Wooden planters always rot, and plastic planters are degraded by the sun, so what should large planters be made of? A wooden shell, with plastic boxes to hold the soil. In that way, the wood doesn't rot, as it isn't in contact with the soil. The plastic doesn't deteriorate, because it is completely hidden from the sun.
You look my Garden Furniture designs on GitLab. (Scroll down till you see the Planter image).
The planter's "skin" is made from 3 rings of decking boards. The sit on battens which are attached to the bottom ring. The other two rings just sit on top of the bottom ring.
Construction is quite straight forward. I like to use decking boards, as they are cheap, sturdy, and the ridges give an extra bit of interest.
First, buy 3 plastic boxes about 30cm long. Drill plenty of drainage holes in the bottoms. If the boxes are deeper than you require, fill the bottom with broken expanded polystyrene packaging. Then add the compost, and plant up as required. Don't plant right up to the edge, because the trim will hides the boxes from the harmful UV rays will get in the way.
Here's the cut list :
- A) 6 of BOX_LENGTH * 3 + WOOD_THICKNESS * 2 + 2cm spacing.
- B) 6 of BOX_WIDTH + 0.5cm spacing.
- C) 2 of BOX_LENGTH * 3 + 2cm spacing (cut at a 45° angle at both ends)
- D) 2 of BOX_WIDTH + 0.5cm spacing (cut at a 45° angle at both ends)
- E) 2 of BOX_WIDTH
The boxes sit on top of these, and are not visible in the final product. I use deck boards cut in half lengthways.
- F) 6 of BOX_WIDTH + 0.5cm spacing
I often have offcuts lying around that fit the bill! Fairly chunky, buy doesn't have to be a thick as a fence post.
- G) 4 of 20cm or so, the choice is yours!
- H) 8 of 10cm or so.
Create the three "rings". Each ring consists of 2 x A and 2 x B attached with screws (I find decking screws work well, as they don't rust).
Screw the corner pieces (H) to 2 of the rings (the top ring doesn't need them).
The three rings should now fit together.
Cut C and D, so that they form the trim, which fits INSIDE the top ring.
On a flat surface, arrange the trim, the boxes and the rings all upside down, so that the bottom ring in top-most, and the trim is on the floor.
Cut the battens F. Place 2 battens on the bottom of the each box. Screw the battens to the bottom ring. (By arranging everything upside down, the battens will be at the correct height without needing to measure).
Cut the legs (G), and screw to the bottom ring. The legs are the most likely to rot, as they will be in contact with the ground, and may get waterlogged. That's ok though, because it's dead easy to replace the small stumpy legs every five years or so!
I like to use a good quality thick "fence paint" for the rings, and a water based exterior matt finish paint for the trim.
When re-painting, the fence paint can be re-applied very easily (remove the trim and the boxes!).
The trim will need to be sanded before being repainted, but assuming you have a sander, this is easy,and doesn't take long, because all the pieces just fall apart (they aren't screwed in place). So there's no concave parts where a sander cannot reach ;-)
My First Version is now nearly 8 years old. The legs had began to rot, but the rest is perfectly fine. I expect them to last for another 8 years at least. I must re-paint them more often though, because 8 years is too long.
Initially I used garden soil (I now use compost). Due to the weight of the soil, the plastic handles broke when lifted, but since I've been using compost, the plastic has survived just fine. No brittleness, as the plastic is never in view of the harmful UV rays from the sun.