Weed solution includes ammunition (9)
I believe the answer is:
groundsel
'weed' is the definition.
(I know that groundsel is a type of weed)
'solution includes ammunition' is the wordplay.
'solution' becomes 'gel' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'includes' means one lot of letters goes inside another.
'ammunition' becomes 'rounds' (I've seen this before).
'gel' going around 'rounds' is 'GROUNDSEL'.
Can you help me to learn more?
(Other definitions for groundsel that I've seen before include "Common weed" , "Plant of daisy family" , "feed to the birds" , "plant, unwanted?" .)