Ways to get the ref's back up are growing, naturally (5)
I believe the answer is:
ferns
'ways' is the definition.
Although both the answer and definition are plural nouns, I cannot see how one could define the other.
'the ref's back up are growing naturally' is the wordplay.
'back' is a reversal indicator.
'up' says the letters should be written backwards (in down clue: letters go upwards).
'are growing naturally' becomes 'sn' (I can't explain this - if you can you should give a lot more credence to this answer).
'ref' backwards is 'fer'.
'sn' written backwards gives 'ns'.
'fer'+'ns'='FERNS'
'to get' is the link.
Can you help me to learn more?
(Other definitions for ferns that I've seen before include "Flowerless plants with feathery or leafy fronds" , "Frondy plants" , "Flowerless plants with feathery green leaves" , "Ancient plants" , "Plant, maidenhair or tree say" .)