The grandson of Georg Dietloff, Friedrich Wilhelm, was also a significant figure for the von Arnim family and the governance of Boitzenburg. He was born on 31 December 1739, and at the young age of 24 took over his father's inheritance. He decided to enter public service. King Frederick II appointed him to the Privy Council of Justice and in 1768 made him director of the Uckermark High Court in Prenzlau. Of particular note was his love of and his keen sense for the beauty of the landscape. It is therefore also thanks to him that the castle and its park are so impressive. He moved all the farm buildings, such as the mill, smithy, brewery, distillery and granary from the castle island and had them rebuilt and expanded on the estate outside the castle district. The ring wall was torn down.
This created the conditions for a landscape park based on the English model while leaving part of the Baroque garden laid out by his grandparents to give the castle a worthy setting. Initially created according to a plan presumably drawn up by Jampers in 1780, the park was later extended by the famous landscape architect, Lenné, in 1838 during the time of his grandson Adolf Heinrich and redesigned to include the surrounding landscape. Friedrich Wilhelm also brought the larches to Boitzenburg. His first plantations (around 200 years old) still stand today as an avenue between the former Brüsenwalde district forester's office and the Mahlendorf head forester's office. He also continued the von Arnim tradition of supporting the local church and schools. His grandfather had already been very active in this field, supporting needy families by granting them exemption from school fees.