Having pulled out very stupidly overtake heavy plant (3,4)
I believe the answer is:
oak tree
'having pulled out very stupidly overtake' is the definition.
I know nothing about this answer so I can't judge whether this works.
'heavy plant' is the wordplay.
'heavy' becomes 'oak' (I can't explain this - if you can you should give a lot more credence to this answer).
'plant' becomes 'tree'.
'oak'+'tree'='OAK-TREE'
Can you help me to learn more?
(Other definitions for oak tree that I've seen before include "Matured acorn" , "famous royal hideout" , "Product of acorn" , "Old plant (round which to tie a yellow ribbon?)" , "Source of acorns" .)