Here's my entry to the 2020 Cardboard Speed Challenge! I wanted to create something that's fairly easy to make, doesn't require any fancy tools, and is something that people can use everyday.

This design perfectly fits a small mason jar to put your plants in, but you can experiment with other geometric shapes and sizes to make your own custom planters.

Step 1: Gather Materials & Tools

Corrugated Cardboard (Size must be at least 13" x 13")
Carpenter's Glue
Tape
Paper
Pencil
Ruler
Box-Cutter
Scissors
Computer or Tablet

Note: You can also use Single-Ply cardboard, but it might not be as rigid. You can also opt for a Hot-Glue Gun, but I didn't have one.

Step 2: Create Stencil

I found the easiest way to get the dimensions of the shapes correct and consistent was to create a stencil by tracing the shapes on a computer or tablet. You could also print these out, but tracing them is really fast.

Start with the hexagon. It should be around 3" from a flat side across to another flat side. Just trace the corners for now, and go in after with a ruler to get perfectly straight lines.

Next, trace a pentagon off of the side of the hexagon. You will need to adjust the size of the pentagon so that its side is roughly equal to the side of the hexagon (as seen in image 3 above).

Now you are ready to add the nice straight lines between your corners.

Finally, cut the outside lines with either your scissors or a box-cutter. Keep the shapes connected for now.

Step 3: Draw the Cut Lines

Place the hexagon as close to the centre of the piece of cardboard as possible. The direction of where your first pentagon goes doesn't matter too much, but I would recommend going along the corrugated grain of the cardboard.

Use the same technique as before to trace the corners, then go in after with a ruler to get straight lines.

Once the first pentagon is marked, you can rotate the stencil 60 degrees. The hexagon shape of the stencil should match the hexagon on the cardboard - now you're ready to trace your second pentagon! Continue this pattern for all 6 pentagons.

You should now see a flower shape.

Cut the stencil so that the pentagon and hexagon are separated.

Using the new pentagon stencil, create another layer of pentagons on the cardboard that branch out to the right. You can also do the left - just make sure it's consistent all the way around.

You now have a snowflake!

We're not quite done yet though, because we need to create some tabs so this planter glues together strongly. I draw these by hand, since they won't be seen - once they are cut, they are only going to be the back sheet of cardboard with the corrugated material and front layer cut away - just follow the shapes in image 8 and trust me on this one!

Finally, I would recommend partially erasing all of the lines between the hexagons and pentagons, so that you don't accidentally cut them apart.

Step 4: Cut!

Let the games begin! ...Safely of course, box-cutters are really sharp and should be handled with care. Also, make sure you're cutting on a stable surface that you don't mind having knife marks on (I used the top of a plastic storage container).

Start by doing a very light incision with the box-cutter along the perimeter of the snowflake shape - don't worry about the tabs here. Your goal with this first pass is to just precisely follow the lines of all those pentagons. The first picture above shows how lightly I cut.

Okay, now you can get a little destructive! Cut around the tabs (don't cut them off!) and feel free to go all the way through the cardboard. I still recommend doing multiple thin cuts.

You can also cut all the way through the edges that don't have tabs. Do you feel how the first light cut guides your blade? PRO TIP: Cut at a bit of an inward-angle (as shown in the third image) to get cleaner connections when this all folds together.

Once you've cut around the beautiful polygons and ugly tabs, you can start removing the excess cardboard. You will probably need to keep cutting parts you've missed. Check the back of the cardboard to see where you need to cut more.

You should be left with just the snowflake shape and the tabs.

Now is time to cut away the top layers of the tabs. You probably need to go over them again with another couple light cuts, but do not cut all the way through. You can fold them and peel away the top layer and corrugated parts.

Continue cutting away all the tabs, then go over your previous cuts to make them as neat and straight as possible, removing dangling bits of paper that didn't get totally removed.

Step 5: Fold!

Now you want to mark the fold lines on the back side of the cardboard. I just flipped the cardboard around, checking that the back-lines matched the front-lines.

Using the box-cutter without the blade, compress the cardboard along the fold lines. I used my ruler to get them as straight as possible.

Image three is with all of the back-lines compressed - it might tear the back layer of cardboard a bit, just make sure you don't press too hard and cut through the front-lines.

Now gently pre-fold all of the lines including the tabs.

Do a "dry-fit" to get a sense of how the planter will fold together. We're almost there!

Step 6: Glue!

Using the Carpenter's Glue, put some small dabs on the tabs. Also prep some strips of tape to hold it together while the glue dries - I cut 6, but ended up needing about 12.

Using your finger (use latex gloves or a popsicle stick if you prefer) spread the glue evenly along the tabs for a solid connection. I used scrap cardboard to wipe my fingers of the excess glue.

Brace yourself, now is the tricky part!!! Start folding the pentagons together and make sure the tabs are making a connection on the inside of the planter. Using your finger and thumb, pinch the end pentagons together where the tab connects them, and quickly grab some tape to hold the flaps together.

Continue this pattern for all of the sides. I'll admit this part is difficult - just breathe in deeply and don't be worried if it comes apart at times.

If the connection isn't perfect (see picture #5 above), you can remove the tape for this connection, re-pinch the tab and get it back into place, and then apply more tape. Don't be shy with the tape, since you can remove it once the glue dries.

You should be left with the final shape of the planter. Feel free to move things around a bit until you're satisfied with how all of the edges line up.

Step 7: Finishing Touches (optional)

You could be finished at this point - but I like to add extra glue along the edges to smooth them out and add extra strength to the planter. Carpenter's glue dries clear and gives a pretty sleek finish.

See those rough spaces between the cardboard? Add thin strips of glue along them, then use your finger to smooth it into the cracks. The key here is to do small amounts, and wipe away any excess glue.

Go around the planter and get all of the cracks - if there are small holes where the glue dripped through, you can add a touch extra and smooth it out.

To get the top edge to have a nice seal, I added extra tape behind the cardboard to make a little dam, then filled it to the brim with glue. The glue likes to seep into the cardboard, so you may want to wait a few minutes and pour in some extra.

Go around and make it as pretty as you can by adding extra touches of glue, and wiping away any excess. I didn't bother with the bottom edges because you don't see them as much anyways.

Guess what, you're now finished!

Step 8: Let It Dry

Once it's dried (at least a few hours, a full day is better) you can remove the tape on the inside. I kept a couple strips just to be safe, and you don't see it anyways once a plant is in there.

You're now good to put a mason-jar with a plant in there. Or you can tape in a bag if you prefer... Or use this as a cast and pour in some concrete... You can also paint it any colour you like. The world is your oyster!

Congratulations, you've successfully completed this Instructable!

You can repeat this process with your own fancy geometric designs. Also, please comment if you have any suggestions on better cardboard techniques.