Delay supplying tree — new date needed for planting (4,4)
I believe the answer is:
lead time
'delay' is the definition.
(I've seen this before)
'tree new date needed for planting' is the wordplay.
'tree' becomes 'lime tree' (type of tree).
'new' is an anagram indicator.
'needed for planting' indicates putting letters inside (inserted letters get planted inside).
'date' with letters rearranged gives 'eadt'.
'lime' enclosing 'eadt' is 'LEAD TIME'.
'supplying' acts as a link.
(Other definitions for lead time that I've seen before include "What will American magazine editor do" , "Wait for delivery" , "I'm elated over advance period before start" , "period of preparation" , "How long to prepare" .)