So, I did, and I don't think it turned out too badly.
The plastic is all re-purposed and the only other materials I needed were some small screws, caulk (both of which I had on hand) and paint (which was on sale).
Step 1: Materials and Tools
Large plastic jug
Plastic bottles or cups if that's what you have available
Paint for plastic
Heat gun or hair dryer
Drill and 1/2" drill bit
Clamps Blocks of wood
Scraps of wood for wedges
Step 2: Remove the Jug Handle and Cut the Holes
Remove the handle by cutting one end of the pin that holds it in. Use the handles for some other project. I made a handbag with mine.
Use a heat gun or hair dryer to soften the labels to remove them.
Turn the jug upside down and cut out a rectangle, leaving an edge all around. Mine had a raised edge, so I just followed the crease. (Picture #2)
Mark off where you want your holes placed on the jug, measured according to the size plastic bottle/cup you have. I made sure mine were staggered all around, so all four sides are different. (Pictures #3,4,5)
Cut the holes out on the sides and top only, using a SoniCrafter or whatever you have that will cut this tough plastic. Then cut off the top 2/3 , leaving the bottom 1/3 to attach your bottle/cup to. (Picture #6)
At this point, I scored along the bottom, so the flap could be bent inward.
Step 3: Cutting the "pots"
Use the miter saw to cut off the top of the bottle. (If you are using plastic cups, you can skip this step). (Picture #2)
Clamp boards to the miter saw to make a jig to cut the bottles in half top to bottom. (Picture #3)
This is what you'll end up with. (Picture #4)
Finish cutting the rest of the way with a kitchen shears.
Step 4: Adding the "pots"
Use a file/rasp to take off the splinters left behind from cutting. They don't have to be totally smooth. (Picture #3)
Set your half bottles/cups in the holes of the planter. The top of the "pot" should be just a little above the top of the hole, just so it doesn't slip inside. Cut of any excess bottle/cup. (Pictures #4)
Drill a hole a little smaller than your screw through each bottle/cup half bottom and the flap on each hole. Screw each cup to each flap. (Picture #5)
Step 5: Caulking the "pots"
Caulk around the outside edges of each "pot", sides and bottom. Caulk on the sides of each "pot" on the inside.
This is what you'll have, minus the peanut butter which I used to get most of the residue from the labels off. (Picture #3)
After this has dried, you'll probably need to check it over and recaulk any areas you missed.
Let cure for time advised and drill drainage holes in the bottom of the planter. (Pictures #4&5)
Sand it just to roughen it up a bit and wipe it down. You are now ready to paint.
Step 6: Painting
If you're not fussy, you could use it like this, but I wanted a more finished look.
Paint with a spray paint made for plastic. I used Rustoleum Universal in a brown hammered finish. I thought this would look the most planter like.
Step 7: Finished and Planted
And here it is all planted. I'm sure it will look much nicer once the plants are established. (Picture #2)
(Picture#3) A round Strawberry jar painted with strawberries.