I wish I could give you a good answer on this. The only reason I'm offering something is because you haven't gotten an answer yet.
I remember reading in one of the articles on this site that Howard actually uses garlic powder. I can't think of any reason why you would use more minced than powdered.
That said, I plan to use powdered at some point in the future. I assume that garlic will work the same way citronella plants, or any other plant oil works. The strong scent masks the human smell and mosquitos simply can't find you (and, hence, don't bite you).
What I will probably end up doing is using one of my little shakers of garlic powder from the kitchen, sprinkle it around our patio and just see how it works.
Maybe somebody else will post a reply who has actually used it.
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God speed!
Cara
**
Take time to stop and smell the flowers!
(or... as my ladybug refrigerator magnet says
"take time to stop and
eat the flowers!"
)