I don't live anywhere near limestone but there is nothing particularly unique about Encore azaleas......other than they are repeat bloomers. Like any of their species, they want well drained, moderately organically rich and acidic soil. They need significant irrigation for their first couple of years of establishment and in hot summer climates, would prefer some afternoon shade.

Your biggest issue may be soil pH. An insufficiently acidic soil will not kill them but will certainly affect performance and appearance.

You will need to build up a bed with rich soil and add cow manure and peat moss. Then fertilize regularly with a high acid fertilizer. But if you're doing it in San Antonio, better hurry up before it gets hot. You'll have to water throughout the summer to have them live..

In the Dallas/Fort Worth Metroplex, Encores in morning sun or dappled sun perform very well but our alkaline soil (pH 7.6) soil is not as limestone rich as yours is. I acidify the soil twice a year at most. They were caught blooming while we were hit by the February 16, 2021 Freeze (-2F temperatures). All plants lost foliage and some branches but they either leafed out, grew new stems or both. They even bloomed late in the season in 2021. With caliche and limestone soils, you may have to grow them in raised beds (periodically acidify them) or in pots with an ericaceous, well draining, potting mix. Their root system is very shallow, about 4" deep and pancake shaped so you do not need to build excessively high raised beds. You just need to apply the acidifying roduct regular per product directions and test the soil often to see that all is well. They tend to tolerate slightly alaline soil levels (less than 7.6) in my organic matter rich garden.

Thanks to you all so far. What products do you use to acidify the soil. I think I'm leaning toward keeping the plants in pots; however, the water here is also high pH, so even a neutral soil will become high pH after some watering.

Thanks GG. Vinegar in the water is something I should have thought of.

For soil I was going to mix coco coir, compost, and perlite at equal parts. Do you have thoughts on that?

For a container? Not ideal but it can work. The compost will degrade quickly and you will need to repot next season.

I'd prefer to replace the compost with bark fines and at a 3:1 ratio (3 parts bark to one part each perlite and coir). Not only does bark hold up well, is reasonably moisture retentive but it will also provide the degree of acidity the azaleas prefer.

Thanks. I'm going to our local materials supplier today or tomorrow. Haven't been there since moving back to SA, and I need to see what's changed in 10 years.

Just an FYI, but bark fines are sometimes sold as 'soil conditioner'.

Good to know.

I grow mine in huge pots, easier to keep soil acidic & for me to move to part shade.

I have 4 Encore® 'Autumn Embers' along a rear driveway going into year 3 I think. Mine took a terrible hit in the snow/ice storm of Feb 2021. Actually had 5 and lost 1 to the freeze. Mine get water on auto-sprinkler mister every 3 days. They are in dappled shade. I fight the alkaline soil in Temple for sure. When I fertilize regularly with acid-lover fertilizer, they do better. When I get lazy or health issues get in the way of gardening, they get a little puny. I want to get my hands on some pine needles to spread around them but having no luck there to date. Here's what they look like currently:

Not really getting to be big bushes, but in the narrow 2' wedge of soil by that driveway they live in, probably just as well they not get too big.

Blooming in 2019.

EDIT: I give up. Can't seem to upload either picture today for you. It uploads but then vanishes when I hit submit.

Pine needles, aka pine straw, is a great mulch in areas where available. However there is a misconception that it will help to lower soil pH. It won't. Living pine needles are slightly acidic. But by the time they dry and fall they have lost most of their acidity and are close to a neutral pH. Even if they were still highly acidic, it would take truckloads of them to have any appreciable effect on soil pH.

I concur with gardengal48. Another myth: sprinkle coffee grounds to acidify the soil.

I do occasionally use coffee grounds, as well as acid-lover fertiilizer twice a year.