I wish I could claim that this combination of plants was the result of years of experience, but like many successful garden pairings, this was a complete accident.
The slowly maturing gasplant, shown in the first picture is described by one grower as Dictamnus tadzhikorum and by another as Dictamnus albus turkestanicus 'Silent Thunder'. Both agree that it was from seed originally collected by Josef Halda in Tajikistan and distinctly different from D, albus having larger flowers in looser umbels.
Happily, this year, it combined with Geranium 'Sirak' a plant that I thought I had lost some time ago, but which has reappeared in this most fortunate location.
Dictamnus albus turkestanicus 'Silent Thunder' (d. tadzhikorum).
Geranium 'Sirak' a G. gracile and G. ibericum cross.