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So I attempted to make a simple raised garden bed out of box store 2x12s and 2x4s. I cut the pieces to length and square (using a circular saw) and went to attach the pieces with butt joints secured with decking screws. However, when I went to secure the final side, the whole thing was warped and would not sit on the ground without racking up and down. Also the ends would not line up flush or square.

I am thinking about redoing this because it bugs me. Was this an error on my part or is this due to warping of the boards I bought? How would I prevent this warping from occurring the next time I make one as I need to make two more? Any advice would be much appreciated! Thanks!

Here are the pictures: https://imgur.com/a/MEmUKku

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    Lots of good info below, but what did you use to establish a square line to cut? Your cuts look out of square to me. (You can test this by checking square from one long edge, then flipping over and checking from the other long edge.) Advice below suggested using pressure treated lumber... I would never consider this if I was growing food, and I wouldn't even be enthused if it was flowers. Let regular lumber rot and replace it in a bit. (A perimeter of gravel for drainage will help a lot.) – Aloysius Defenestrate Apr 16 at 15:12
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    I am brand new to gardening and just wanted to get a box up quickly. I didn't use pressure treated lumber because I want to grow vegetables and from what I read it was ill advised to use pressure treated lumber (although I have seen conflicting things stating it's safe nowadays). I was honestly in a hurry to get it done. I used a speed square as a guide against my circular saw, but I honestly did not take the time to make sure everything was correct. My thinking was "its a box, how hard can it be to make". Clearly, I was mistaken lol. – agentbanks217 Apr 16 at 15:22
  • "safe nowadays" is what they said about the last generation of PT when they were trying to sell it. Call me a cynic, but I fully expect this generation of PT to be found lacking on the safety front. For what it's worth, I like to draw a line and cut to it, rather than have to manage a square and a saw at the same time. Everybody's different, though, and there are numerous ways to get things done safely. – Aloysius Defenestrate Apr 16 at 15:28
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How would I prevent this warping from occurring?

You wouldn't. Wood is a natural product and warping is what it naturally does. However, you can mitigate the effects. You can buy engineered wood products that won't warp, but I doubt that the cost would be acceptable for a project like this, and I don't know if engineered wood is available in pressure-treated for ground contact. (If it is, the price is, I'm sure, even higher.)

Wood Quality:

Did you confirm, before purchasing, that you were choosing the flattest, straightest, least warped boards in the pile at the big box? I've been known to set aside a dozen boards just to find one that I felt was true enough for my purposes. My wife and I can plan on an hour, minimum, at the lumber stack if we're picking up a large pile of wood for a project. (I've been known to put >50% into the "nope" pile. When it came to choosing the very visible decking for our recent deck build, it was probably >70% into the "nope" pile.) If the wood will be exposed, don't forget to check for knots, splits, checks and discoloration on the surface(s) that will be exposed. If the boards were warped, to begin with, it takes a lot more effort to ensure that your project will come out squareish.

Looking at your pictures, it looks like you've used untreated wood. That will not last very long in contact with dirt. It will begin to rot and fall apart almost immediately. You'll probably get 2 years where the top looks decent, but the part in contact with the ground will be rotting away. By year 3, you'll probably have visible rot visible near the top of the box. You'll want to purchase pressure-treated lumber that is rated for ground contact. At my preferred big box, they have "ground contact" and "not ground contact" rated PT. I'm not 100% certain the differences, but the cost factor is small, so it was worth it to me (especially for posts that support my deck, YMMV).

Dealing with crown:

To accommodate warped wood (all wood is going to have some warp to it unless you're buying kiln- or air-dried lumber from a quality lumber yard, i.e. not a big box, and even then, it can move on you when you cut it) you'll have to work with the wood instead of just assuming that everything's flat and square like a piece of steel would be.

If there is a bow in you 2x12 along its length, is it a slow, steady even bow? If so, you can probably find 2 reasonably matching sections of bowing.

  • Cut your long lengths from these matching sections.
  • Cut them a couple of inches longer than your then your finished length. (See the first point in the "Work with it" section. If you're going to use that method, add some to that measurement.)
  • Stand them next to each other on their 2x edge on a level floor (like the garage).
    • You'll want them to be crown up - they should be stable on the floor that way.
    • If you put them crown down, they'll want to rock which will make the next step more difficult since they'll be moving.
  • From there, mark a vertical line using a square to the floor.
    • When you lay them down to recut them, you'll see that these new lines are not square to the wood, but they'll be vertical when these side rails are stood back up.
  • Duplicate this process for the 2 short ends.

You'll now have 4 boards that have a vertical crown when stood on edge in the orientation you'll be assembling them, but most importantly they'll have edges that will match flat so they can be screwed together and meet up neatly. If this vertical crowning is unacceptable, you can use a straight-edge to mark a line that will cut off the crown. Cut this with your circular saw. You'll end up with a piece that's flat on the top and curved on the bottom - since the bottom will be buried in the dirt, it won't matter. In theory, the crown you cut off the top should, more-or-less, fit into the arch left on the bottom - you could glue and screw it in if the crown is significant.

Dealing with a twist:

If the boards have twist across their face (the 12" dimension) you have options. If you have a surface planer, you can plane the warp out, but then you end up with thinner boards that may not be suitable for the purpose. If the warp isn't too severe, you can simply work with it and forcibly pull the warp out as you assemble, or you can cut to accommodate the warp.

Force it:

To pull the warp out:

  • If it's not too severe, you may be able to simply push the board flush when you're screwing it in place, then add an extra screw or two to hold it there. Be warned, though, that the wood will want to move back, and you may end up with it pulling past the screw heads.
  • If the warp is more severe, you may be able to use clamps to flatten the warp then use lag screws with washers (into predrilled holes) to hold the surface to the edge grain of the adjoining board. Again, the wood will want to move back and you may end up with splits as it does so.

