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.
I have used molasses side by side with fox farm. Both plants side by side, you wonโt be able to tell me which one has expensive nutes and which one is molasses. Unlike just writing a random article, I actually did some test runs. Molasses appears to do just as much as the 100$ Fox farm nutes. No science involved, just good old fashion growing and knowing my plants. All this being said, you do state that โmay have short term benefitsโ and my grow is indoor so short term is all thatโs needed. Your article even though you may feel good about how you did, itโs really not helpful or informative and like you stated above… You can believe whatever YOU want, that donโt make it right๐๐… good try but swing and a miss with this one. I will say that my results are from growing cannabis (legally) so maybe on vegetables and such you could be correct but when growing pot, this article just confuses people that stumble across it first and donโt already have a idea whats really going on. Hell, Iโm not sure how I even ended up here.
But you did not try just growing them with nothing – they might have grown just as well that way.
How many of each did you grow? Enough to get some statistical data? If not, then it is just anecdotal information.
My information is science based – you do not have to believe it.
I’m laughing at the fact that you deny that this is useful information, while also heading your argument with the fact that there was no difference between overpriced nutes and molasses. This is truly a great example of people believing whatever they want even in the presence of zero practical evidence. Have you considered that neither the ‘luxury fertilizer’, nor the blackstrap molasses made a difference because there were sufficient nutrients in your overpriced soil? Try the fox farms soil alone, or retry the same experiment but with an inert medium. I can bet you will notice a difference between molasses and actual nutrients then.
Outsmarting yourself again ๐
The REASON molasses WORKS is because it causes a Microbial explosion in the soil- these microbes break down the NPK so that its more readily available and easily absorbed- dont believe me- READ the scientific studies on the use of molasses on pasture land- its proven very effective but not sustainable because of the amount needed to do a pasture FREQUENTLY. If you are doing potted plants its HIGHLY effective- enough said…
It is clear you did not read the post! I said as much – but it is a short lived process that is not of much value.
I’ve heard from master growers that they add molasses to their compost stew and water their plants with that. i will take the words from a master grower over some blog any day.
Master Grower vs Science – choice seems clear to me.
Honestly, as a new grower in Waterloo that is thoroughly confused by all of the massive shelving of ingredients I’ve been accumulating in hope of running a successful indoor organic soil grow — I actually find this blog refreshing.
A bunch of times now, when I’ve gone to search for how to use one of these things, I am lead to posts on this blog..
It’s probably not what a lot of people want to hear but I’m a skeptic by nature, especially when it comes to trying to “understand mother nature”
So honestly — thanks, it’s hard to come by ANY differing opinions, just a lot of repetition
Are you a gardener Robert? It is one thing to trawl through acres of science articles, all referring to their specific contexts which may or may not be relevant to a particular garden or gardener. However a balanced opinion will necessarily include a lived experience of the topic, ie, your own gardening successes, failures, experiments, etc. You donโt seem to mention them, only someone elseโs studies. It is hard to respect this abstacted commentary. What about your OWN results?
I’ve been a gardener for more than 45 years.
My personal experience is not of much value when trying to understand a topic, for the same reason other people experiences have little value. We rarely run controls, and almost never run proper controls. That means our results are meaningless in terms of being scientifically valid. They certainly play no role in understanding the topic.
They are just anecdotal information.
I’m sorry. I have no firm opinion either way. But I do see what to me at least appears to be ego forcing you repetitively back into the “molasses shouldn’t be added” camp despite the fact you admit, in response to several comments, that there “may be short term advantage”; but then in other places claim it is of no value and that no *real* science supports using it (as if we can be certain of who is truly behind either the direct or indirect money involved in the studies you or anyone quotes); then dispute any studies or papers anyone else posts stating that “real scientists don’t take using molasses seriously.” Forgive me for saying so, but you are more dogmatic it seems than any other post I’ve read to date thus far above… that being a dozen or two. Thus I will continue my research… mostly elsewhere for now to find those less likely to be prone to “the earth is flat” theories being called fact in the apparent self admitted absence of studies you consider unflawed.
I don’t see a conflict between “molasses shouldnโt be added” and “may be short term advantage”. I have clearly stated the sugar will feed the microbes short term – which is a short term benefit. There is no long term benefit, so it does not make sense adding it to gardens.
If adding molasses to the garden provides short term benefits and I keep adding it to continue the benefits, doesn’t that equate to long term benefits over time? I don’t really understand the author’s logic on this.
True – but I have yet to see anyone recommend adding molasses every few days to a garden. And why would you do this? Almost any other standard organic source like manure and compost will work even better and cost a fraction as much.
I have used molasis for the last 3 years or so. I have since switched to Advanced nutrients bud candy. I can tell you hands down that during the flowering phase molasses had increased the growth rate up. I also noticed that when used side by side with a plant that hasnt had any the roots on the one withouout have less fine hairs on them and less overall mass. Im no scientist or professional. I have no expeertise in anything, but I can however tell you what I have seen time and again every few months for the last several years.
