Eucalyptus in pot starts to reach amazing height (6)
I believe the answer is:
jarrah
'eucalyptus' is the definition.
(I've seen this before)
'pot starts to reach amazing height' is the wordplay.
'pot' becomes 'jar'.
'starts to' suggests taking the first letters.
The initial letters of 'reach amazing height' is 'rah'.
'jar'+'rah'='JARRAH'
'in' acts as a link.
(Other definitions for jarrah that I've seen before include "timber-tree" , "Eucalyptus" .)