This rare kanji has no clear standalone meaning. Treat its meaning as uncertain.
鉎 combines 金 (metal) with 生, which likely contributes the sound. The exact historical development is uncertain.
The kanji has metal 金 and life/birth 生, but its meaning is unclear. It might relate to rust (さび), so picture metal 金 that has been 'born' 生 into rust.
For ソウ, imagine a piece of metal 金 that is so rusty it looks like it's been buried in the soil (ソウ sounds like 'sow' as in planting). The rust is like something growing from the metal.