 You need to pay attention to the shelf life. Homemade hummingbird food in the refrigerator, you can keep it for up to two weeks. If you don't use it all by this time, just toss it. Nectar in the feeder itself should be tossed after two to four days, and that's really dependent on how warm the weather is. The feeder should be cleaned and refilled with a fresh batch of food. If there's any doubt as to whether that solution has spoiled, you want to err on the side of caution and just discard it.