I've been intrigued lately by the idea of "wicking beds" for gardening, so I decided to have a go at it on a small scale with one of these "global buckets" style setups. The gap between the bottoms of the nested buckets forms a reservoir, which can be replenished via the standpipe. There are overflow holes on the outer bucket to ensure that the water level always stays below the floor of the inner bucket, and allows air beneath to prevent root-rot. The soil retains moisture via capillary action from the soil in the cup, which is immersed in the reservoir. Pretty basic. I'm curious to see how it performs and how often I have to top it off.