I have an 18 inch wide area between a 6' privacy fence and sidewalk I'd like to plant with something better than grass. The approximate length of the area is 260 feet. I'm in Madison WI, so zone 4ish, but this location faces directly south -in the photos standing on the sidewalk, you're looking directly east, with the fence facing south. So it gets a lot of sun all year. Those areas in the terrace are rain gardens with native plants the City installed. The soil between the fence and sidewalk is very free draining - There's a retaining wall within a few feet behind most of the fence, and that has gravel backfill behind it, and the sidewalk has sand fill under it as well. This whole area is actually built up several feet using a very sandy material when they built the sidewalk/street/retaining wall. This street, the area you see to the east and the apartments on the other side of the street to the south are all built on a former limestone and sandstone quarry. So the planting bed has maybe 4-6 inches of topsoil with sand and gravel beneath that for several feet below that.
That's my house in the last photo, behind (and lower several feet) the fence.

A few wishes on my part -
plants that are easy to maintain once established because it is a lot of area, even though it is narrow. I may use stone instead of mulch, but have both in my yard in various areas, so either one would be ok, although weeding mulch is not as easy.
something I can cut back, or push out of the way easily, in spring so I can continue to maintain (ie stain) the fence every several years without plants being in the way too much.
Something not too tall, since I don't want it to hang over onto the sidewalk much, if at all.
Something perennial, because I don't want to replant this every year.
Something I could either buy in bulk, in plugs or small plants, or seed because buying all potted perennials for this would be pricey to do, although I'm not opposed to doing portions of it over several years, as long as I have a plan for how the whole thing will look when finished.
Preferably something native to WI if it is a perennial.

I've thought perhaps purple coneflower and black-eyed susan combined together, but am looking for ideas, as that is pretty generic. But at the same time, it is always a nice combination. I've also thought about using ground cover of some kind, or sedums.
Any input would be appreciated!

Those two were top of my mind but there's also columbine which blooms in the spring and attracts hummingbirds. I also like catmint, walker's low is a favorite here, and salvias are great too. I know there are shorter cultivars of sedum that won't fall over like the taller ones will. There's also mums for fall and new england asters. I'll see what else I can think of.

Here's a list from Prairie Moon Nursery. They specialize in natives and are a good source to talk to and buy from. Coreoptis is listed also. That's a great plant and I have it in several spots.

https://www.prairienursery.com...

Since it's such a long skinny area, I would recommend a tall skinny reed grass. Karl Foerster is a very popular one in contemporary plantings especially in beds similar to this one. You could break up the monotony by doing sections of like 5 plants with sedums or something in between. I personally think sedums and Karl Foerster pair well together. The reed grass would also give a lot more height than other perennials, but could easily be chopped down for fence repairs!

Here is something you might want to consider...

Espalier is a great way to decorate a vertical space without taking up a lot of horizontal space... and it looks great year round..................

The plants in these photos are hardy in zone 4..............................
A few examples:

Fruit Trees bloom in spring... and have edible fruit in fall...................


Climbing Hydrangea is stunning when in bloom.................


and Spruce cultivars [especially weeping varieties] can be trained in this way..............