Am not sure if helpful, or if this would be somewhere you could visit for reference.

The Alnwick Victorian poison garden is fascinating and perhaps even has ideas for you.

https://www.alnwickgarden.com/the-garden/poison-garden/

https://en.m.wikipedia.org/wiki/Alnwick_Garden

Hope this helps. Am hoping to get to visit one day.

I found this article interesting on Caldera systems…

https://www.usgs.gov/news/caldera-systems-a-worldwide-family-more-just-yellowstone