This rare kanji has no clear standalone meaning. Treat its meaning as uncertain.
The exact historical development of 枽 is uncertain. It may be a variant or simplified form, but its origin is not well established.
The kanji looks like a plant with 十 on top, a leafy middle 廿, and a tree 木 at the bottom, but its meaning is unclear.
For ソウ, imagine a sower planting a mysterious tree: sow -> ソウ, even though the kanji's meaning is uncertain.