how do I get ostrich ferns under control?

Question

The ferns are very tall and taking over all other plantings around the water feature.

Answer 1

You can always dig up the clumps and divide the rhizomes to share with others. Also, in the spring as the new fronds emerge, the ones that stay shorter will have the spores on the back. Removing those fronds may save you from a bunch of new ones grown from spores. Here is more info:
https://www.gardeningknowhow.com/category/ornamental/foliage/ostrich-fern