Sedges have edges and rushes are round.
I think I learned that line in high school. Sedges, like grasses, have flat, long leaves. But unlike grasses, they have three-sided stems with edges. Rushes, which also resemble grasses, have long, thin, round needle-like leaves that usually stick more or less straight up in bunches.
This sedge is probably tall flatsedge, Cyperus monandrus. Most gardeners pull these out right away, knowing they can incredibly invasive. But in this deep nature garden, many otherwise invasive plants are allowed to get a small space of their own. This tall flatsedge has a nice semi-shady place. It has built itself into a lovely little clump that attracts various interesting critters.
If you decide you’d like a small (or large) clump of sedge in your nature garden, here’s a bit of advice. If you don’t want to be pulling out thousands of sedge sprouts, cut off the seed heads as soon as they are ripe.
Here’s an idea: display them in a place that their seeds will not spread all around the garden. How about mounting them near a bird feeder, maybe over a cement deck? Little birdies like to eat sedge seeds.
Or you could be a fanatical deep nature art gardener like me and enjoy the beautiful seed heads as they naturally age in place — and I guarantee you’ll be pulling out sedgelets forever, just like me.