Hi, I haven't seen any semi circle planters. Something you might want to consider using 3 to 5 different sizes of terra cotta planters with different types of flowers to give you different heights and textures. I do this throughout my garden and it looks pretty cool.

You could also try to control the ants using one of the baits that is organic and safe like Green Light. They "feed" the control to the ants so they take it to the queen and affect egg production. While you are waiting for the bait to work you could put a few sedums in there to cover the area. RJ

Here is a link that might be useful: Control Fire Ants

I've seen those type containers for mailboxes somewhere in a catalog..will see if I can find it for you. Did you try an internet search through Google or Yahoo?

I bought one of those wrap around pots for my mailbox post about three years ago from "Domestications" It is actually 2 half circle pots that fit together around the post and clip together with toggles. The post is completely isolated from the potting soil and water. They are so big I half filled them with bricks.

They can also be used individually against the wall or a porch rail.

i simply made a bottomless box from treated wood planks and lowered it over my mailbox. i mixed potting soil with regular soil and stuffed the box with all kinds of flowers, including a carolina jessamine vine. somehow a crepe myrtle snuck in there, so i keep it nicely trimmed. there are so many flowers that you can no longer see the box.

i doubt if a homeowners assn would approve of such a simple wooden box, but it wouldn't hurt to find out.

Something to consider too. Could your mail carrier(s) be allergic to bees?? I always think of that when I see flowers around mailboxes because I'm allergic and am terrified of bees.