I got this idea for natural air fresheners from this pin from Monica at The Yummy Life. She has whole list of recipes for different scents. She even says you can store them in jars in your refrigerator for up to two weeks and she also gives different ways to warm them.
I love this idea of making your own air fresheners because it's all natural, easy, and inexpensive. I also like that it makes your house smell nice, but it's not overpowering.
I've made a similar air freshener before which was nice for winter because it had apples, oranges, cloves and cinnamon. This one is great for summer because the lemon, vanilla, and rosemary smell so fresh and clean and perfect for summer. Just mix two cups of water, one teaspoon of vanilla, one sliced lemon, and three sprigs of fresh rosemary in a pan and simmer on the stove. If the water runs out, just add more.