If you are planting in the position the pot is now it looks a bit shady to me. I suggest if you get 4 hrs of sun in that area I would plant a

fairy rose it blooms all summer and a purple Herchuera. To compliment your red japanese maple. This is not a good pic but I have that combo in a raised garden. It should be hardy in a pot.

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If you do not think there is enough light maybe....
Creeping Jenny and Sedum in the middle. I have a green and yellow sedum that is tall as Autumn Joy it blooms pink in the Fall. If you want I will look up the name of the sedum.

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any annual vine... sweet potato???

or clematis???

something to work off that railing ...

ken

Thanks for your suggestions. I would love to have a Clematis to cover that railing but it would be fruitless since the railing is going, soon to be replaced by a more modern white railing. Hubby would scream bloody murder if I attempted to cover up his handy work ;). I like the idea of some creeping jenny hanging over the side of the pot. I'll have to think on this one a little longer.

Thanks everyone.