Botanical garden (9)
I believe the answer is:
arboretum
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">botanical garden</span>' is the definition.<br/ ><span class="explanation-format__explanation">(synonyms)</span><br/ ><br/ >This is the entire clue.<br/ ></span>
(Other definitions for arboretum that I've seen before include "Botanic garden of trees" , "Botanical garden of trees" , "Tree display centre" , "Botanical tree garden" , "Place for cultivation of trees" .)