This rare kanji has no clear standalone meaning. Treat its meaning as uncertain.
The exact historical development of 糚 is uncertain. It visually combines 米 (rice) with 莊, but the original semantic and phonetic roles are unclear.
With no clear meaning, picture 糚 as a mysterious container of rice (米) beside an ornate structure (莊), perhaps an ancient granary whose purpose is now forgotten.
For ソウ, imagine the sound of rice being poured into a container: 'sow' (ソウ) the grains into the granary.