Containing meagre energy, lacking top-grade vegetation (8)
I believe the answer is:
greenery
'vegetation' is the definition.
(I've seen this before)
I cannot understand how the remainder of the clue works.
Can you help me to learn more?
(Other definitions for greenery that I've seen before include "Decorative boughs" , "Foliage etc" , "Verdure" , "Leaves etc" , "Colourful display" .)