Before joining:

Himmler left gymnasium (high school) to train as a Fahnenjunker (junior officer candidate) in the 11th Bavarian Infantry Regiment in 1918 (his father had applied to several Bavarian regiments on his behalf). But the War finished before he completed his training and he was discharged. He went back to school in Landshut to complete his Abitur (diploma) on a special course designed to help those who'd left school to complete their education quickly. He joined the Freikorps (a paramilitary anti-Communist group) and the Oberland Reserve Company, but he didn't see any active service and this Company was, too, disbanded without him gaining a regular commission.

With his dreams of military service over, he turned to agriculture. He was from a middle-class family, not a family of landed gentry or farmers, so this career choice may have been because he was attracted to the romantic ideal of the return to the soil. His reading lists show he was familiar with the kind of romantic anti-urban sentiments then current in Bavaria. He went to a farm in Ingolstadt and intended to work for a year as a kind of apprentice gaining practical experience before going to a Technical High School. But he was unused to farm work, had always been a sickly youth, and quickly fell ill. He spent a month in hospital and on his discharge was recommended to defer the practical work and go straight to academic study. So he moved to Munich and was enrolled in the Technical High School to study agronomy.

While in Munich he saw more quasi-military service with the 14th Alarm Company of the Protection Brigade during the 1920 uprisings, but the Allies forced the Protection Brigades to shut down: the Treaty of Versailles had placed strict limits on the German armed forces and these kinds of paramilitary bands were (rightly) seen as ways around those limits. Himmler joined the Einwohnerwehr (Residents' Defence Force) and various loyalist clubs. In 1921 after his year of study he did his year of practical work, on a farm at Fridolfing near the Austrian border, then it was back to Munich to complete his studies. In summer of 1922 he passed his exams and graduated with a diploma in agriculture, and took up a job with an agrochemical company called Stickstoff-Land GmbH in Schleissheim, a Munich suburb. He seems to have worked as a kind of technical analyst: suffice it to say this work was pretty far from the idealised dream of being a yeoman farmer he'd had.

By 1923 hyperinflation and civil unrest were taking off in Germany. Himmler joined yet more paramilitary/civil defence groups, including one called the Reichsflagge. By this time he was associated with Ernst Röhm. He followed Röhm into the Reichskriegsflagge (a different group!) and thereafter into the Nazi Party, joining as member number 42,404 in August of 1923.

In short, prior to joining the Nazi Party, Himmler had tried and failed to become a military officer, and then seen his romantic dreams of farming life meet the more prosaic reality of working for a fertiliser company.

Source: Peter Longerich, Heinrich Himmler: A Life (2011)