I have found new use of the upper part of plastic bottles, after cutting them. The lower part is used as planter by making holes in it. The upper part is inverted and put inside soil till it becomes stable. You will have to make some holes in it near the bottle cap for improving drainage.
After these bottles are inserted into ground, put some kitchen waste into it till one third height. Mix with soil. Put soil till the top and pot a plant which does not need much root space. I have chosen marigold.
While watering, the excess water goes to the bigger pot and thus reduces wastage.
In the photo, you can see the hibiscus plant in the main pot and marigolds growing in recycled pots.