KNOW YOUR ONIONS

To know a lot about a particular subject. 

know onions

Saberlo todo de un tema

PUT THE ROSES IN CHEEKS

To make someone look healthy

put the roses in cheeks

Tener buena cara

PUT THE BITE ON SOMEONE

To try to get money from someone.  Also to put the touch on someone.

put the bite on
Intentar sacarle dinero a alguien

HAVE GREEN FINGERS

To be good at keeping plants healthy and making them grow.

(In America, people say Have a green thumb)

have green fingers
Tener mano con la jardinería