A pot initially concealed garden pest (5)
I believe the answer is:
aphid
'garden pest' is the definition.
(I've seen this before)
'a pot initially concealed' is the wordplay.
'initially' says to take the initial letters.
'concealed' becomes 'hid' ('hide' can be a synonym of 'conceal').
The first letter of 'pot' is 'p'.
'a'+'p'+'hid'='APHID'
(Other definitions for aphid that I've seen before include "Garden bug" , "Insect feeding on plant juices" , "Small plant-sucking insect" , "Small insect like greenfly" , "Greenfly etc" .)