Remove white papery skin from garlic head; separate but do not peel cloves.
Place garlic, olive oil, potatoes, thyme sprigs, and rosemary sprigs in a large bowl; toss to coat. Arrange potato mixture on a foil-lined jelly-roll pan.
Sprinkle evenly with 1/4 teaspoon kosher salt and pepper.
Bake at 450 for 25 minutes, stirring after 13 minutes.
Sprinkle with 1/8 teaspoon kosher salt and parsley.