In an example embodiment, a doser assembly includes a hopper assembly configured to receive plant material, a bracket assembly connected to the hopper assembly, and a roller in a hopper opening defined by the hopper assembly extending through the hopper assembly. An interior surface of the hopper assembly may define the hopper opening. The bracket assembly may include a shaft extending across a portion of the hopper opening. The roller may be in the portion of the hopper opening of the hopper assembly and may extend between a first part and a second part of the interior surface of the hopper assembly. The roller may be connected to the shaft and may be configured to rotate with rotation of the shaft.