Insists on having a handful of soil? (5,4,6)

'insists on' is the definition.
I know nothing about this answer so I cannot tell whether this works.

'a handful of soil?' is the wordplay.
I cannot quite see how this works, but
'a' could be 'one' and 'one' is found in the answer.
'of' could be 'o' and 'o' is found in the answer.
'soil?' could be 'ground' ('ground' can be a synonym of 'soil') and 'ground' is found in the answer.
This explanation may well be incorrect...

'having' is the link.

Can you help me to learn more?