Plant container outside Four Seasons finally serves as turning point (6)

'serves as turning point' is the definition.
I can't tell whether this definition defines the answer.

'plant container outside four seasons finally' is the wordplay.
'plant container' becomes 'pot' (I've seen this before).
'outside' means one lot of letters goes inside another.
'four' becomes 'iv' (roman numeral).
'finally' suggests the final letters.
The final letter of 'seasons' is 's'.
'pot' enclosing 'iv' is 'pivot'.
'pivot'+'s'='PIVOTS'

Can you help me to learn more?