Q.Why Are My False Indigo Baptisia Plant Leaves Turning Yellow
The plants are new this year. It has been very hot and dry the last few weeks. I have been watering them because of the dryness. They have mulch around them also. I don’t know how to send you a picture.

Certified GKH Gardening Expert
Unfortunately, without photos, I will only be able to take a few guesses at what could be the issue.
To me, this sounds like overwatering in compensation for heat. The soil should still dry out down to about 3 or 4 inches, thoroughly, between waterings to avoid rot.
If these were planted in the heat, then they are likely going to have a very hard time getting established. This will be best done in Fall and Spring.
https://www.gardeningknowhow.com/ornamental/flowers/baptisia/page/2