Thorn at the start to be in red, red rose (7)
I believe the answer is:
towered
'red rose' is the definition.
'towered' can be an answer for 'rose' (I've seen this before). I am not certain of the 'red' bit.
'thorn at the start to be in red' is the wordplay.
'at the start' suggests taking the first letters.
'to' is a charade indicator (letters next to each other).
'be in' becomes 'owe' (owing is a kind of being. I am not sure about the 'in' bit.).
The initial letter of 'thorn' is 't'.
't'+'owe'+'red'='TOWERED'
Can you help me to learn more?
(Other definitions for towered that I've seen before include "Was taller and more eminent than others" , "rose" , "Was of great height, . . . . . . . over others" , "Loomed (over)" .)