This is a hot gardening topic these days, and many organic gardeners are promoting the idea that you should add molasses to your compost pile, to compost tea, or even spray plants with it. In tea and on soil, it makes microbes grow, and on plants, it can prevent pests.
Molasses: Should you eat it or use it in the garden?
Molasses, what is it?
Molasses is a by-product produced during the manufacture of sugar. Sugarcane or sugar beets are processed so that the sugar can be extracted. The material that is left after most of the sugar is removed is a black, sticky material called molasses. It contains sugar, some other carbohydrates, vitamins, and a number of minerals like calcium and iron.
It may or may not contain sulfur. You can still get molasses that has sulfur dioxide added as a preservative, but most modern molasses produced for consumption does not contain sulfur.
Is Molasses Good for Microbes?
Microbes are opportunistic in that their populations will increase and decrease as the conditions change. Let’s assume you have not been doing too much in the garden, so conditions are not changing. In that case, the microbe populations remain steady. Things are chugging along at a normal pace, and everybody is happy.
Now you dump a lot of molasses on the garden. Instantly, microbes sense the extra food, and they start to multiply. Bacteria in a lab can divide (i.e., double the population) every 20 minutes. The population is exploding very quickly. All those bacteria need to eat, and they quickly consume the molasses you added. As the food source runs out, there is a massive famine, and most of the bacteria die.
What has the molasses accomplished?
Not much. All of the dead bacteria indeed go on to feed other microbes, and they help build soil structure. The minerals in the molasses stay in the soil, and plants can use them, but your soil probably had enough calcium and iron before you added the molasses. The vitamins in molasses are of no value to plants.
The burst of microbe growth is short-lived and adds very little value to the garden, and it won’t increase the microbe population except for a very short period of time.
You might be thinking that molasses is organic, and therefore it must be good for the garden. Organic fertilizers are good for the garden because they decompose slowly, feeding both microbes and plants over a long period of time. Adding sugar does not do this.
Should Molasses Be Added to a Compost Pile?
It does not add much in terms of nutrients, but people like adding it to grow microbes. As noted above, it does not work since the sugar is used up too quickly. Sugar is also easily washed out of the pile with the first rain.
Will Molasses Keep Pests Away From Plants?
There might be some benefit here if the molasses contains sulfur. Sulfur compounds are known to repel insects.
One problem with this solution is that sugar attracts insects who use it as a food source. Sugar can also lead to black mold growing on leaves, which can harm the plant and attract insects.
Even if the sulfur repels insects, there are better options. Sprays of garlic or onion juice would be much more effective, and they don’t contain as much sugar.
Molasses in Compost Tea
Molasses is a common additive when making compost tea. Gardeners believe that it results in higher microbe numbers, and they are right. The sugar in molasses is candy for microbes, and they gorge on it. I don’t think molasses is any better for this job than white sugar, but maybe?
There have, however, been some interesting studies that show molasses does grow more pathogens, especially in compost tea. “Salmonella populations increased from 1 to over 1000 CFU mlโ1 in dairy manure compost tea with 1% molasses and from 1 to over 350,000 CFU mlโ1ย in chicken manure compost tea by 72 h.ย E. coli populations increased from 1 to approximately 1000 CFU mLยน in both types of tea by 72 h. Pathogen regrowth did not occur when molasses was eliminated or kept below 0.2%.”
Do You Need to Feed the Microbes?
The main reason for adding molasses is to feed the microbes, so it is important to ask, “Is it important to feed the microbes?” The answer is a resounding YES! However, there are many ways to do this. Adding compost, wood chips, or other organic matter as a mulch is the best way. This provides a slow, steady release of food for the microbes.
You also don’t need to add purchased microbes.
Molasses is a product that we can use to feed people and animals. I’d rather eat gingerbread cookies than compost and wood chips. From an environmental point of view, it makes more sense to put non-edible organic matter in the garden and keep the food in the fridge.
There is no “magic” in molasses. It’s just another source of organic matter that will be decomposed very quickly. All organic matter contains carbohydrates, sugars, minerals, and vitamins, just like molasses. Don’t believe me? Consider the fact that molasses is made from plants: sugar cane or sugar beets.
Very interesting arguments for and against the use of molasses. My simple non scientific view would be all about short term gain. Will the use of molasses improve the soil quality to produce a good crop? I used poor quality grow bags to grow tomotoes and need to use a shop bought tomotoe feed or a more organic product? The problem I find with the evidence proof method is that most gardeners are not scientists, and don’t pass down their methods of growing things by writing a thesis paper, they generally pass on their words of wisdom over the garden fence. Most of them have worked for me without a reference.
