LeAnna,
I love the nature study aspect of CM, and we've had our kiddos keep a nature journal from the time they are in second grade on up. Each child has one (a blank bound journal) that he sketches things seen outside in nature. We assigned a nature journal entry once weekly on Fridays for years. Now, my boys add to their nature journals on their own. We do much more sketching in the journals in the summer. My oldest sons have each completely filled their nature journals.
Within your HOD guides, we do try to encourage kiddos to notice God's creation and to do journaling type exercises through our notebooking about nature. The assignments for the One Small Square books are great tools we use toward that end (doing the Seashore, Woods, Arctic Tundra, Cactus Desert, and Coral Reef). John Audubon and the Birds of the Air book focus on drawing, sketching, listening, and observing birds. The Land Animals book focuses on land animals and tracks. Find the Constellations, Along Came Galileo, and the Astronomy book focus on the night sky and the heavenly bodies. Plant Life in Field and Garden spends time sketching, labeling, and pondering various plants. Exploring Planet Earth focuses on earth science and includes much study in that area. So, there is quite a bit of focus on "nature" and appreciating God's creation within HOD already should you feel that you may not have time for an extra nature study option.
Blessings,
Carrie