[header] How to build a window farm [title] Have one empty bottle for each type of plant. [title] Cut off the bottoms of each bottle with the blade. [title] Hold each bottle inverted (neck down) and place a few clay fired pebbles into the bottles through the sliced-off bottom. 
[step] If the pellets have a tendency to fall out of the bottle's mouth, place a piece of cloth in the neck and then add the pebbles. These pebbles act as soil, holding enough water for the roots and also allowing for air to pass.