So my care is to propagate a tree (8)
I believe the answer is:
'a tree' is the definition.
(sycamore is a kind of tree)
'so my care is to propagate' is the wordplay.
'is to propagate' indicates an anagram (reordered letters generate or propagate the answer).
'somycare' anagrammed gives 'SYCAMORE'.
(Other definitions for sycamore that I've seen before include "Tree, form of maple", "Large maple", "Tree with winged seeds", "Tree for the odd Rose Macy", "Tree - may score (anag)".)