Want a natural way to keep pesky flies out of the kitchen? Common sense first: Cover all food and keep whatever you can in airtight containers or in the refrigerator. Second: Keep a small pine-tree plant in the kitchen. Of all the natural oils and scents that deter flies, pine oil is the most effective and the strongest. By keeping a living tree in the kitchen, you'll keep flies away and have something beautiful, too. You can find easy-to-care-for varieties at any home improvement store.