Hi Everyone: This is my first post on any Garden Web forum. I'm a wet-behind-the-ears market gardener and currently I'm working on plans for an irrigation system to be used in my 2013 garden. I'm considering recycling 2-liter pop bottles with gravel and pin-sized holes in the bottom for slow release watering. While I've found lots of info on how to make and use them, I've yet to find info on how much coverage they provide. I realize that a larger container will provide more volume, but I'm wondering if anyone can provide me with a more specific idea of how many bottles are needed to irrigate an entire raised bed. My raised beds are 12" deep, 4' wide and 12' long. How many of these bottles do you think I would need to irrigate an entire bed?

Thanks in advance for any insight you can provide!