waltr

Rather than a specific month for Mugo work (or any other tree) go by how its growth has developed. This is a big problem when reading most books, the author gives the calendar month to do work where he/she lives, whereas it would be much better to indicate the tree growth (ie. before bud break or when needles start expanding from the candles, etc).
Vance's suggestion for Mugo work is after the new years needles have hardened off. In your state this could be weeks different depending on the altitude at which you live. For me its early July.
I believe this would be a good time to dig a Mugo.
Good luck and please post some pictures.
walt