Plastic Bottles instead of Pea Gravel Pea gravel and pebbles can weigh down window boxes. Empty water bottles are a lightweight option. Place rinsed bottles inside the planter and add soil on top of them. The space between the bottles will allow proper drainage without the extra weight.
close up of mosiac window using colored broken glass and adhered using a silicone base clear gel. This particular adhesive is waterproof, so can hang it outside in garden. It would only cost a few dollars..