Trstenjak collaborated closely with the Slovene-Croatian poet and ethnologist Stanko Vraz. Influenced by the theories of Ján Kollár and Pavel Jozef Šafárik, two influential [Slovak] philologists who advocated Pan-Slavic ideals, Trstenjak wrote several historical books, in which he claimed that the Slavs were the most ancient people in Europe (an antecedent of the Venetic theory). However, he gave up these claims after he found they were scientifically untenable.
National awakening work
During the Spring of Nations in 1848, Trstenjak became an enthusiast supporter of the United Slovenia program. As a close collaborator of Matija Majar, the author of the program, Trstenjak helped in raising signatures for the establishment of a unified political entity comprising all Slovenian ethnic territory. After 1849, he established contacts with Janez Bleiweis and Lovro Toman who became the leaders of the Slovene National Movement in the 1850s and early 1860s. In 1863, he was among the co-founders of the prestigious publishing house and scientific society Slovenska matica. He was also a collaborator of the bishop Anton Martin Slomšek. In 1877, upon his initiative, a marble plaque to Slomšek was unveiled on his birth house in Uniše.
Kdo so bili Ambidravi, in kdo je sozidal starodavni mesti Virunum in Teurnia Kelti ali Venedi? V Celovcu : J. Leon, 1853
Mesec Marije, ali častenje presvete device Marije skoz eden celi mesec s vsakdanjimi premišljevanji, molitvami in izgledi iz živlenja svetnikov, ter z molitvami v jutro, večer, pri sv. maši, za spoved ino sv. obhajilo, kak tudi s kratkim opisom naj imenitnejših Marijinih svetstev, katere slovenski romarji obiskavajo. U Gradcu: J. Sirolla, 1856
Pannonica: spomeniški listi. Samozal. D. Trstenjak, 1887
Weriand de Graz: zgodovinsko-rodoslovna razprava. V Celovci : pisatelj, 1884
Triglav, mythologično raziskavanje. Samozal. D. Trstenjak, 1870
Slovanščina v romanščini. [Ponikva]: pisatelj, 1878