You can use either of the options for planting in the bottle towers:- Option 1 (soil medium) :- Use 1/3 rd soil, 1/3rd coco peat and 1/3rd compost. You may add some vermiculite and/or pearlite to improve porosity and water retention capability. Option 2 (hydroponic medium) :- Use 60% coco peat, 20% vermiculite and 20% pearlite as growing medium. In this case nutrients are fed through solution in water. Fill the lower 2 inches of the bottle with pebbles to ease in drainage. Then fill the growing medium upto the cut slot. Plant the saplings in the medium. A number of bottle towers can be combined together. The bottle towers can be mounted on a suitable steel frame. Use a 75mm or larger sewer pipe to collect the drain from individual bottle tower. The two ends can be closed using end caps. A drain pipe from this can be connected to sump. The plants can be watered manually from the top bottle of the tower or use a timer controlled drip irrigation...