I have used this same idea for many years, just a bit modified. I do not cut the end of the bottle off, but melt holes in the bottom & up the sides a few inches with a heated nail. Then I bury the end of the bottle that you cut off, leaving the bottle top sticking out. I remove the cap & till the bottle, then very loosely replace the cap. Same results, water seeps out at the roots of your plant. You have a great idea!
