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How to prevent moldy syrup in bee feeders

A reader asked this question yesterday and I thought it was worth writing about. Sugar syrup will mold very quickly, especially in the physical conditions of the hive. A white, fluffy growth may be seen in just a few days. A small amount of mold doesn’t seem to bother the bees, but if it gets thick and smelly the syrup should be discarded.

Beekeepers have come up with many methods to combat mold in syrup. One of my favorites is the baggie feeder because it severely limits the amount of syrup exposed to the air, and since the bees drink only from the slits in the bag, the syrup in those areas is quickly consumed.

Honey-B-Healthy contains essential oils which inhibit mold growth. This commercial product is effective because the emulsifier allows the oils to be blended into the syrup. Simply adding essential oils to syrup doesn’t work because the oil floats to the surface and accumulates in puddles, much like an oil spill in the ocean.

If you want to try making your own emulsion, the following recipe is used by some beekeepers for spring syrup:

    • Heat 5 quarts (5 l) of water to nearly boiling and then add ½ teaspoon (2.5 ml) lecithin granules. (Lecithin is the emulsifier.)
    • Stir until the lecithin is dissolved. (This may take a while; it tends to float.)
    • Once the lecithin is dissolved, remove the water from the heat and add 10 pounds (4.5 kg) of granulated white sugar. Stir until dissolved.
    • Add 1 teaspoon (5 ml) essential oil and stir thoroughly.

Lemongrass oil is reputed to have strong antifungal action. You can also use a combination of half lemongrass oil and half spearmint oil.

Other beekeepers prefer to use distilled apple cider vinegar or lemon juice. Both of these decrease the pH (increase the acidity) of the syrup. Honey is relatively acidic with a pH range of about 3.2 to 4.5 so bees tolerate the increased acidity very well while most molds do not. I have not tried this method, but I’ve read that 2 to 4 tablespoons/gallon of syrup is commonly used. Since the pH of water varies tremendously to start with, it is impossible to guess how much will be needed for any one water supply. If I were to try this method, I would start with the lesser amount and see how that worked.

Cream of tartar (related to tartaric acid but not the same) is sometimes used to increase acidity, but most beekeepers today stay away from it because of reports that it can cause bee dysentery.

All these methods can work to slow mold accumulation but none of them will stop it completely. If you have consistent mold problems, you may have to feed less syrup at each feeding so it is used up quickly.



  • put clorox in your bee feed ration 500/1
    I put 5 taplespoons per 5 gallons of feed
    This stops mold in the feed

  • Rusty, thank you for the recipe. Is this a concentrate like HBH? Or would more essential oil be required to make it a concentrate?

    • Jim,

      This is not thick like HBH. I got this recipe from another source, and they use the same amount per gallon of syrup as you would with HBH. It bothers me because I would like it thicker but I think that would require more lecithin and I don’t know how much of that is safe for bees. Using this recipe has worked for me, but I think it could be improved on.

  • I am getting red mold inside my plastic hive-top feeder jars – a couple of fuzzy red spots. And the inside of the lids and the threads of the caps are pink/red – not fuzzy but look as if stained by Koolaid.

    My bees were sealing the feeder lids into the hives with propolis and I was unable to pry them out so when I finally got them, I coated the outside (sides only, not surface where bees cling) of the caps with Vaseline. Could this be a problem? I don’t know what else to do. And that red stuff is scaring me.

    • Chloie,

      I’ve never seen red mold in a feeder (although I’ve seen some in my refrigerator) but most molds are harmless to the bees. The next time you change the syrup, try adding a teaspoon or so of vinegar to the jar. The vinegar makes the syrup more acidic which often suppresses mold growth, and since honey is very acidic, the bees don’t mind.

      It’s hard to say about the Vaseline. That stuff is fairly inert and I wouldn’t think mold would like it. But if the Vaseline is corralling water or syrup and preventing it from evaporating, it may be adding to the problem. As a general rule, I try to keep non-bee products out of the hive. So although the Vaseline probably isn’t hurting them, I think it might be a good idea to not use it. Prying propolized things out of a hive is a beekeeping fact of life, so I’d go back to that.

