Plant’s vitality (5)
I believe the answer is:
pulse
This clue is a double definition.
'plant's' is the first definition.
(as in a plant which produces pulses)
'vitality' is the second definition.
(I've seen this before)
(Other definitions for pulse that I've seen before include "Sign of life" , "Heart-throb" , "Heart rhythm" , "Musical rhythm" , "Edible seeds - which nurse may take" .)