Good question, Lapeer, MI. It's all private property, even the road, so I'm sure if its cleared with the neighbor that shares the ditch and as long as whatever I plant doesn't restrict the flow of water and flood my neighbors its all good

Not too crazy about the grasses, since that's pretty much what it looks like now.

If you live in Virginia, I can give you a couple dozen Stella daylilies.

I'd try Siberian or blue flag, but I wouldn't plant the yellow Iris pseudacorus simply because it is invasive. Your intentions may be to keep it under control, but you can't control what the critters carry away (such as seeds, its main mode of spread into wild wetlands), and there are potential natural or life emergencies that might prevent its control. The water in your ditch is most likely flowing to somewhere which will be off your property. Since I deal with removal of a lot of invasives, I wouldn't want to plant them in case I couldn't keep them under wraps.

Many kinds of daylilies are moisture tolerant, as are both Great Blue Lobelia (L. siphilitica) and cardinal flower (L. cardinalis.) Marsh marigold (Caltha palustris) is a spring-bloomer in wetlands, and if it gets too dry in summer the leaves will die back until the following spring, but it will stay green all season in ordinary garden soil. If you want shrubs, there are some of them that would love the prolific moisture as well.

What kind of height are you looking for? I have some ideas, but some things get pretty darn big....

I definitely don't want anything huge. The current grass in the ditch ranges from 2-3 feet. I wouldn't want anything bigger than that

Cinnamon ferns might even be happy in full sun with that kind of moisture. Also Japanese iris, Louisiana iris, and Iris virginiana. If you can do shrubs, Clethra would work as well.

ditto to babs and laceyvail. Astilbes love it moist - don't think they would like the standing water, but perhaps along the edge of the ditch...

I updated an existing garden that is under water for parts of the year; it is at the base of a hill on one side, with a creek that runs along it on the other side. Often it has standing water for weeks on end, of at least 6 inches (I lost a shoe in there once, lol - foot came right out of it when I went to move!). I ended up planting a lot of shrubs, as this is a large area and we were looking for big things. I also wasn't planting right in the water flow, as it sounds like you may be doing, so that will affect what you plant compared to what I planted, but still, maybe this will be of some help. I'll list below (from hopefully-good memory) what we planted.

- willow hakuro nishiki - probably way too big for you - I planted two of them, just to give you an idea of the large area I was dealing with. These are spectacular, though, IMO, if you wanted to consider one of them as a specimen...

- astilbes

- japanese and louisiana iris

- clethra

- itea

- cephalanthus (lovely and underused, IMO, and some new dwarf (4-ft) varieties out there now, I see

- redtwig dogwood

- viburnum (probably too big for you)

- deciduous hollies (again probably too big for you)

- marsh marigold

- bog rosemary

- lobelia siphilitica and cardinalis - the siphilitica is truly beautiful, but I would not plant this again - very vigorous spreader and I just don't have time to maintain/control. The cardinalis is spectacular (and I don't even care for red blooms!) and I highly recommend this one.

- ligularia

- filipendula (can't remember which kind off the top of my head)

- cimicifuga

- swamp azalea

- marsh hibiscus

Already in this garden and doing surprisingly well were bleeding hearts, hosta, hydrangea, peonies, columbines and some kind of small bulb which I'm drawing a total blank on at the moment - like a scilla or something... ugh, sorry, can't think of it.

And of course there are ferns, which were probably there before any garden was even thought of! There is also an elderberry which pre-existed the garden - this is along a wooded area so some things were growing there already, such as the elderberry, ferns, a clethra, etc. (plus virginia creeper, jewelweed, pokeberry, sigh....)

I think that is most of it. Good luck to you!

OP i have same issue but i am in East Texas, what did you finally decide on and do you have a picture. :)

I ended up doing nothing at all, yet. I am thinking about putting a Hakuro Nishiki willow in there and seeing how it does. If it succeeds, a 300' row of that separating our yard from the neighbors would look amazing. Especially with my new row of 6 Autumn Blaze Maples right in front of it.

I had a Hakuro Nishiki willow that did wonderfully in a wet shady area. Until the deer destroyed it! Have you considered ditch lilies? My neighbor has them where there sump pump drains and nothing kills them.