I bought this planter box at a yard sale for $5. I think it may not be used outside as the heat or moisture may have caused the corners to warp and come apart.

Image of planter with separated joint

Two corner joints are really bad (see photos) the other two not so much. If this can be fixed, I could do it or find a local woodworker to fix it. What does the fix entail if it can be fixed.

3 Answers 3


I would say that it is more likely that this joint failed due to the moisture from watering the dirt rather than being outside. Simply re-gluing it and keeping it inside will not be enough to fix it.

I can foresee a few options

  • Glue up the joint again as it was and this time line the planter with plastic so that the moist dirt does not come in direct contact with the planter. However for the health of the plants, you will almost certainly need drainage holes in the plastic, and it may be difficult (but not impossible) keep the wood dry around the drainage holes. Still, moisture in the center of the bottom of the planter will not affect the joints as much as before.


  • Use a nail gun to secure the joint. Nails are much more resilient against wood-movement. If you do it properly and place two nails the same distance from the top and bottom of the planter, it will still look nice.
  • The reason why I think moisture or heat may have caused the failure is that I don't remember the opening of the joints being as wide as they are now. Also, this does have a metal liner and there isn't any evidence of dirt around the inside of the box. I like your two solutions. Do I first try to clamp the joints. The wood seems to be very stiff and does not seem to move/bend at all.
    – user435
    Apr 19, 2015 at 21:16
  • @user435 then there is a moisture problem, let it dry out completely or put it in a 100% humidity chamber and see it bend straight. Apr 19, 2015 at 21:38
  • Regarding the drainage holes, you can use pvc tubing to create a safe channel through the wood out the bottom of the planter. Cut a hole through your liner and the wood, and seal the connection with caulk or some other sealant. You'll want to use a fitting that will keep the pvc from falling out the bottom. Or you could just epoxy it to the wood.
    – Daniel B.
    Apr 20, 2015 at 14:41

Easiest would be splicing in a little triangle reinforcement.

As described in this article.

You will need to clamp the corner closed when you make the cut in them and glue it up again. Here is the required cut in the box depicted with a half finished computer case:

enter image description here
(image source)

  • 2
    FYI the little triangle is commonly called a spline.
    – rob
    Apr 19, 2015 at 21:33

You can use some metal angle brackets to reinforce the inside of the box.

As to the warping, boards usually cup like that when one side dries faster than the other. Having a metal container that lines the inside will reduce the rate that the inside face drys, which will cause that cupping. You might be able to reduce that effect by sealing the outside well with some clear coat deck sealant.

You could possibly reverse the cupping by wetting the wood and placing it in the sun so that the inside gets the light, and covering the outside with a plastic film (duplicate the initial effects in reverse).

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