It's important to keep the dreaded black mold off your Hummingbird Feeders. Dirty feeders can cause illness and death in hummingbirds. You should replace your nectar every few days in hot weather and be sure to thoroughly rinse out the bottle each time. Try to avoid using soap whenever you can.
This is important. If you don't keep your feeder clean, your hummingbirds will not visit them.Every filling, flush the feeder with hot tap water (not distilled); a bottle brush can be very helpful. Avoid soap whenever possible as hummingbirds can apparently taste soap/detergent residue, and they don't like it. If the sugar solution in your feeder turns cloudy, it's spoiled and needs to be replaced. When the temperature is over 80 degrees (F), clean and refill every three or four days. Over 90°F, it might spoil in two days.
If mold does appear and you need a more thorough cleaning method, here are some tips on how to clean those hard to reach places on a hummingbird feeder. At least once a month, clean the feeder thoroughly with a solution of 1/4 cup bleach to one gallon of water. Soak the feeder in this solution for one hour, then clean with a bottle brush. Rinse well with running water and refill. Any remaining traces of bleach will be neutralized by reacting with the fresh syrup, and there's no need to air dry before refilling. Bleach is both safe and very effective.
Vinegar is a good alternative to dish soap too as it has sterilizing qualities. Fill the bottle up with 2 parts water to 1 part vinegar and let it soak for several hours. Be sure to rinse thoroughly before refilling with nectar. You may still need to use a stiff brush to clean the base and also a bottle brush for the bottle.
If you don't want to use bleach or vinegar and you don't have a bottle brush, this is a good method for cleaning your feeder without a brush. Many people warn against using soap to clean out a hummingbird feeder because even the smallest residue tastes bad to hummingbirds. However, the job may really require it and as long as the bottle is thoroughly rinsed afterwards, it should be OK. However, sometimes, even a bottle brush and soap can't reach around the thin neck of the bottle and the following is a good method for cleaning the inside of the bottle without a brush.