coarse, harsh, rough, unpolished rice
糙 centers on a lack of refinement: something coarse, rough, or unpolished. The meaning extends naturally to unpolished rice as a specific example of a rough, unprocessed grain.
糙 combines 米 (rice) with 造, which likely contributes the sound and may suggest the idea of making or processing, pointing to rice that is still in a rough, unprocessed state.
The left side is rice 米, and the right side 造 suggests making or building. Picture rice that has just been made but not yet polished: it is still coarse and rough.
For ソウ, imagine a bowl of coarse, unpolished rice that you need to sow (ソウ) back into the field because it is too rough to eat. Sow -> ソウ.