      Don’t worry too much about the mold. Are you using public treated water or a private well? I’ve seen a lot of colorful furry fuzzy growths flourishing on untreated well water. Not to worry–most are harmless–but the chlorine in public water kills a lot of naturally occurring molds. Well water may also have metals (like iron) that don’t show up very often unless you let the water sit for a while–like you do in a feeder. On the other hand, you describe fuzzy red spots–and that definitely sounds like mold, so try the vinegar.

  • Thanks so much, Rusty. My city water is filtered via a Kangan machine. I don’t remember if I used high pH or just plain “clean” water.

    Thanks for the vinegar suggestion. I’ve been searching around online and was thinking about adding some essential oil, but the vinegar would definitely be less expensive. It seems like these oils and vinegar (additives) would flavor the honey, but I’ve seen the suggestions in several places now so I guess it doesn’t.

    Thank you, again, for the really rapid response!

  • Chloie,

    If you want the bees to take down syrup to build comb use the trick Rusty taught me. Add some anise extract to the sugar syrup. They are addicts for this stuff. They consume it like there is no tomorrow. Where I live we cannot get splits until mid July. So I always feed sugar syrup to nucs to encourage growth. Right now all my nucs have 18 – 19 combs completely drawn out and are back-filling with honey now. I feed heavy starting out to get the drawn comb and allow the bees to back-fill with nectar/honey so they have natural food going into the winter.

    The golden rod is just coming into bloom here and it is the hottest temperature we have had all year so the bees should finish drawing out the comb. I may even need to remove a frame or two so they do not become honey bound.

    Best of luck.

    • I put anise oil in my sugar syrup. Five days later when I checked the baggie they hadn’t touched it. It was filled with round blotches of mold and the syrup had not been in my fridge over a month. How much anise oil should I use? I’m converting to foundationless so I’m considering feeding them.

      P.S. I’m trying out my friend’s new feeding idea since it is working well for her. Fill a mason jar with syrup and screw it on to a quail (not chicken) feeder. She puts a few rocks on the feeder for them to sit on while they drink. She has very few bees drown this way!

      • Sarah,

        Bees often ignore syrup when the weather is warm and there is plenty of other forage available. After all, they are programmed to collect nectar and that is what they prefer to do. If I do feed syrup in the fall, I use three or four drops of oil per gallon–just so it smells nice but doesn’t knock you over.

  • I’m not getting mold in my sugar syrup, but I’m getting it on the underside of my lid/top cover. Do I clean it with a clorox and water solution? How do I prevent this? (I use Honeybee Healthy in my syrup…which I understand prevents it from mold.)

    • Michelle,

      It’s not uncommon to get mold on the underside of the inner cover, lid, or both. Moisture condenses there because it’s a cool surface compared to the inside of the hive. Moisture evaporates from the syrup or from the bee cluster and condenses on the lid. Any mold spores in the area think they’re in heaven.

      The best way to prevent mold on the lid is to provide adequate ventilation, such as an upper entrance (often cut into the inner cover) or provide a ventilation port in a shim, shallow eke, or a gabled roof. A ventilation port is just a hole in the wood covered by hardware cloth or screen so moisture can get out but critters can’t get in.

      In the meantime, you can wipe the inner cover with a solution of bleach, but unless you fix the ventilation problem, it will just come back. I always carry dry rags with me and just wipe off any moisture and mold. And then I adjust the ventilation.

  • I mix my syrup solution in an old pickle glass gallon jar. I transfer the solution into small 1/2 pint and pint mason jars, which makes it a lot easier to carry out to the hives and these are the jars that I use for the entrance feeders. I’ve noticed a swirling green substance inside my jars-small and large. I’ve read it most likely is mold. Will this mold hurt the bees in any way if it is fed to them? My bee partner thinks not. What do you say? Thanks

    • Debbi,

      A little mold won’t hurt the bees, but if the syrup starts getting smelly I toss it. So basically smell rather than appearance is my cut-off point. It helps to keep it in the fridge, although you can easily get to the point (like I do) that syrup, pollen patties, and swarm lures displace any human food you might want to store.

