Cutting temperatures toughens tree out in conservatory (10)
I believe the answer is:
greenhouse
'conservatory' is the definition.
(thesaurus)
I don't understand how the remainder of the clue works.
Can you help me to learn more?
(Other definitions for greenhouse that I've seen before include "see-through construction" , "A place for growing" , "Glass building for rearing plants" , "Horticulturalists' glass building" , "somewhere hot" .)