But again, my neighbor unwittingly, accidentally grew them in a semi-shady, sloping, entirely unattended rock garden beneath her deck. Full TX sun is quite different from full sun elsewhere, maybe that's where I'm going wrong.
Once they go to seed you never get rid of them for example my compost piles
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.