I have repeatidly tried to grow agastache here in TX and everytime they die. This year I tried cana, which is native and all 3 plants are gone. I put them into a raised bed that is fairly dry and still they didn't make it. I have 3 hybrids in a bed with fairly good dirt (2 are tuttifruitty and one is unknown) they are alive, but the unknown looks very sad. What am I doing wrong? These plants should do well for me and they don't. Last year I tried ruprestis and one of the short orange hybrids, none of which is with me now. Too much water perhaps? They just brown up and wither away.
What time of year are you planting them? TX summers can be pretty brutal, so if you're planting in the spring and weather gets too hot before they have a good chance to get established (or if you're planting them in the summer) that could be your problem. My weather isn't as consistently hot as yours is and I still have a pretty atrocious success record with spring planting. Fall/winter planting works out much better for me.
While A. cana is native to TX, it doesn't look like it's very widespread http://plants.usda.gov/java/county?state_name=Texas&statefips=48&symbol=AGCA So maybe your part of TX doesn't have the best conditions for it? I'd start by trying to learn a little bit more about the areas where it does occur in TX, and then think about how (if it's possible) to replicate those conditions in your yard. I know here in CA we have a ton of different native plant communities, and it's really helped me to understand what type of conditions each plant community occurs in because some communities can do well in a climate like mine but others can't. I don't know if TX has quite the variety of climates that CA does, but I'm sure there's still some variability.
Problems with spring planted ones I think can be explained by them not having time to get established before it gets hot (I've found drought tolerant plants can be the hardest kind of plants to get established with spring planting--once you get into summer it seems like it's almost impossible to water them properly. Too little and they don't do well because they're not established, but too much and they easily die). But if the climate/soil/etc in your part of TX are conducive to growing them then I would have expected you to have more success with the fall planted ones.
The other thing that might help is trying to provide a little extra shade for them their first year (while being really careful not to water them too much), that might help get them through that tricky first year where they need a little extra but it's really easy to overwater them too.
For the fall planted ones, I wonder if you're potentially being too nice to them the following summer. In nature they would get by with no supplemental water once they're established. In their first year they'd need a bit more, but maybe you could be giving them a bit too much. For perspective--High Country Gardens website lists A. cana as being good for areas with 10-20 or 20-30 in of annual rainfall, and 30-40 in (with care). "With care" to me means perfect drainage and no supplemental water once established. I looked up annual rainfall for Arlington and you're at 29 inches which is pretty close to that "with care" zone, and that suggests to me that if your conditions are at all sub-optimal (poorer drainage or a little too much supplemental watering) they could have trouble. Or if for whatever reason they didn't get adequately established over the winter, they could have problems the following year.
I do suspect over watering but I am not at all certain how you would keep any plant alive when temps are over a hundred for months on end with little night time cooling. I grow other drought tolerant natives with no trouble. The area they were all in has sandy soil and is a thin raised bed that gets over 6 hours of sun and seems to dry fast. I think this is the last year to try Agastache for me.
Most of the Section Brittonastrum agastaches are found in the SW USA and NW Mexico, mostly at higher elevations where they can benefit from the monsoon season. They will do well in arid environments, but can't handle hot, humid nights, which is why I had to largely abandon them in central North Carolina.
Good drainage (sand, with some grit, like expanded shale or slate pellets) and some organic compost will help. I have started using a commercial soil mix with composted peanut hulls, and have had good results. The second feature affecting longevity is the level of soluble fertilizer. Depending on native conditions, too much NPK when young will make for weak plants later. This is true for alpine rock garden plants.
As far as the market named forms, these have such a mixed parentage that general advice is advised. Throwing a bunch of different ones into your climate and observing which volunteers come back is a good way to select for forms that will work well for you. High Country Gardens is at the southern end of the Front Range of the Rockies, where Agastaches naturally do well.
When I owned a home in Greensboro, I got no viable volunteers. Agastaches can be easily hand-pollinated.
Your point about finding out where these species grow would be especially valuable if the collection data has information on the soil type and plant associations.