Work with it:

To cut to accommodate the warp, scribe the joints:

  • In this process, you'll be cutting roughly 1.5" off of each end of your long boards. Make sure you account for this when cutting the long boards by cutting them 3" longer than the desired finished length.
  • Align the board to overlap (that would be the board we see end grain on in your picture #2, on the left) against the face of the board it's to overlap (the surface grain board in pic #2, on the right).
  • Square the boards up the very best you can (ensuring that the joint remains square).
  • Use a pencil to draw a line along the end-grain board onto the face-grain board.
  • Use a jig-saw to cut the face-grain board along this line.
  • When you bring them back together in their original alignment, they should mate up pretty accurately.
    • You can tweak your jigsaw cut as necessary to meet your standards of tidiness. (Adjust the cut with the jig-saw, a rasp or file, or sandpaper as you feel necessary.)
    • Remember that some of the joint (looks like) it will be buried, so that part probably doesn't have to be quite so neat (i.e. save some time here).
  • Your corner on the face-grain board will no longer be perfectly vertical, but it will be a reasonably tight joint to the board around the corner from it and, unless there's a severe twist, it won't be obvious because you've got a tight joint. Additionally, some of this not-square-joint could be covered in dirt if you plan properly. (I keep mentioning that because it looks like you're building this into a slope and I'd imagine you'll back-fill to match the slope.)

Fasteners:

I'd think that your deck screws will be sufficient for quite a number of years.

  • Be sure you're using ones that specifically indicate that they're suitable for use in treated lumber (most decks are made of treated lumber, so that should be most deck screws).
  • For any that will be directly exposed to dirt, you might want to consider the extra expense of stainless steel screws. SS screws are quite a bit more pricey, though, so you'll have to decide on your price vs life-span tolerance.
  • You may want to increase the number of screws you're using. I'd guess you used 3 on a 12" run. You may want to up that to 4 screws.
  • Consider pre-drilling pilot holes, even though many deck screws have drill-type tips.
    • Using a small pilot hole bit will help reduce splitting when putting them in near the edge on either long- or edge-grain. Especially if you need to put more than one screw into a single growth ring.
    • A small pilot hole bit should allow for a straighter hole for better alignment into the long length of the adjoining board.

Fixing This Box:

If you want to fix this box without cutting the ends to make it smaller, you could cut the warp off.

  • Take the box to a hard, level surface.
  • Remove the 2x4 top cap.
  • Insert some shims under the high points to hold it steady (or enlist a helper - put the kids to work!).
  • Use a level to find the lowest top corner.
  • Draw a level line around the box from the lowest corner.
  • Mark the 4 corners (near the bottom of the corner) to ensure you reassemble in the correct order.
  • Disassemble the box.
  • Cut the boards down at this new level line.
  • Reassemble the box.
  • For the corners that are slightly out of alignment (pic #2), I'd simply pull them into alignment on assembly and add an extra screw.
  • Reattach the top cap (some fettling may be required to make it fit properly now).

The bottom of the box won't be square, but you can bury the low points a bit to hide the sins and call it good.

You may end up with some splits and checks, but since you're intentionally using non-PT lumber for your veggies, you'll be replacing the boxes every few years anyway, so it shouldn't be too big an issue.

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  • Thanks for the detailed response! Admittedly, I was in a hurry to complete this and did not take the time to pick the best lumber out at Lowes. I used non-treated wood, knowing it would degrade and need to be replaced, because I did not want to use pressure treated wood for a vegetable garden and cedar boards were too expensive. Would there be any way to correct this current bed to make it less warped or would I have to rebuild it? I will definitely try crowing the boards on my next bed and leaving some overhang and trimming the excess off, and hopefully that will help. – agentbanks217 Apr 16 at 15:57
  • Re: PT lumber - go with what works for your situation. You didn't specify veggies, so I didn't really think about that. You could rebuild this one by following the suggestions I made and just making the box smaller as you recut the ends. For other thoughts, see the additional notes in my answer. – FreeMan Apr 17 at 12:51
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In a living tree, wood pulls water out of the ground like a sponge and moves it up to the leaves. That function still contines after the tree is dead especially if it's been cut recently, and pine is particularly prone to this compared to other timbers. Timber grows/shrinks/twists/etc as water is soaked up and also as it dries out.

Exterior grade paint/varnish/oils/etc will help, but that might not be enough for the amount of moisture you have and may not be the look you're going for?

Some timbers that are more stable than others, but that gets expensive and for such extreme moisture the problem might not ever go away completely. Also it's a good idea to expose timber to the level of moisture it will experience for the final installation before cutting it/etc. But for outdoors in the element you're going to deal with constant moisture changes throughout the day and seasons.

I would bolt the timber some kind of rigid frame made of heavy duty steel brackets which could be hidden underground. You'll also need to disassemble the box, clamp it to the frame and re-do the cuts since they're not 90 degrees anymore.

Also wherever possible design your box in such a way that it still looks good even with movement. For example instead of having two pieces of timber flush you can add a finger's width of overhang. If the size of that overhang changes slightly between autumn and spring... it'll still look fine.

The screws you used don't look very strong either, stronger fasteners and glue will help. Some glues dry hard/rigid which will prevent movement but may crack if stressed too much. Other glues are soft and flexible and allow a bit of movement without losing their strength. Which is better depends on how much movement there's going to be.

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  • Thanks for the detailed response! I was in a hurry when I did this and it clearly shows. I think I may redo it now. I used 3" decking screws with an impact driver to make them tight. Could that be cause of the warping as well, from driving them in too deep/tight? – agentbanks217 Apr 16 at 15:27

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