Asking for permission to use the images to promotion.

Hi! :)
I am fairly new into the wedding photography business.
Something that i have been wondering about is, when do you ask your client for permission to use the images on your blog, website and so one or do you even ask?
So im currently setting up my new website and it hit me that i don't know if the clients know that im using there images on my new site.
Up to now i haven't really had a good web portfolio, so it hasn't really been a thing that i have been thinking about until now. So far i have had good experience with clients and they have loved my work. So i wondering what should i do in the present, should i just post them to build portfolio. And then i wondering how i could do this in the future, what is a good way to ask the client for permission to use the images for promotion.

So what are you guys doing?, are you asking them in the client meeting or are you sending them a message after the wedding and asking for permission to use the images?
I have heard of people who send out a survey on how there experience was and also asking them for permission to use the images on there webpage.

What are some of your experiences?