Space base has small plants (6)
I believe the answer is:
embeds
'plants' is the definition.
(I know this)
'space base has small' is the wordplay.
'space' becomes 'em' (in typography, a space as wide as a letter 'm').
'base' becomes 'bed' (both can mean the bottom of something).
'has' means one lot of letters go next to another.
'small' becomes 's' (abbreviation - e.g. clothes size).
'em'+'bed'+'s'='EMBEDS'
(Other definitions for embeds that I've seen before include "Sets or fixes firmly and deeply" , "Fixes firmly into surrounding mass" , "Attaches to, as a journalist to a military unit to report a war" , "Fixes in something solid" .)