I am not real sure about this, but I suspect in a few years the grasses would do the same thing as the hosta's...over running the patio and leaving much debree...I think they would be pretty and soft and wispy..but if you don't like the messy look...I am not sure grasses are the way to go...just my thoughts..

Can you soften the square by curving the bed area??? Maybe some low growing flowering shrubs mixed in with grasses. Then add things that will bloom during the time you can use it. A small walkway from the concrete out to the yard through the bed would be nice. Lots of stone/rock/brick options.
Here's some things I have planted with my grasses:
potentilla
hydrangea
daylillies
low growing spirea
sedum (autumn)
Russian sage
small evergreen shrubs

georgeanne
P.S. Don't forget wonderful garden "art".

I don't think the grasses would necessarily be messy. I only have a miscanthus zebra in my garden, along with some sedges which are very grass-like. I don't notice any debris from them. Best of all, they give great winter interest. The sedge is low-growing, and I have a weeping variety that will cascade over the edge of your patio and soften it a bit.

I think MrMorton has a nice collection of grasses, so he should be able to tell you some companion plants.

Tracy

I agree with georich's idea of curving beds to soften your square patio! Curved beds add a lot of interest and give you more depth for planting.

I've had good luck with two particular grasses and since we are both in the same zone I think they would be a good choice. I love Feather Reed Grass 'Karl Foerster,' which gets about 3-5 feet high and 1.5-2.5' wide. It gets beautiful wheat like plumes in summer and still offers winter interest. My other favorite grass is fountain grass 'hameln,' which grows 1.5-2.5' in heighth and width.

Planted near my grasses are heuchera, astilbe, catmint, coreopsis, salvia and I use some ajuga for groundcover. I know some people complain that ajuga can be invasive, but in zone 5 I don't find that to be true. This past winter nearly killed a few mounds of it!

Good luck!

Here is a link that might be useful: Feather Reed Grass

What about some veggies those pretty cabbages with some short ground cover flowers?

hakonechloa wants shade. Blue fescue is a wonderful little grass.

I have a patio border garden--also about ten feet long, but deeper than yours (more like 3.5 feet). I have lots of Elijah Blue fescue and Sedum spurium (tricolor stonecrop)--I think it's a great combination. I also have two miscanthus Adagio--recommended by someone on this board. As well as a Hameln. Hakone grass is great but needs some shade so may not be the best choice for you. Good luck!

Wow! Thanks for all of the great ideas! I especially love the idea of curving the beds around my square patio. For some reason, that had not really occured to me. Too much time in the sun perhaps?

I have a Karl Foerster Feather Reed Grass which is not messy at all. It does well in full sun, but does need constantly moist soil. Other Feather Reeds, such as Korean and Purple come to mind. Sedums, Rudebekia's (not just Black-eyed Susans), Ligularia, and other prairie flowering plants would be good.
I'm not big on blue grasses, but Blue Fescue is another popular grass that does well as a border plant.

ntaylor,
I love your herb idea!
I wish I'd thought of that when, I put in my patio beds.
My herb garden is in my potager...waaayyyyy across the yard.
I'm always running out there with things on the stove!
My beds are so full there, something would have to go
now. Live and learn!

Haziemoon

I like the idea of surrounding the patio with a curved bed. Use a mix of grasses with different heights and colours. Soften the edges of the patio with creeping thyme which look great against grasses by the way. You can also add large and small rockeries for interest. Avoid uniformity and always add different groupings. Add plants with different leaf textures. You should know that some hostas do thrive in full sun. so don't be in a rush to remove them. You can intermingle them with the grasses you want. And don't forget lighting. What a lovely scene this could be at night. A patio table outside, small romantic spotlighting hitting those tall grasses. Sounds the grass gently swaying in the wind.

Ianna