Campanula portenschlagiana is an ornamental plant originally from the Dalmatian Mountains in Croatia. Like many potted flowering plants, C. portenschlagiana is vegetatively propagated from mother plants shoot explants. In C. portenschlagiana explants, adventitious root formation success depends on the genetic background, where rooting ability can be classified in a range from easy-to-root to difficult-to-root genotypes. In this study, we worked with two different genotypes of C. portenschlagiana, 'Deep Blue Ocean' and 'White Ocean'. The explants were grown in an aeroponic system for 21 days, where the base of the shoot explants was irrigated with nutrient solution (control), nutrient solution and 1 mM of L-glutamate, or nutrient solution and 1 mM of L-tryptophan. We found different root abilities between the two genotypes, and the 'Deep Blue Ocean' had a higher percentage of rooted explants (100%) when compared with the 'White Ocean' (25%). In the 'White Ocean', L-Glutamate and L-tryptophan treatments increased the percentage of rooted explants to 90% and 50%, respectively. L-glutamate and L-tryptophan treatments increased biomass of root and shoot in the 'Deep Blue Ocean'. In the 'White Ocean', L-glutamate treatment increased biomass of shoot but did not change the biomass of root. Taken together, our results showed that the amino acids L-glutamate and L-tryptophan play an important role in adventitious root formation in C. portenschlagiana, and it can help difficult-to-root genotypes to increase the success of rooting.