Umbrella palms are a wonderful means of shade, a place for your turts to bask and don't require any dirt to grow in. You do have to create something big and strong to hold them down in though, because they will get huge over the years.
When I started mine about six years ago I submerged just a small plant with a root system about the size of a fist in a 20"plastic planter with half a cinder block inside of that in the deepest part of my above ground 145 gal pre-formed pond.
The roots were in a plastic mesh to contain them and that was placed on top of rocks I put inside the cinder block. This allowed the height level I needed for the roots to be submerged and the top of the plant only to be out of the water. I also positioned some flat shale rock on top of the cinder block around the plant to hold it in place and make it turtle proof.
Once these plants take off, the root system as well as the plant get big. The roots in mine have completely filled the planter and have gone over the sides. The whole thing appears to look like a stump at this point with shoots coming out everywhere.
When the palms get tall (3 feet or so) the planter can be blown over under heavy winds and that's why having them in something heavy is a must. Trimming them back helps too. They are fast growers in the summer and are dormant in the winter.
My turtles love theirs and it makes your pond look good too!
Good luck ... fric
