What to Consider
You may find
this article informative. Since you are focused on just Monarch butterflies, it talks specifically about that. Pretty much, this means Milkweeds, genus
asclepias.
If you want to create an actual garden, you can get a list of plants here on garden.org using the
advanced plant search to search for specific characteristics. Be careful with picking a minimum hardiness zone, you may eliminate plants that thrive further north. The caveat is that -- while you can mark plants that attract butterflies -- it doesn't specifically limit that to Monarchs.
The
Butterfly Weed is an excellent choice. It will grow in your zone, and is considered native according to
this web page on Kentucky native Milkweed species. You could pick anything on this list and be happy. It sounds like you've probably gone down this path already.
What to Pick
Once you have an idea of the options, you should decide where you want to put this garden. How wet is that area? How sunny is it? How big an area is it?
Then take a look at the plants you are considering, and eliminate any that can't handle the requirements. If it is a particularly dry area, for instance, Swamp Milkweed (
asclepias incarnata) probably won't do well.
I would recommend getting live plants over seeds. I have a packet of milkweed seeds I got, and I should have put them in the ground last fall, since they need the freeze/thaw cycle and exposure to moisture in order to germinate.
How to Arrange Them
The good news is that the milkweeds all like sun or partial sun/shade. That means the main thing you must consider in arranging your plants is how tall they will get; the plant database on here will tell you that. For instance, Whorled Milkweed (
asclepias verticillata) only gets about two feet tall, while Common Milkweed (
asclepias syriaca) can get up to four feet tall. Make sure that the Whorled Milkweed is more southerly, or closer to an edge of your harden spot, so it isn't in the shade of the taller plant.
You can start with a small, rectangular plot for now, or plan out a butterfly-shaped thing that may take a while to complete. Just keep in mind plant height and sunlight more than color.
Other Help
If you have any more questions, please don't hesitate to ask.
You may find more assistance on these garden.org articles:
Oh, a final thought: These milkweeds will be perennial. They will keep coming back. You may need to prune any old growth in the spring (I'd let it sit until then, as the stems can be winter homes for native bees, I believe), but you will get new growth from the taproot.
