This a relatively simple modification to the planter described in Modular, Windowsill, Air Powered, Hydroponics Herb Garden/Experimenter, step 6.
I have a problem with my seedlings being eaten by cats when indoors and being destroyed by high winds when outdoors on my balcony. To prevent either of these things from happening I have used 2L Pepsi and 2L Coke bottles in conjunction to make this. It can also be used as a terrarium for small plants or seedlings.
Step 1: What You Need
1 ea 2L Pepsi bottle
1 ea 2L Coke bottle
1 ea Utility knife
1 ea Drill
1 ea 1/8 inch drill bit
Step 2: What You Do
1. Cut the bottom off of the Coke bottle.
2. Drill holes in bottom, invert and place in bottle top as shown. Planter done.
3. Cut Pepsi bottle in half.
4. Place top half of the Pepsi bottle onto the planter, sliding one bottle inside the other like a sleeve.
5. Fill with grow medium, plant plant/seed/install dome and wait.
Note - To have sleeve slide down the outside of the planter, rather than the inside. Make the Pepsi bottle into the planter and the Coke bottle into the sleeve/dome.