Green garlic, which greatly resembles an overgrown scallion, has a mild flavor. Heads of fresh garlic are mature but just harvested. Because they haven't been cured for winter storage, they're very juicy. If you can't find either type of garlic, substitute scallions for the green garlic and regular (cured) garlic for the fresh. The soup will still be delicious.
Is this soup supposed to be chilled? There is nothing in the title or description that says so, but it didn't seem right heated up, probably because of the yogurt. I ended up throwing it out because I don't care for chilled soup, but others might like it. If a soup is supposed to be chilled it really should say so right up front, because that's definitely not for everyone, and it's a shame to waste beautiful organic ingredients.