Soil quality is not improved in the short term. Changing soil is always a long term process.
For growing vegetables you want fast feeding so that the plants get the food quickly before the season is complete. Molasses will not do that for you.
A lot of gardening know how is based on past gardeners knowledge – that is grue. However, this same knowledge has also been shown to be wrong in many instances. For example we no longer use tobacco juice to fight pests – it is just too poisonous.
any improvement in plants life if i added molasses with yeast
Anything organic will produce nutrients that plants can use. The yeast adds no extra value. Use compost instead.
Science has been reduced to propaganda. Studies are manipulated, misinterpreted and cited improperly. When someone uses the word “science” to support an arguement without citing any specific study, propaganda, not science, is being deployed. In 2015, not some, but most of what is being espoused by the medical community is commercial propaganda. As much as we like to think science supports the way we believe, the basis for our societies support for most things is commercial propaganda, not science.
It is sad that you feel this way, but I know you are not the only one. I may use this in one of my blogs and give a fuller reply, without your name attached.
For now let me say two things. If you live in a house, drive a car, and work you are using the benefits of science. If you really do not believe in science – give all of these up.
I agree that there are issues with science – but minor ones compared to your statements. But what else do we have for information? Friends who know less than you? Facebook and Pinterest? Religion? Self beliefs and gut feelings? There really are no other choices for information that come close to science.
Dear Sir
Do you think molasses itself contain any microbs?
Regards
Henry
No. If it did, they would grow in the bottle. once you open the bottle, microbes will fall in from the air. that is why many things are refrigerated after opening.
Microbes are everywhere … no? How could they not be in molasses? Maybe not ones we’re particularly interested in having in our soil though, which is a different question / different issue.
The processing of food is done so it kills the microbes. I would guess molasses is sterilized before bottling. If you pour some out onto the table it will get covered in microbes quite quickly and they will start to grow.
I believe that the molasses and the sugar it contains targets the ever present mycelium that connects to the roots of the plants. That is why the molasses is diluted by water.
This should kick the mycelium into overdrive and provide more goodies for the plants.
When you add anything to soil – it will not target one type of organism over another. It simply spreads out in the soil, and if an organism is present that can use the nutrient – it does so. Fungi and bacteria will both make use of sugars.
I don’t see any logical connection between your idea of feeding the fungi and a reason for dilution?? It is diluted in order to make it seem like you are feeding a bigger area of soil.
Yes the fungi and bacteria and other organisms will be ‘kicked’ into over drive. But once the sugar is used up – the same microbes populations will crash. I don’t see that as being particularly good for the soil.
As far as “provide more goodies for the plants”, the mycorrhizal fungi usually get sugars from plants – not the otehr way around. Granted more fungi, might mean more nutrients delivered to plants – but again this is a short term thing which the sugar lasts.
not short term because it is laying down a system to transport nutrients at the very least.
I wonder if there is a molasses effect on plants not through the soil microflora population directly, but via the locally-produced CO2 from the microflora consumption of the sugar. For that reason, beneficial effects would only be observed in controlled environments like grow houses. Just an hypothesis.
Lets assume the excess CO2 was providing some special benefit. Then any organic mater that the microbes used would produce the same effect. There is no reason why molasses would be special?
Nothing is a miracle cure-all (just a general statement about life). However, the addition of molasses as one-step in an overall organic program can be beneficial.
My theory is a result of personal observation therefore anecdotal at best. While not using extensive controls, I have observed differences in the soils where I added 1) compost twice a year, mulch once a year, organic fertilizer once a year, and 2) molasses immediately prior to adding compost, mulch and organic fertilizer in the same manner as 1). The improvement in 2) over a 2-year period was observed to improve at about twice the rate of the soil where no molasses was added. That “twice” the rate comment is not very well defined, but here’s the observation: I started with heavily compacted, moisture-less clay and shale soil (virtually a giant brick). The above protocols worked wonders. I now have a good layer of relatively rich, airy soil with earthworms (appeared on their own) and the plants this spring are emerging vibrant and healthy. The soil in areas 1) and 2) are strikingly improved over their beginning state. The average depth of the improved soil in 2) is about twice that as in 1). Both areas together total only about 375 square meters, so I don’t perceive any significant difference in the beginning state of the soils.
