If I am thinking of the same thing you are, I would think you could make it with expanding Great Foam (found at Lowe's or Home Depot).

This is how I would do it:

1. Use just about any piece of sturdy flat plastic or dense foam as a base and cut to the shape I wanted with holes cut for the base of the flower pots. (to allow water to get to the plants).

2. Place the pots where I wanted them and put the foam on the plastic and around the pots. (If you haven't used great foam before, spray a very small amount first and watch how it expands to get an idea of how much to use to start with.)

3. After the foam has hardened, I would use saws, sandpaper, knives, etc to give it a rock shape.

4. As far as I know, Great Foam comes in white and black. If you don't want either of those colors, you can use latex or acrylic paint to paint it the color you want. As a matter of fact there is a product on the market that is a spray paint that looks like rock. I don't know if it would be toxic or not. If it is latex or acrylic, I would think it would work.

5. Another option would be to put sand or very small pebbles on the Great Foam before it hardens. That would save the time and trouble of carving, sanding etc.

I wear two or three sets of rubber gloves when working with great foam as it is VERY MESSY. When a glove gets too covered, I just pull it off and there is a clean one underneath.

Good luck. Sounds like you have a good idea. Post pictures when you are done. Below is a thread of other floating island ideas.

Here is a link that might be useful: Floating Islands

I built a floating island this winter. It is great because it gives the fish a place to hide. I bought a large sheet of pink foam from HD. The pink foam works much better than styrofoam. You can easily cut it with a skill saw and sand the edges smooth.

Here is a pic before planting and a pic after planting, I still need to add a few more plants. I cut three large holes to slide pots into and a bunch of small holes for bare root plants like creeping jenny and watercress. No rocks on mine but I see how easy it would be to stick some on top. Especially if you used the thicker foam than I did to keep it afloat. The first picture has plastic plants shown in it, but I have since removed them.

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I anchored it with a string and rock so it wouldn't move around.
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(By the way, those pictures are out of this world.) The foam that they make pool toys (noodles) and kickboards sounds definitely like the thing to use. Wood or cork could rot.

Thanks for all the suggestions. I have been surfing and found some other info on floating rocks that look realistic. Styrofoam covered with hydraulic cement. Used in zoos and not poisonous. I got some foam today and now I have to find the cement.

Hopefully this isn't too late. We have 2 floating rocks in our pond. We basically took a couple of milk crates, cut out everything but the frame on 2 sides. We then covered the other 2 sides with pond liner and placed in the pond. We then place a large piece of fieldstone on top. Works great. The frogs love to sit on top in the sun, and the fish (at least when they were smaller) love to swim through the tunnel. If you need more height, just stack the milk crates.

Carjeff - that's a great idea. I might just use that myself. It would look good in my little pond.

pcan - Your island is just fabulous. I am impressed that it is still floating. That must be pretty good foam to hold all that weight.

Amazing!!

Love the pond! I have a rock that is stationary....but looks like it is floating LOL...took me a few stones underneath and maybe a few budlights...too LOL!! Dave in WV!!

Small world. Pcan, saw your pictures in a different form, saw your island and it got me to thinking about floating islands and here you are. In the first forum I didn't realize this was a floating island.

Carjeff, I am trying to make the milk crate rock island. How did you attach the pond liner to the crates? I tried zip-ties, but they are sharp when I cut them off and I didn't want fish or others to get scratched on them. Got any pictures? Thanks!

-Jo

haven't tried Pcan's idea but having tired several others including the use of Great stuff foam, I"d bet the foam via pecan is now the best way to go. Remember you can add an additional layer of foam under the base to increse the bouancy of the island easier with than trying to increase bouancy via great stuff foam - and no mess. Mess - been down that road.

I'd try Pecan's idea, but I don't have not room for an additional island - next project is a water wheel

Has anyone tried growing moss on their foam island? Will moss survive in full sun?

Regular "I need shade" type of moss wouldn't do too well unless planted under something that would provide shade, but Irish or Scottish moss would probably thrive as it loves sun and moisture.

You should be able to find it at a local nursery (not the Lowe's type - I've never seen it there) or on line.