Penstemon roots don't like constantly moist soil. Did you check soil moisture levels before watering? A finger stuck down an inch or so in the soil should tell you a lot. Is the plant new (not yet established)? If that's the case, the rootball may be drying out before the surrounding soil, especially if the rootball is potting soil/ground bark/etc and it's planted in average soil.

Thanks Brandon. It was planted last spring. I will try to get a better indication of the moisture level around the root ball. I may need to move it.

Unfortunately I lost the red Beardtongue. I think you are right that the root ball was not absorbing water. I now have another similar situation with an annual in a large pot with an angel trumpet. While the soil in the pot is moist, the root ball of the annual is dry. Do I keep watering the annual more frequently and try not to let the Angel Trumpet get too much water? Would it help if I dug up the annual and loosened up the root ball?

You could try either or both. Annuals are usually pretty tolerant of root disturbance, so when I plant them, I get rid of all excess potting soil (where there are not roots yet), cut or loosen up any pot-bound roots, and make sure there is good contact between the annuals root system and the surrounding soil. Pots can definitely complicate drainage, and different soil types in a pot can really be a challenge.

Thanks, I'll give it a shot.