A simple nectar is made from four parts water and one part sugar. The solution needs to boil for two to three minutes to kill bacteria and then cooled before it's placed into feeders. Homemade nectar can last about two weeks when refrigerated.
The 4-to-1 ratio is similar to sugar concentrations found naturally in nectar that hummingbirds seek. Stronger sugar solutions may not necessarily hurt hummingbirds, but the nectar spoils more quickly. In summer, when hummingbirds rely less on nectar and more on insects as their nutritional needs change, thinner sugar ratios of 5-to-1 or even 6-to-1 are acceptable.
Since sugar solutions spoil rapidly in warm weather, keeping hummingbird feeders clean and free of mold, mildew and bacteria is critical. Scrub feeders weekly with warm water (no soap) and refill with fresh sugar water.