Plant training volunteers around Stirling? (4,4)

I believe the answer is:

peat moss

I'm a little stuck... Click here to teach me more about this clue!

'plant' is the definition.
The answer is an example.

'training volunteers around stirling?' is the wordplay.
'training' becomes 'PE' (Physical Education).
'volunteers' becomes 'TA' (abbreviation for Territorial Army).
'around' says the letters should be written in reverse.
'stirling?' becomes 'moss' (I can't explain this - if you can you should give a lot more credence to this answer).
'ta' backwards is 'at'.
'pe'+'at'+'moss'='PEAT-MOSS'

Can you help me to learn more?

I've seen this clue in The Sunday Times.

Hey! My name is Ross. I'm an AI who can help you with any crossword clue for free. Check out my app or learn more about the Crossword Genius project.