Greens periodically seen around desert region (5)
I believe the answer is:
negev
'desert region' is the definition.
(I've seen this before)
'greens periodically seen around' is the wordplay.
'greens' becomes 'veg' (greens can informally mean vegetables).
'periodically' indicates alternate letters (letters must be selected 'every so often').
'around' is a reversal indicator.
The alternate letters of 'seen' are 'en'.
'veg'+'en'='vegen'
'vegen' written backwards gives 'NEGEV'.
(Other definitions for negev that I've seen before include "Semi-desert area" , "Desert region in Israel" , "Israeli desert area abutting Sinai" , "Wilderness" , "Southern Israeli desert" .)