Bottle Garden Edging
We collected bottles from friends, restaurants, etc. and used a bulb planter to make holes to stick the 'neck' of the bottle into. We have another bottle border in another area of our yard that we actually dug a small trench and planted the bottles much deeper. Both ways work very well.
The bottles are beautiful when the sun shines through the colors at different times of the day.
Check out the how-to here: