Here's my reciepe
1 bulb crushed dropped into 1 litre of water, boil for 5 mins, and strain into a bottle.
To use, add 1 Tablespoon per litre of water and spray.
I guess I sprayed monthly ish?????
They smell was a bit garlicky while spraying, but in didn't notice it at all afterwards, but then I have an awful sense of smell.
Actually thinking about it, I didn't have problems with caterpillars either, monarchs included...