Just posting this in case it helps out someone else out! I have a preformed pond with rather narrow shallow hollows round the outer edge for marginal plants. Initially I used some of small plastic basket pots in these but they didn't fit in that well or give the plants much room to grow. Looking online I could see that aquatic bags were also available, made from some kind of synthetic mesh material, but that again the sizes weren't a good fit for my pond. So I a bit and decided to try making some for myself, using a black protective bag that had come with a handbag I had bought. It's some kind of polyester, a tough but fairly open-woven fabric of the same kind as is used in white to cover synthetic pillows and duvets. (Black obviously blends into the water better and if you don't have a handbag cover to hand, I'm pretty sure I've seen protective bags for clothes made from the same stuff in Poundland, etc.) You do need a synthetic fabric - cotton and other natural fibres would rot in the water. Having measured the depth of the pond shelf I cut the bag into suitably sized strips, then into squares. Then into squares which just need to be sewn together around three sides (or two, here - as I had started with a bag in the first place). I didn't bother to get the machine out but you could, if you were doing several. The stuff doesn't fray so it doesn't need a top hem. Again, use polyester thread as cotton would rot. Then I turned it to have the seams inside, put some crocks in the bottom to weigh it down, put the plant and soil in, and finished off with some pebbles to stop them floating away. They seem to be working well - less obvious to the eye in the pond than the plastic baskets: And the plants are growing away happily inside them now, with the roots beginning to poke through: So far the bags are holding up well, but if they do collapse it will be easy to hoick them out and find another solution, as they are so near the surface of the pond.