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kind of sounds like the idea behind the "Earth Box," but I'm having a hard time visualizing your setup.

http://www.instructables.com/id/Building-your-own-Earth-Box/

 

It shouldn't hurt I think. Are you not able to get to the plant regularly? Why is it important to conserve the water?

 

actually ive been doing that for this grow since ive been traveling alot, and cant water them all the time... but it doesnt really help the way you have it (atleast for me). what i did to solve that problem is i transplanted the plant into a slightly bigger pot, but the inner wall of the new pot is lined with a cotton towel that goes down into the bottom reservoir so the water travels up the towel and keeps the soil moist. no this is not just a theory, i have the setup, it works!