It occurs to me that the molasses is working as an accelerator (please pardon my lack of appropriate vocabulary). Possibly from increasing the microbial activity earlier in the year to the level the organic material will carry. The improved soil appears to be the same quality in both 1) and 2). Without knowing how to test the soil I can only make that generalization. But the volume of the improvement is noticeably increased in 2). My prediction is that once the soil has reached a good microbial/organic material balance and overall level and depth, the benefit from the use of molasses will decrease, possibly even disappear. But in this particular case, it appears that a benefit was derived from using molasses. I will continue to treat both plots as outlined to see if there is a continued benefit to the addition of molasses, or if the difference in the soil subsides as time passes.
This is offered in the spirit of receiving thoughts on the process so that I can learn more from it. Not to contradict anyone else’s assertions.
Molasses, being mostly sugar, is easy for bacteria to use as a food source. It should produce rapid growth of bacteria, and if other organic material is added at the same time it is possible that this growth in bacteria also speeds up the decomposing process of the organic mater. I’ve just been working on posts about compost making, and ‘accelerators’ don’t seem to speed up the overall process – at least I did not find any reliable references that have found this. It is possible that soil is different but I suspect it is not.
Well I do not find the argument debunking molasses any improvement on the arguments in favour. I have seen positive statements about molasses for control of nematodes backed by nematode counts. I have a very sandy and water repellant sand for my garden soil and I would rather apply molasses in the hopes of some small improvement than accept any argument against that is not supported by good evidence and not speculation. Molasses is not just sugar as many critical of tis use seem to suggest.
Molasses is 50-65% sugar and most of that is sucrose. My statements about adding sucrose to bacteria is a well known fact. They grow rapidly on the energy source, and once it is used up they crash. I just don’t see how that is good for soil?
In my research for this post I did not find any scientific studies that showed molasses does anything positive for soil, but if you have such references I would love to hear about them.
I have never heard about molasses controlling nematodes. Do you have a reference for that?
Thank you Robert, I simply googled molasses as a soil treatment and on the first and only page I looked at saw a reference to a “scientific” publication that dealt with the application of molasses for nematode control – with note of a positive response in respect of nematode counts. As a once upon a time agricultural entomologist it was common knowledge that sugar was an effective nematode control product. Besides what happens to all the other plant nutrients in sugar cane after the sugar is boiled off – do you speculate that they are not available when applied to the soil in molasses? (four forms of cane molasses?) Curiously I used molasses to bind the clay of tennis court surfaces with spectacular results – a surface that was better than either bitumen or concrete surface then in vogue. As a scientist I recognise the necessity of scepticism BUT ‘organised scepticism”. This organisation has to recognise that this is a conscious creation and that the mind stretches from the universal to the individual – anything is possible if the mind can be focussed to a particular end. I would far rather try molasses than simply accept that someone dismisses the possibility that it might work under some or other set of conditions. Neither would I put all my eggs in one basket or accept that there is a limited preferred set of options for improving soil condition or structure. As a horticulturist I learned very quickly that there is really something called “greenfingers” and that there is no single way of growing anything very well – people produce remarkable results doing very different things. Soil is probably one of the most complex things on the planet and it is just miraculous how forgiving it, and plants, are. Myths are very useful things and it might be more useful to explore their origins before dismissing them on ones own observations.
The myths I write about are rarely debunked by my own observations–I use published references and accepted science for that.
As for looking at the origins of myths–I also do that have started publishing on them. For example https://www.gardenmyths.com/garden-myth-born/ More of these will be in posts this year.
Keep in mind that I have said molasses will not do some good in the garden. The message I hoped was clear is that molasses is not some miracle magic gardening potion as it is made out to be by many sources. Unless you have cheap access to it in large quantities is not an environmentally friendly product to use, since it is better used as a food product. Use compost instead.
An initial review of molasses and nematodes does indicate that they may be effective but the studies I found were not good quality peer reviewed work. It is interesting that another topic came up this week–the ability of some types of nematodes to kill slugs and snails. So if molasses does decrease nematode populations, it might just also increase slug populations. I’ll be looking into both of these topics in future posts.
