Big Bend National Park is one of my favorite places on the planet. My photography guide to Big Bend is here. March and April are good months to go. You will see more flowers in mid to late April but it will also be hotter. Fall is a prime time also. If you don’t mind the chance of a sudden cold spell and maybe some snow, I like winter in Big Bend too, but most people prefer spring and fall. Summer is ungodly hot.
The 10 Adventures web site has An Extensive Guide to Big Bend National Park that is worth your while. Check it out at the link below.
An Extensive Guide to Big Bend National Park at 10 Adventures
Photography in Big Bend National Park at JimDoty.com
Big Bend National Park – official NPS site