Plants beginning to cause rash (6)
I believe the answer is:
chives
'plants beginning' is the definition.
'chives' can be an answer for 'plants' (I've seen this before). I am not sure about the 'beginning' bit.
'cause rash' is the wordplay.
'cause' becomes 'c' (this might be a standard abbreviation which I don't know about).
'rash' becomes 'hives' (hives is a kind of rash).
'c'+'hives'='CHIVES'
'to' acts as a link.
Can you help me to learn more?
(Other definitions for chives that I've seen before include "Leaves used as onion-flavoured seasoning" , "Herb of the onion family" , "Herbs with long tubular onionflavoured leaves" , "Plant of onion family" , "Plants" .)