The following should work for you. It is based on some 'playing around' projects I have been working on with great success.

1. Purchase a roll of landscape (weed barrier) cloth. It should be the type which has a sort of black, velvety appearance on one side. This runs through a sewing machine with ease. Sorry, I can't remember the name of this particular landscape cloth at the moment.

2. Cut out a piece the needed height and length for pot side and sew the seam together.

3. Now, cut a circle and fit plus sew it to the bottom to complete the 'bag'.

4. At Walmart's notion counter you will find a waterproof glue designed to attach beading to garments. This works well. There are other types of glue but this one is my favorite. Glue all seams with this.

5. Cut a circle of heavy plastic to fit inside bottom of bag.

6. Dig hole for bag placement, insert bag, add soil and plant.

I can assure you that these will last for years. Once you begin working with the construction you should be able to figure out the method which goes together quickly. It is possible that you may want to fold over and sew the top of the bag for rigidity.