The only one I’m really familiar with is Carex pendula. While it’s a statuesque native here and flourishes in damp gloom where not much else will grow, it is also an enthusiastic self seeder. They are most definitely perennials.

I have "Ice Dance", and I've never noticed it seeding, but if it's happy it will spread outwards to form a really big clump. It's easy to divide though. That's the only carex I have experience with so far.

I have had muskingumensis 'Oehme' seed. The seedlings do not have the variegation. If I had time I would remove the seed heads.

I would check to see which carex plants are native to you. I had some lovely small ones put in along a dry creek bed by a landscaper years and years ago. They are now monsters and have filled in the entire side garden! Wish I could tell you which kind they are, but I can't. Just be ready to divide every couple of years. They are, nonetheless, lovely.

Some carex may require dividing - many do not. I have clumps of carex that are many years old that never get any bigger. And some varieties tend to be rather short lived as well.

Research thoroughly whatever species and cultivars you are considering, as preferred growing conditions, behavior and habit can vary widely among them.

Lots of helpful information here--thanks. I am looking to use one species as a matrix from which taller plants will arise, so there will quite a lot of the one species. Any suggestions as to what Carexes might be best?

i wouldnt underestimate the difficulty of dividing carex. it’s a chore i hate.

Do you know what ones you have that need dividing? It can't be any worse than dividing Sporobolus heterolepsis, which was a nightmare.

I have "Ice Dance", and I've never noticed it seeding, but if it's happy it will spread outwards to form a really big clump.

@porkchop_z5b_MI echoes my thoughts. I do like this plant lots.

Izel just wrote a blog post about sedges. https://www.izelplants.com/blog/getting-sedgy-with-green-mulch/ I planted Carex albicans last year as a matrix, but it hasn't been in the landscape long enough to really say much about it. I also planted Carex blanda 2 years ago, and have Carex rosea and Carex sprengelii waiting to be planted, which are also clump forming sedges that can tolerate dry shade. I have Carex vulpinoidea on my property which came in by itself, it is a plant that some sources say self seeds aggressively, while other don't mention spread, I think it depends on how happy it is with the conditions.

Some sedges like Pennsylvania sedge and Carex stricta can spread via rhizomes, sometimes aggressively.

Carex blanda on the left

Carex blanda. This one is known to seed around a bit but the seeds are held low, maybe ant or animal dispersed, and I haven't found any seedlings yet.

I have grown a wide variety of Carex and have never had problems with these seeding. But they need to reach about three years of age before aggressive seeding is even possible. Only some species self-seed, such as Carex divulsa. The varieties you see commercially available, like Carex oshimensis 'Evergold', rarely self-seed.

Those who like Carex might also want to study Lomandra longifolia, and the variety I have and really love is "Breeze"

https://plantclearance.com/products/lomandra-longifolia-breeze

I had a lot of issues with other grasses I ordered from Plant Clearance, but their "Breeze" is a superb plant.

It's been several years since I first posted this. I've got several carexes that are doing well and that I'm happy with and at least one that was too vigorous a spreader and had to be removed. Carex greyi and C. pennsylvanica are the only two whose names I can remember offhand. Both are doing well but C. 'Feather Falls' is eaten every winter by deer and never recover well. Only one is left.