Tillers are not hard to make from these trees (4)
I believe the answer is:
elms
'trees' is the definition.
(elm is a kind of tree)
'tillers are not hard' is the wordplay.
'tillers' becomes 'helms' (I've seen this in another clue).
'are not' suggests deleting specific letters.
'hard' becomes 'h' (abbreviation used in pencil classifications).
'helms' with 'h' taken away is 'ELMS'.
'to make from these' is the link.
I am not very happy about this link. Some or all of it may be part of another bit of the clue.
Can you help me to learn more?
(Other definitions for elms that I've seen before include "rugged feature of country churchyard" , "may have many leaves" , "Trees (of late, prone to disease)" , "Deciduous trees with rough serrated leaves" , "Trees sound like Cockney steering devices" .)