People believe all kinds of things – does not make them true.
I have a few questions I don’t see answered here:
1. Are there nutrients in molasses that are directly beneficial to plants such as phosphorus and potassium?
2.Could that affect root growth as reported above?
3. Molasses is often added to compost tea. Is that necessary?
1) Yes – anything plant or animal based material will contain some p and K.
2) Only if the soil has a shortage of P or K.
3) No, and compost tea adds no benefit to soil over and above the compost or other organic matter added.
https://www.gardenmyths.com/compost-tea-does-it-work/
I use Molasses and I am very happy with results. If nothing else makes it smell better… bigger flowers….. more trichomes. If it is temporary boost for microbes itโs still helps. If your a nay sayer just donโt use it. Iโm not going to stop because you donโt agree.
I realize this is an old post but what the heck…its a continuing topic of debate so here goes
Studies are rare- but those that I have read that involve science all state there was no increase in yield when adding molasses to crops…Problem with science is it leaves out TO MANY variables.
1- Molasses feeds Microbes…so one application is of little value-however as cheap as molasses is I add it to my 210 watering tank EVERY watering although in a weaker solution than others use in 1 time applications. I figure keep feeding microbes it keeps doing good.
As for the microbes depleting my nitrogen-I transplant plants- then top dress with rich cow manure thats to rich to actually grow in. I add drip irrigation over each plant. I am not using any commercial fertilizers. I dont care if something is organic or not- I care about not blowing a bunch of money on fertilizers and not knowing if my soil has too much or not enough. I add the manure then feed the microbes that continually break it down and each plant “takes what it needs”
The sugar fends off many bad insects-I like that and its obvious. I know SCIENCE is the basis for the article/blog so i can tell you I have read scientific studies that overwhelming found that the ladybug population explodes when adding sugar to a foilar feed- even their egg production skyrockets…not sure why- as the science concerning insects and sugars seems to contradict itself here… still I dont have to understand “why” things work ( although i think about it a lot) Just SEEING it work is enough for me
Thats pretty much it…it works great. No harm in plants getting the extra potassium in the molasses for bigger flowers
I also ‘witch” a water well before drilling it :)…I dont have to understand the science or even if the science makes sense- I just know it works
You are using the science you know, some of it is correct, and reaching a conclusion. In science we call that a hypothesis. Now you need to do proper experiments to determine if the hypothesis is correct. That science has been done, and “those that I have read that involve science all state there was no increase in yield when adding molasses”.
On a bit of a lark, I added a bit of molasses solution to my compost pile in the fall of ’16, and was surprised at how quickly the leaves broke down. I’m at 6,000 feet in Wyoming, and previously the leaves took all winter before I could easily work with them, even with regular efforts at shovel turning. The molasses simply accelerated the process in a big way. For that, I’m appreciative of the benefit of a couple bucks of the brown stuff.
hi- Bos. If a sugar boost to speed decomposition is all that’s wanted- maybe just add damaged/unwanted fruit, either self grown or wild collected. Then you’d save both the money and wasted energy/packaging/emissions from buying products.
You might also find that, easier still, a few milk bottles of urine does the job- since dropped deciduous leaves are likely to have a higher carbon to nitrogen ratio than green, and thus an N boost would be of more value than a sugar boost.
Mr. Pavlis,
Indeed, thank you for refuting this molasses nonsense. I am an agricultural scientist and in my seventh decade of life, and never heard of a better joke. I have not only had academics in the subject (2 years of grad. study to boot) but also my family owned a 30-thousand-acre ranch, with vineyards, fruit orchards, grain, alfa-alfa, and other feed- crop fields. Sugar in the soil? It is bogus.
I was a member of Huntington, Descanso, LA Arboretum and other botanical gardens during my stay several decades in Southern California. I had contacts with their gardening staff, and botanists about the nitty-gritty to have heard of it.
This is like naming the bacteria (chiefly lactobacillus bulgaricus) that digests the warm milk and converts it into yogurt, with a marketing name of “probiotics” and inventing a marketable a new nutritional supplement. Funny thing is, if you eat half a cup of yogurt a day your intestines will be rich with that bacteria, and you will get all the probiotics next to nothing.
As to sugars’ effect on microbes: without any doubt in my mind it is a very harmful practice. These are why: 1) We have no idea how earthworms will react to sugar, it may change or kill them. 2) We should not multiply bacteria by molasses, when the ordinary sugar broken down by the bacteria, what is left is not useful to the plants. When there is plenty organic matter in the soil the bacteria population will multiply and they will break down the natural fertilizers, and other organic compounds and free the nutrients such as Nitrogen, Phosphorus, and other elements. If bacteria breaks down the molasses their usefulness will bypass the very purpose intended.
Did you ever research further into the effectiveness of sugar (including molasses) on controlling root-knot nematodes? I’ve used raw sugar dissolved in water on my sandy soil and it does seem to keep the pests at bay, whereas without it plants like okra and tomatoes never thrive.
no.