Think highly of, these days, swampy ground (6)
I believe the answer is:
admire
'think highly of' is the definition.
(admiring is a kind of thinking highly of)
'these days swampy ground' is the wordplay.
'these days' becomes 'ad' (as in Anno Domini, after Christ).
'swampy ground' becomes 'mire' (I've seen this before).
'ad'+'mire'='ADMIRE'
(Other definitions for admire that I've seen before include "Think highly of, esteem" , "Respect greatly" , "Fall for" , "Dig" , "Idolise" .)