Robert I think we are talking past one another. I did not think (i.e.my perceptions were) the reasons you gave for the use of molasses being mythical were correct or accurate. But I think where you really are wrong is in suggesting that published science, or science as practised, can be depended on to save our sanity and money. My experience (and I worked for many years as a senior technical advisor for a leading crop protection supplier (covering the emerging Monsanto products as well) and long enough to learn that science gets seriously bent when profit is at stake. Furthermore, science debunks anything in the fields of intuition, sixth sense, metaphysical, paranormal etc. and this is glaringly wrong. Have you read the Magic of Findhorn, or Michael Roads “talking with plants” or Lyall Watson’s works and explored in anyway the countless stories that suggest (if no thing more) the immense power that lies in image and belief? For me the joy and ,magic of gardening and growing things is thatoy and delight can Do things. I “like “molasses” and am happy to regard it as a high energy product that feeds things that live in the soil – even for a short while. I also use every other method that I “feel” might be close to nature – to hell with what some technologist materialist might want me to spend my time and money on.
Re: “Furthermore, science debunks anything in the fields of intuition, sixth sense, metaphysical, paranormal etc. and this is glaringly wrong. ” It seems you and I have completely different belief systems. If we are not going to believe science–then we should not waste our time doing it.
The goal of GardenMyths.com is to look at gardening information from a scientific point of view.
Robert I believe firmly in science and the principles of science.- it these are not applied you cannot call the product science. I know where science originated and I can see how misguided we have become by blindly following what “scientists” report. If scientists are needed to explain what the different forms of molasses are, then we are in sorry mess. What molasses has 50% sugar and just what do you mean by “sugar”? This is inaccurate “speak” One should not have to be classifiable as a scientists to recognise this.
Gosh Robert – you may believe in science. I try to apply it in the way I think and act in every aspect of my life. Belief has no place. I also apply science to what you write, and I value and enjoy that whatever disagreement I may suggest.. I think you do tend to make sweeping statements that are no better than the ideas you are trying to set aside. How can you for example say “explosive growth for a short time is never a good thing”? I am sure Stephen Gould would have said that in biology you should never use the word “never” following his statement that the strongest statements you can make in this field is “hardly ever”. Biology is rife with “events” that drive change and just what change is good or bad?
Maybe the molasses is a thing weed growers use to temporary boost their crop performance.After all I think it harvests in 2 months.Haven’t you thought of this as a reason for the myth.I’ve hear baking soda and vinegar bombs for weed plants too lol sounds crazy to waste so much on voodoo horticulture methods rather than just use chemicals that produce co2 safely and efficently.I guess I can rant nuclear power is the most environmental conscious if it were a perfect world. But we all no how dangerous people can be with gasoline another safe chemical. I like you’re blog but I think you need to look at the history of how we ended up with this monkey in the molasses business.
I looked at some of the comment above and I think Robert is also wrong in what he says about molasses being a food product belonging in the fridge. “blackstrap” molaases is widely espoused as a health product and sold as such at quite a price. But you can but it in bulk as the final product after complete sucrose extraction when it is sold as an animal feed additive. In fact before it became fashionable for animal feeding it was even cheaper which is why it was used in clay tennis court construction and maintenance. When added to soil it does not simply leach away as sugar and definitely not sucrose of which there is minimal in third boiled cane juice. If those microbes have used it they have sequestered (captured) carbon and that is what we want in soil with everything else that organic elements may contribute to any life in and from soil.
I did not find a product that is called molasses were all of the sugar has been removed. Can you provide a link to such a product?
When gardening advice posts on the internet talk about molasses I am quite sure they are talking about the common molasses available to the average household, which has a high sugar content. That is the molasses that is discussed in this post.
The term sequestering carbon is usually used to refer to the capture of CO2 and holding the carbon for an extended period of time. Using this definition microbes do not sequester carbon. Most microbes are bacteria and they have a very short life span. When they die, the carbon in them becomes available to other creatures in the soil–there is no long term storage. Good garden soil is aerobic, ie has oxygen. Such conditions favor the growth of aerobic bacteria with produce CO2 as they grow. So an increase in bacteria will actually produce a net amount of CO2–not sequester it.
Molasses is not 50% sugar. You’re out of your mind guy. Black Strap Molassess is VERY low in sugar. Less than 9%
I don’t think I ever said it was 50% sugar, but from Wikipedia “Beet molasses is 50% sugar by dry weight, predominantly sucrose”. And from Yahoo answer “The total sugar content in molasses is approximately 50 %”. and from the research paper, THE COMPOSITION AND CALORIFIC VALUE OF SIRUPS AND MOLASSES DERIVED FROM SUGAR CANE – total sugar is 60%.
? Explosive growth never a good thing? Nature is not slow and steady. Take rain for example. You have no control over it. Its timing, quality, or duration and its usually not a slow and steady shower. What is real science? Indisputable proof at a specific point in time. Well time changes, that’s a fact. Or does it?