  • The mold that we get in our bee syrup is caused by airborne spores. The first step in eliminating this mold, is to try and kill any spores that might be on or in the equipment you use to make and store your syrup. I always sterilize my syrup jugs with a bleach water solution before every use, and I bring my syrup to a rolling boil to kill any spores that may be in the pot, sugar, or water. I then lower the syrup’s ph by adding 1 ounce organic apple cider vinegar, 1 ounce lemon juice, and 1 teaspoon citric acid powder to 6 quarts of BOILING syrup. My bees LOVE this formula, which has just a hint of citrusy flavor. They remove the syrup from the feeders before it has time to mold, and no longer have a mold problem even in my syrup spray bottle.

  • The beekeeper who helped me get started told me to add 1/4 teaspoon of vinegar per gallon of 1:1 syrup to prevent mold. I’ve been doing that and I haven’t seen any mold yet, so I think it works well.

  • A method of emulsion I learned from watching the fatbeeman on youtube was to mix a quart of syrup with the essential oil in a blender. Allow the blender to run for a few minutes until the substance appears milky in color. Believe it or not, it actually works and it won’t separate. Also the use of wintergreen oil helps treat varroa and tea tree oil prevents the growth of mold.
    I have family in Florida who keep bees and just started my own hive this year. I live in the northern part of West Virginia and it can be quite cold from October until April with frost thru May. That being said, any advice is appreciated and thanks for this wonderful site.

  • This is my first attempt at honey bees. How late in the spring or summer should I feed them nectar?


  • Just wanted to say thank you for this article. I saw a bit of mold for the first time today when I removed an empty feeder. My son replaced it for me 2 days ago & he isn’t the most careful with such. Needless to say, I have now hot water/soap treated the entrance feeder base and changed the lid out. I’m picky about such things – use a glass mason jar as opposed to the plastic they want you to use – healthier all the way around! I also cook all of the syrup – even the 1:1. I bring it to a rolling boil for at least 10 to 15 seconds in the microwave – then cap & wait for it to seal. I keep it in the fridge once it cools until ready to use – and usually it’s gone in about 36 hours per quart.

    • Ruth,

      Nowadays many beekeepers, myself included, avoid heating sugar syrup. Heated sucrose produces hydroxymethylfurfural, which is toxic to bees. The mold that grows on sugar syrup, however doesn’t seem to affect honey bees at all. Follow the link for an explanation of how it works. When I have to get a lot of sugar dissolved in a little water, like when making 2:1 syrup, I warm it as gently as possible to get the job done, but no more.

  • Is it OK to mix a small amount of Clorox to the sugar syrup to prevent the mold, say 1 tablespoon per gallon of syrup?

  • I just found mold in my hive and thank you for the information about mold. I’m glad to know the bees will take care of the mold.

    My questions are: What about the honey? Is it still good? How do I harvest it safely? Do I just throw it all out?

    • Jim,

      The mold is harmless. You can eat the honey or let the bees have it. To extract, you can spray a fine mist of bleach and water on it, if you want, which helps get rid of the musty odor. Let it dry and then extract normally.

  • I’ve never had a problem with mold in the past but this year I do. Only change I’ve made is this year I stopped using HBH to cut down robbing. My guess is the HBH helps prevent the mold.

  • I question mixing in apple cider vinegar as I have read from several sources that any type of vinegar is harmful to a bee population. I mix smaller batches of syrup in the fall to avoid mold along with putting my feeder in a pot of boiling water or if it doesn’t fit I add boiling water to a feeder to help prevent mold.

    • Alicia,

      I would question your source of information. Honey is highly acidic compared to sugar syrup, which is essentially neutral. A little vinegar will move the syrup slightly closer to the pH of honey, which probably has zero effect on bee health. I would ask the source for their reasoning or their data. If several sources are saying the same things, they are probably parroting each other, a sometimes treacherous internet thing.

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