let it grow

Let it grow refers to when a guy plants the seed in a conversation with a lass,

The idea is planted into the lasses head which will grow with the right amount of water to the outcome the guy is wanting.

Lass: Asif Only thnk ive seen u once lol xx
Guy: Init same when u gt off bus I think, well avto change that 😉 xx
Lass:how u gna change that eh? Xx
... The seed is planted.
Now 'Let it grow'