A floral artist from Warren transformed the front of the United States Post Office into a holiday wonder this week, using flowers that would otherwise have been thrown out to spread color and beauty around the front of the Child Street building. Danielle Moore, owner of Wren Floral Design, purchases much of her stock from the Floral Reserve in Providence and recently got involved in its “Reserve Renegade” program, which gives floral designers last week’s flowers to use for “pop-up” art installations in their town. Ms. Moore, who opened Wren earlier this year, does floral design for weddings, other big occasions and designed a backdrop for the Warren Folks Fest last August. This was the first such pop-up installation in Warren, and Ms. Moore said she chose the post office “because you know, holidays!”