Have you cut some bottles for another project and then wondered what to do with the tops you have left over? I made some plant watering bottles out of a few of mine and they work great! I started with the cut off tops:
I then went to a planter I have that is lined with coconut fibers and pulled a small batch of fibers off to use in these tops:
Stuff the fibers into the neck of the bottle, being careful not to cut yourself (voice of experience talking...). You want to pack the fibers in fairly tightly to slow the water down as it drains through the neck of the bottle.
Place the bottle top next to a plant you need to slow water, fill it with water and let gravity do its work.
If the water drains too quickly, stuff more fibers into the neck. After all, this is a s-l-o-w watering system.
Hope this works for you as well as it does for me.