Hello Kyla!
Yes,burials was made in the winter. The church could dig some graves in the fall, leave them open but covered with planks of wood. When someone died,the planks was removed, the coffin was placed in the grave and covered with planks again, until spring, and then covered properly with soil. Sometimes the church could store the coffin or dead person in the vapenhus, a kind of small annex. Some very remote areas used small islands (holme, ex. Gravholmen a common name of the island). Used by my finnish ancestors, and a custom also used by the native Swedes sapmis.This custom might also be partly supersticios, the soul of the dead person cannot travel over water. And in the spring, the coffin was brought down to the church and the graveyard. In the county of Värmland and in the finnish parishes (where my ancesters comes from), I also discovered that the very remote finnish farms used some kind of unsacred halfway graveyard, where they buried or left the dead until the next trip to the church. In the early 1700th hundreds, my ancestors in Värmland, parish Dalby, was forbidden by the preast to bury their dead in their own yard .
Regards,
Antoinette