Plant food, when do they need it?

my plants are about a month old and r around a foot high (30cm) should i start to give them plant food it is organic so does it matter what time of there life i can give it to them?

Thanks guys and happy Tokin

 

Sorry im new to the game what does 1/4, is that a quarter?

 

the stuff i got are sticks so i just wacked a stick in a instructed, but thanks anyway.