Welcome to 2-liter gardening.
Curiousity, a desire to add a garden to that small space, or just because it looked neat. Whatever the reason that brought you here, Welcome! I like to find new ways to use objects and with all this, "save the planet," stuff I thought I could probably come up with something to help that cause. I'm a design drafter, by trade, that works for a company that focuses on buiding displays out of steel wire or rod. It occurred to me that steel wire would be a great way to and some strength to some on the 2-liter designs I have seen online. I came up with some designs and put them together on this website. I hope you will find something that will help you to make your space a little more "green."
Alright! You are still interested in what I am talking about! Then I will continue...
      Before you put your plants into their new home, we need to make sure it is ready for them. Start by washing out the 2-liter bottles that you are going to use. I made the mistake of skipping this step and was rewarded with ants. Once the bottles are clean, I have seen three ways we can make them into useful planters. I call the designs: VT, HZ, and WS.
 WS Design
      Let's start with the design that got me hooked into this crazy ride. The designer call it a SIP (sub-irrigated planter), but I call it a WS (water saver) because it saves the water for the plant without drowning the roots.
(a link to the designer is below the image)
Link to SIP designer page
      VT Design
      A nice and easy design that I call VT is created by cutting off the bottom of a 2-liter bottle. You can poke some hole in the cap or just have it loosely screwed on to alllow drainage. This design is great for plants with deep compact roots. Believe it or not, I have grown carrots in this design.
      HZ Design
      This is the design that seems to get the most, "Oh, that's neat," reactions. It is not as simple to make as the VT design, but it is easier than the WS design. This design also tends to have the shallowest root support. Herbs and ground flowers work great.
      In order to make this design, you have to first know where your hooks are going to hang. The Indoor HZ starter kit was designed with the 2-liter bottles from coco-cola in mind. Putting the hooks at about 9 1/2 inches apart seems to work the best. Once you know where the hooks are going to go, use a utility knife to carefully cut a half circle kind of shape between where the hooks will be. When you have the shape you want, add some double side foam tape where the hooks are going to be to help prevent shifting. Add the hooks and hang it up.
      Sometimes I have to add a few stones to neck end of the bottle to help balance the weight if it is hanging crooked.