I tried a couple of the designs on the web and was not satisfied with their confusing design or their use of tape. This design is held in place when you put the potting mix in it, and lasts until you put it in the ground, when it starts to break down. I modified this origami pattern. If my instructions don’t work for you, they get the same result as Hometalk.com, but I saw their instructions and didn’t understand them, so here’s instructions for brains like mine. 

1. Start with a small newspaper, like the ones full of ads that you mysteriously can’t unsubscribe from. Take one leaf from it and tear it in half, so you just have 1 page.  
   
2. Fold in half down the midline (horizontally). 
   
3. Open it back up and fold in half along the other midline (vertically).
    
4. Open it back up and fold all the corners to the center, which is where your previous folds meet. 
    
5. Starting with the bottom right corner, fold the outer edge to the center. 
   
6. Then fold the resulting edge to the corner as well. 
   
7. Open your last 2 folds back up and repeat steps 5 and 6 with the other three edges. It is pretty crumply now, but you will use these folds as guides. 
   
8. Open two of the opposite flaps. 
   
9. You should see a small square in the very center, made from the creases we’ve been making. This is the bottom of the box. We’re going to be folding up around this square. 
   
10. To bring two sides of the box together, we’re going to fold the corner in. The green lines represent “valley” folds (go away from you) and the pink is a “mountain” fold (comes toward you). If you look on the outside of the box, you’ll see how you brought the two valley folds together and they meet at a point. 
     
11. Lay that corner along the opened flap side. You can see where your pink corner should be.
     
12. Fold the other corner in by making two valley folds and a mountain fold again. 
    
13. Now we’ve got two out of four corners in place. Tuck the flap inside to hold our corners in place.
     
14. Using the littlest crease square as your guide, repeat on the other side to complete the last two corners. 
    

You did it! Happy planting.