lids, we knew they’d be heavy so we made two individual lids to make it easier to lift – and also for less weight for the hinges, which automatically raise a lid when the garden bed gets too hot.  We created the frames using more of the cedar we bought, ripped into 2″ x 2″ boards and screwed together with deck screws.  Then I charred them and sealed them, just like the garden boxes.

What Kind of Plastic is Used for Cold Frames?

We chose Lexan for the cold frame lids because it’s safe to use in extreme cold exterior applications (it won’t get brittle or discolor).  And if a snow heap falls off the roof, we won’t get broken glass everywhere – but you can also use old windows, etc., but just be mindful of where you place it to avoid anything falling over and shattering the glass.  We found that Lexan was very easy to work with: we cut the Lexan with a jigsaw to fit over the two lid frames we built for each box.

We screwed the Lexan on top, using 1″ screws and washers.

Then it was time to attach the hardware!  We used these hinges to affix each lid to the garden box:

Finally, we added shed pulls for handles to each lid and some chain attached with screws and washers, so when the lids are open all the way they’re supported.

That way I can open them all up and water at once – or if it’s super hot, let the garden beds be totally open.  Here’s a look at our finished DIY cold frame garden boxes:

The Finished DIY Cold Frame Garden Beds:

Here’s a peek at my little garden growing!  And check out this post to see the cold frames with full grown plants.

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