A melon requires heat and moisture (6)
I believe the answer is:
sundew
'a melon' is the definition.
The definition and answer can be both plants as well as being singular nouns.
Maybe they are linked in a way I don't understand?
'heat and moisture' is the wordplay.
'heat' becomes 'sun' (I can't justify this - if you can you should give a lot more credence to this answer).
'and' means one lot of letters go next to another.
'moisture' becomes 'dew' (I've seen this in another clue).
'sun'+'dew'='SUNDEW'
'requires' acts as a link.
Can you help me to learn more?
(Other definitions for sundew that I've seen before include "Insectivorous plant" , "Insects" , "Insect-eating bog plant" , "Carnivorous plant" .)