Male digger's first tool for plant (8)
I believe the answer is:
mandrake
'plant' is the definition.
(I know that mandrake is a type of poisonous plant)
'male digger's first tool' is the wordplay.
'male' becomes 'man' (man is a kind of male).
'digger's first' becomes 'd' (1st letter of 'digger').
'tool' becomes 'rake' (rake is a kind of tool).
'man'+'d'+'rake'='MANDRAKE'
'for' is the link.
(Other definitions for mandrake that I've seen before include "Exotic plant" , "Plant once believed to shriek when pulled up" , "Poisonous plant once thought to have magical powers" , "Plant with forked root used in magic" , "May apple" .)