Rather than remain in the military, Aamisepp chose instead to return to Estonia to study horticulture; he soon developed a hobby of growing potatoes, which he cultivated near his family's home. He experimented on the Imperator variety of potato, eventually leading to him developing his own variety. Dubbed the "Kalevipoeg", the new potato variety yielded a crop 58% larger than the Imperator. When the First World War broke out in 1914, Aamisepp rejoined the Imperial Army and was commissioned as an artillery officer. When the October Revolution resulted in the collapse of the Russian state, Amisepp joined the burgeoning Estonian Independence movement, helping to organize new army units.