In December 1362, Adolph IX married Anna of Mecklenburg-Schwerin (1343–1415), the daughter of Albert II, Duke of Mecklenburg.
The prince-archbishop of Bremen later failed to redeem the mortgage, and the Haseldorf Marsh has been part of Holstein ever since.
After his death, Count Nicholas of Holstein-Rendsburg and his nephews occupied Holstein-Kiel and Holstein-Plön.
The Counts of the Holstein-Pinneberg branch of the House of Schauenburg objected and demanded a share of the inheritance.
The dispute was settled amicably, with the counts in Pinneberg receiving monetary compensation, plus the district of Nienland (consisting of Neuland and the Lordship of Herzhorn) and some land along the Elbe.