I remember making these when I was a kid, back when the 2 liter bottles had that little bottom cap as well. Recently, I learned about citrus plants and thought it would be really fun to try to grow a citrus tree from seed. Since I live in one of the mountain states, I knew I wouldn't be able to grow this outside. I needed a greenhouse. So I decided to reuse a couple of 2 liter bottles and make a small greenhouse for the early process.

Materials needed:
Two 2 liter bottles
Scissors
Utility knife
Flame
Soil
Seeds

Step 1: Acquire Bottles

This step is pretty self explanatory. They don't even need to be the same brand.

Step 2: Remove Label & Cut in Half

This is also pretty self explanatory. When cutting the bottles, I used the utility knife. Figure out how much depth you want for the soil before you cut.

Step 3: Taper One End

You will want the two halves to fit nicely into each other. Therefore, the top half will need to be tapered. Do this by holding the end 6-8" above the flame. Be careful, this will happen quickly. Just do it enough so it curls inside itself a little.
Once you have done this, check to see if it fits snugly inside the bottom half.

Step 4: Poke Holes in Top and Bottom

In order for good drainage of soil the bottom half will need holes to facilitate that. The top will need air vents as well.
To do this I heated a nail (do not hold it the nail directly or you will get burned) over the stove. I poked 3 in the bottom and 5 around the sides. I also did 5 small holes at the top of the top half.