Plant dahlias at intervals around gazebo's base always (4,4)
I believe the answer is:
aloe vera
'plant' is the definition.
The answer is an example.
'dahlias at intervals around gazebo's base always' is the wordplay.
'at intervals' indicates alternate letters (letters are taken at regular intervals).
'around' indicates putting letters inside.
'base' indicates one should take the final letters (the base of the word).
'always' becomes 'ever' (synonyms).
The last letter of 'gazebo' is 'o'.
The alternating letters of 'dahlias' are 'ala'.
'o'+'ever'='oever'
'ala' enclosing 'oever' is 'ALOE VERA'.
(Other definitions for aloe vera that I've seen before include "type of juice" , "Cosmetic plant extract" , "Plant with juice used for treating burns" , "Plant juice used in cosmetics" , "Plant product used in some cosmetics" .)