The surname Harmse is derived from Harms or Harm, a Low-German / Niederdeutsch surname or name. In Plattdeutsch/Low Saxon the word sine is used as a possessive construction, hence Harmse indicates that it is the child of Harms, Harm, or Harmensze. The surname is also known to be a variation of Harmsen which is a farmer`s surname.
The surname is typically associated with low-altitude Northern Germany (e.g. Schleswig-Holstein), and the North-Eastern Netherlands (Gelderland province) where Niederdeutsch and related dialects may be found. One such dialect, Westphalian is spoken in Nordrhein-Westfalen, Germany.
The surname and variations of it such as Harms is also recorded in South-Africa due to Dutch colonization causing an influx of North-Germanic people. Many Germans, especially those from Northern Germany, would have found Old Dutch at the time (later developed into Afrikaans which is a modern Germanic language) very similar to their home language of Low German (Plattdüütsch, Nedderdüütsch), so there was little reason to form a sub-group within the then Dutch majority.
For more see: * Harmsdorf, a town in the Northern-Germany. * Old High German word harm meaning injury, Old Norse word harmr meaning grief * Plattdeutsch and dialects * Jan Strunk, 2004. Possesive constructions in modern Low Saxon