Christie, my 3 Azaleas came from Wal Mart. They have all done very well ( until the pink one was frozen very badly last year).I did not amend my soil. It is already acid, and wild azaleas grow down in our hollow by a pour-off.( I transplanted one into my yard under a bladdernut several years ago. It has lots of blooms right now! )
My white one is so large I have to prune it back after it blooms. It is over 5' tall and 8' wide. I have had it at least 15 years.It was a gift from a dear eldery friend.
I looked for a label but can't find one. :-(
The white one holds it's leaves all winter. The pink and red ones do too, but not as well.

Here is the white and the pink 2 years ago:

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They are on the northeast side of our house, by the deck.

Below is the red one, also a couple of years ago. It is on the northwest side of our house.

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Hi Christie,

Paul James does a great job of summarizing azalea care:
http://www.hgtv.com/hgtv/video_guide?q=azaleas

I, too, am in awe of the beautiful azaleas all over town. Have tried to grow in AR without luck, but will try again here. The key is the soil.

Here's a link to some information about growing Azaleas that may be of interest. Also lists the general hardy types for MO.
I grow hundreds of them, but I also have some failures. Not everyone you plant will thrive in every location in the garden.
Good luck!
Rb

Here is a link that might be useful: Growing Azaleas & Rhododendrons