Making topiaries

Yesterday I was at Target and I saw these rosemary plants and I thought they would be perfect to make little topiaries. This is a project I have wanted to try for a long time. I want the pots to get mossy which is not always easy when you live in a dry climate. I've heard if you brush plain yogurt or buttermilk on the pot and then rub moss on it that it will grow moss quicker. I'm not sure how