New Date Communication

I am solo poly, relatively new to it. I’ve been seeing Birch for a few months. I went on a first date with Aspen, and plan to have a second date with them next week. I could see it potentially continuing. I told Birch ahead of time, and I told Aspen about Birch. I recently heard from Pine, who I had one date with a long time ago and we made plans for a second date in two days. I will tell Birch about the upcoming dates because that’s what we agreed on. Do I text Aspen about Pine before the date? Or tell him on our second date? What’s the protocol if you’re not in a relationship with someone and haven’t established any rules? I want to be transparent, but feel confused about the best approach.