If you want to be sure of daisies it's probably best to buy seeds (Yes you can do that ) cut your lawn , take a rake to it in patches and scratch hard so some of the grass comes away and you have some bare patches , scatter the seed and water . As another comment said , don't feed your lawn if you want wild flowers , I have lots of daisies , clover and dandelions in my lawn , it's never been fed and I always leave a few patches to grow while i'm mowing .