Most luck I ever had with nasturtiums was when we lived in Prince Albert, Saskatchewan. I have problems here in western Oregon...they don’t like full sun and seem to do best in Fall...must like cool nights, AFTER they start flowering.
My neighbor who grew them unknowingly also has diverted her greywater to drain in her 1/2 sun hillside rock garden. When I scrambled down to inspect the plants, they were dangling by long roots that grew under large limestone rocks. I went and inspected the slope again today to see if any others had volunteered, not yet.
I also have a large rock garden, 1/2 shade, and another neighbor last year took out 2 large branches overhead, thinking he was being helpful - the rock garden ends at the road - and fried all the shade plants I’d coaxed to life in this desert climate of Centex.
Couldn’t dress him down, he honestly thought he was helping.