Good day to you! I noticed in a recent play that the farmer chose to clear the field of rotten plants (silkweeds, in this case) while other plants were still harvestable, but rotting as she worked. I think she just went for whatever was closest to her. Obviously, this meant the actual harvest was smaller. I think she should prefer to retrieve harvestable plants first, then deal with any rotten plants, as there is less of a time pressure for removing rotten plants.
As a sidenote, even plants she was busy gathering continued to rot, which is a bit of a strange thing to witness. They still counted as properly gathered plants, but even so.
11:15 and then some.