Plaster crops up on bed almost (6)
I believe the answer is:
stucco
'plaster' is the definition.
(I know that plaster can be written as stucco)
'crops up on bed almost' is the wordplay.
'crops' becomes 'cuts' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'up' is a reversal indicator (in down clue: letters go upwards).
'on' means one lot of letters go next to another.
'bed' becomes 'cot' (cot is a kind of bed).
'almost' means to remove the last letter (most of the word but not all of it).
'cuts' back-to-front is 'stuc'.
'cot' with its final letter removed is 'co'.
'stuc'+'co'='STUCCO'
Can you help me to learn more?
(Other definitions for stucco that I've seen before include "White plaster covering for exterior walls" , "Fine plaster used on wall surfaces" , "material for covering wall" , "Fine plaster for ornamenting walls etc" , "Plaster used for moulding and decorating" .)