Thank you for that information. I planted my Washington State Centennial in amended native soil with 50% compost/pine bark fines and 10% Turface. I elevated it above grade so the water would not collect in the root zone. I'm assuming it's standard growth for all azaleas that the roots are shallow?

So how deep would you suggest digging? There is concrete on both sides that runs down about four feet but the garden bed itself is about 30' x 6'. I'm afraid of elevating the roots too much as zone 6 is the minimum it will survive and we have had some extreme cold snaps in the past. Of course I'll mound it above grade somewhat, I just worry with it being too exposed. As far as the mixture you're suggesting, just so I'm correct, the pine bark fines, Turface and pea gravel and that's it? No compost or native soil? What ratio of each would you suggest?

How deep depends pretty much on how high above grade you want to go. If you excavate 6" and go 12" inches above grade for a total of 18", you should be fine. Even 9" above grade ought to be enough. I don't think depth will have much, if any, effect on hardiness. Rhododendrons and azaleas have wide (eventually) shallow root systems. In Z6 and colder they certainly experience sub freezing temperatures in a normal winter. For deciduous azaleas like austrinum, frozen roots are much less of an issue than they are for evergreen rhododendrons and azaleas. As with any first year planting, some protection against sun and wind would be helpful even though in this case you would be protecting bark and buds rather than leaves.

i did not mean to suggest that there is any reason not to use some of the native soil and some compost, although make sure the latter is not too high in nitrogen and is acidic or only slightly alkaline. I do have reservations about the pine bark fines. This is a major component for the 5-1-1 mix and gritty mix in the container forum. What makes a good fast draining mixture for containers is not necessarily useful when used in the ground. Fines will break down much more quickly than standard bark mulch. You're wise to avoid perlite. It's not needed and eventually floats to the surface and washes away. If you can get the dark partially decomposed kind of bark mulch with fine and larger pieces, use it instead. If you can find it already mixed with compost, even better. The pea gravel is purely a suggestion. With your summer temperatures, bark will tend to break down and compact pretty quickly. The gravel will help avoid compaction, but you will still have to add mulch as the original mixture breaks down.

Just as a question are deciduous azaleas so uncommon in Kentucky? It sorta seems like you are going into overkill to grow this plant. Mainegrower's advice is perfectly valid and correct; but if you are not seeing such shrubs around your neighborhood I'm wondering if the problem is more alkaline soil than clay soil. I've seen 'Gibraltar' planted on, basically, plain red clay at an old Virginia farm, and the plant was doing fine. Granted it was a well draining spot.

We do have very alkaline soil here. I counteract that in my gardens by using lots of organic matter and follow a routine application of Tiger 90CR sulfur. I regularly test my soil to know what pH I'm working with. I've had great success with a previous deciduous azalea planting, this particular one just caught my eye. There are lots of plantings of deciduous azaleas in my area, but none wild that I know of. Rhododendrons, yes, but not deciduous azaleas. Just to my north, a former nursery owner grows an extensive collection of azaleas and rhododendrons. The majority of those are in raised beds.

As far as the recommendations for bark and pebbles, I will take that advice and use it when planting this shrub. I know I can find larger pine bark pieces to use, that's no problem. I was only finding those everywhere when I originally was trying to find just fines. Thank you for your knowledge and time in this akamainegrower.

Ok...now it makes more sense! of course the Gibraltar I mentioned here is the well-known orange Exbury hybrid.