For the most part nature is slow and steady. Heavy downpours of a lot of water are the exception, not the rule.
I don’t agree that real science is “Indisputable proof at a specific point in time”. In fact it is the opposite. Science is a description of laws that are followed over long periods of time. The ‘proof’ science develops is a way to predict the past, present and future–not to only describe the present.
There are scientists and there are non-scientists. The scientists are a special bunch, usually stubborn, hard headed pragmatic type. They tend to hold on to their precious knowledge possession tightly, comforting themselves with a thought that science is the only true method of explaining things. Very valid point, indeed. The problem is that the real science is seldom. What we have is a structure of scientism where participants (scientists) fail to recognize that the foundation for their work rests mostly on fundamental assumprions. Maybe there isn’t anything more reliable than the scientific facts. But Mark is right. whatever is considered an axiom today would have been laughable a hundred years ago. And those scientists back then were just as sure as the new ones are today. Just to have been proven wrong by their grandchildren.
I would disagree with “stubborn, hard headed pragmatic type.” They are rarely pragmatic, and most are open to change – they just want some proof.
The whole basis of science is the evolution of facts.
” Heavy downpours of a lot of water are the exception, not the rule.” – you are not from Louisiana I see.
You say to leave food in the fridge- but the best composts come when including food scraps from produce. Also the reason to add molassas is not because of microbes but because sugar is hydrophilic – it holds water and prevents water loss due to evaporation, making it available to the roots longer and preventing repeated stress of too dry soil between watering a. You don’t add granulated sugar water because white sugar is bleached with chlorine which isn’t good for your plants because it will poison the microbes leaving the soil dead microbe wise.
Yes–food scraps should go into the compost. A bottle of molasses is not a food scrap. It should be used as food, not for making compost. In my mind it is unconscionable to use good food to grow pretty flowers, when people around the world are starving.
The idea that you are uses molasses as a way to prevent water loss makes no sense. First of all you are adding very little molasses to the soil. If it would hold water it would hold very little since there is not much of it there. Secondly, microbes digest sugars easily, and it does not hang around for very long before they use it up.
White sugar might be bleached and chlorine may be used in the manufacturing process, I don’t know this for a fact, but if this were true, the chlorine is mostly removed before it is packaged. If this was not the case, you would smell the chlorine when you open a package of sugar. The small residual amounts that might be left will have no effect on microbes.
Micro-organisms feed on carbohydrates, but molasses (sugars) is a highly concentrated source of carbohydrate energy, compared to other organic material (such as leaves, still needing decomposition to be used as energy source for bacteria). By adding molasses (or molasses-meal) to soil, you actually induce an explosion in the population of soil microbia. These micro-organisms die after depleting the sugars and by doing so, their bodies (protein or N-releasing material) become part of the new ‘soil’. The soil structure will be much better and may change a poorly-drained soil into a much more productive ‘well-drained’ soil. By improving the aeration of a poorly drained soil, the production potential of that soil will be improved. (Dr. Nic Combrink, retired Agronomy lecturer, Stellenbosch university, South Africa).
What you say is mostly true. You will only see an explosion in growth if there is enough nitrogen present to support such growth. The reproducing microbes also need nitrogen. Since nitrogen is also the most critical nutrient for plants, it is quite possible that the explosive growth robes nitrogen from plants–in the short term– and this is not good for the plants.
I would not agree with the statement that “The soil structure will be much better”. I am having trouble with the word “much”. A single application of anything to the soil will not make soil “much” better. It is true that over time the soil structure will be improved. But that happens with any organic material added to soil.
Explosive growth for a short time of one form of life in the soil is never a good thing. Slow and steady makes for a much better environment for microbes and the plants.
Let’s assume the extra sugar is good for the soil. How much should be used? I checked various web sites and found a range of values from 12 ml/L to 32 ml/L. that is quite a range. What is most interesting is that almost none of these sites indicated how much soil area is to be covered by these mixtures. so you can make up a mixtures in a variety of concentrations and apply them onto any area of soil and expect results??? this kind of science usually indicates that people are guessing, and that they don’t know how much to use, because no real science has been performed.
I did find two sites that had the area included. One suggested 7.5ml/sqft, and the other 0,05ml/sqft. At 0.05ml you are adding basically nothing. Since molasses is about 50% sugar, at the 7.5ml value you are adding less than a teaspoon of sugar per square foot. That is also not very much sugar and will have limited affect on soil structure.
As I said in the posting, there is nothing wrong with adding molasses to the garden. It is just not the best option for building soil structure.