Planted around wild vale on English river by Spartacus's boss

'spartacus's boss' is the definition.
I don't know anything about this answer so I cannot tell whether this works.

'planted around wild vale on english river' is the wordplay.
'planted' becomes 'sown' ('sown' can be similar in meaning to 'planted').
'around' indicates putting letters inside.
'wild' indicates an anagram.
'on english river' becomes 'er' (I am not sure about this - if you are sure you should believe this answer much more).
'vale' anagrammed gives 'lave'.
'sown' placed around 'lave' is 'slaveown'.
'slaveown'+'er'='SLAVE-OWNER'

'by' is the link.

Can you help me to learn more?