Take a circle of fabric (depends on the size of your planter) put a wad of batting in it. Gather the fabric around the batting to form a ball. Sew a few stitches to secure. Stuff it into the container to check for size. Might have to add or remove batting for a good fit. When it looks good, remove it and apply hot glue about a half inch below the edge of the pot on the inside, all the way around. stuff the ball back into the container. I have had better luck with a bit sturdier fabric. I really like cotton velveteen. I also like using wool batting.