Sub-irrigated planters (SIP) are simple devices that allow low-maintenance, low-water consumption container gardening.
Construction
A simple SIP has three major parts: a container for soil, a container for water and a wick that allows water to be drawn from the water container into the soil container.
This diagram shows the major parts of a simple SIP made from a plastic pop bottle.
The wick (typically made of fabric or polyester) draws water up into the soil through capillary action.
Aeration holes in the soil container, combined with overflow holes in the water container, help prevent the soil from becoming too wet.
For instructions on making SIPs from plastic pop bottles, visit:
http://suresimple.blogspot.com/2009/04/recycling-juice-and-pop-bottles-as-sips.html