harvesting mullein flowers

Hi there. I have some mullein growing in my yard this year and i would like to make a mullein flower oil out of them. Do i need to pick the flowers when they are in bloom or just before they open up? or does it matter? And i have heard that you should only take the first years leaves. Is that true? or are second year leave ok to pick?

Thanks!

Edit: And do i have to pick each individual flower? or can i just cut off the whole top and put olive oil over it? Tweet