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.
Have you ever heard of applying molasses and liquid carbon to root zone
What is liquid carbon? There is no such thing.
They never stop to ask… Which microbes (in the soil) are actually feeding on the sugars?
Beneficial soil bacteria do not feed on sugar. Yeast, on the other hand – will ferment the sugar into alcohol which I’m sure plants do not enjoy very much. This unhealthy competition in the soil will likely kill-off the majority of beneficial bacteria (like fungi and nitrogen-fixing bacteria); who suddenly have to compete with an “explosion” of alcohol producing yeast. I just cannot (for the life of me) imagine how this would help your garden at all. Which is why those claims are always conjectures from people who can’t even grow a common weed.
Anyway, plants cannot absorb sugars through their roots and the bacteria that feed on sugar and refined carbs are actually damaging to the complex soil microbiota. Plants did not evolve to live in ‘candyland’ and they don’t need a beer to take the edge off. -I’m sorry people.
‘Organic’ – It’s a buzzword for a sales pitch in this case. Just because something has a carbon atom doesn’t necessarily make it “safe and effective”. Gasoline is technically ‘organic’ by that same token of ignorance. The overwhelming majority of nutrients that plants absorb are INORGANIC MINERALS. Normally supplied via complex bacteria in the decomposition of organic matter within in the soil – but the minerals themselves are (and remain) 100% inorganic.
I’m not attacking ‘organically grown’ – merely pointing out the misconception surrounding the word itself. Because molasses is organic in the sense that it contains carbon – like gasoline or other hydrocarbons, it is ‘chemically organic’ – but not in the ‘holistic sense’ of the word used often by organic gardeners. When gardeners say “organic” they are generally referring to the method of production involving natural systems. There are two different definitions. However, molasses is just as ‘synthetic’ (in the holistic sense) as any off the shelf miracle grow fertilizer. Which will give you much better results anyway. Urinating in wood ash is totally free and will likely also give you better results than molasses hands down!
That being said, if you’re you’re looking for that next ‘miracle breakthrough’ in plant fertilizer – Then look no further. Worm castings. I bury a 5-gallon bucket up to the lid in my raised beds that I drill full of holes. I compost kitchen & garden scraps inside the bucket and my entire grow bed becomes a living ‘vermiculture’. The worms work tirelessly without pay- devouring the food scraps I throw in the bucket and then actively transporting those nutrients directly to the rhizome; no tilling or fertilizing necessary. The worms keep the soil structure pristine and full of vitamins, minerals, and L-form amino acids that make plants go CRAZY. No amount of molasses can ever compare to this. So you people keep your molasses – I’ll be farming my worms ๐
Although I agree with your general sentiment, I don’t agree with all of your statements.
Re:”Beneficial soil bacteria do not feed on sugar” – can you support that statement? Lots of bacteria are cultured on media containing sugars.
Re: “This unhealthy competition in the soil will likely kill-off the majority of beneficial bacteria (like fungi and nitrogen-fixing bacteria)” – this is not likely to happen. There are too many bacteria and they rebound quickly as the environment changes. Fungi are not bacteria.
I just added mollases to my plants two days and they went nuts! The aroma was not there two days now’s it’s like boom. One plant also caught up with the other plant.
Plants don’t grow that fact.
I keep seeing you appear to acknowledge a benefit but repeatedly dismiss the potential benefit by stating “once the sugar is used up”. Did you think for a moment that people may actually use it as a part of a continual feeding cycle? It appears as though you base your opinion on a one time use. With regular feeding during the growth season how can this not be beneficial? Of course long term soil health is the key and compost, leaves, woid chips etc to build a thriving soil full of life is the goal but during the growing season supplementing with molasses regularly cannot hurt it can either 1) help or 2) add no benefit. It seems clear from everything i read that there Is a benefit so rather than continue to keep resorting to “when the sugar is gone” explain how a mild and continuous addition of molasses is not beneficial.
You are correct. If you add more molasses before the first batch is used up you can continue to feed the bacteria explosion. How frequently do you need to add it? The people who promote the use of molasses do not say that it needs to be applied frequently nor do they have data showing what ‘frequently’ is.
Lets say you are adding sugar regular enough to maintain a higher than normal population of bacteria. Sugar contains carbon, hydrogen and oxygen. In order for the bacteria to live they also need all of the other nutrients, especially nitrogen. As the population of bacteria increases, the available nitrogen available to plants decreases. So too much sugar will starve your plants of nitrogen.
If you want to feed bacteria you need to provide a balanced diet.
I have heard that this is similar to the reason why you don’t add raw sawdust or woodchips to the soil before planting. The bacteria will increase to deal with the over abundance of carbon which will then starve the plants of the nitrogen they need.
You should not add large amounts of wood to soil – but for a different reason. Wood is high in carbon and low in nitrogen. This does not support bacteria very well. In order to live, bacteria need to find extra nitrogen which they get from the soil, robbing it from your plants. Long term the wood decomposes and is good for soil, but short trem it can harm your plants. Better to compost the saw dust, and mulch with the wood chips.
every other watering or at the least every 2 weeks i would reapply the molasses for a plant. what bought me here was composting. interesting thoughts disagree on some of it. but from what your saying added continuously to a compost pile would break it down. have you read teeming with microbes? great read would love to pick your brain and think its cool you reply to the comments
I have not only read Teaming with Microbes, I have written several critiques of the book.
The basic information presented in the book – the importance of microbes – is very valid. Unfortunately the author follows Dr. Ingham’s teachings too closely without looking at the validity of some of the concepts.
If you would like to ask specific questions come over to Facebook and start a discussion. https://www.facebook.com/groups/356927494777686/
https://www.gardenmyths.com/teaming-with-microbes-close-look-part-two/
https://www.gardenmyths.com/teaming-with-microbes-close-look-part-one/
https://www.gardenmyths.com/teaming-with-microbes-book-review/
I live in Thailand, where friends have used molasses (food grade or agriculture grade … I don’t know) as a source of sugar / food for microbes while making microbial inoculants (which, I realize, Robert doesn’t consider very highly). Some of these people have reported that a hard layer forms below the surface of the soil, that they attributed to chemicals used during sugar processing that remain in the molasses. No scientific data, for sure, just anecdotal reports here.
I have been debating if I should continue with adding molasses to my garden/yard. Ive noticed a lot of the molasses as a wonder drug is propogated by radio show hosts who also own garden centers and need to create demand for the products they sell. Products like green sand, fish emulsion, and seaweed extract are much the same to me. The garden industry is like any other industry.
At $10 a gallon for molasses that lasts me a year, it isnt breaking the bank. And I potentially do add some benefit to my garden, to whatever unknown degree. And for that reason, i may keep it around.
http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.381.8407&rep=rep1&type=pdf
Here is another study on molasses usage as fertilizer.
1) Where was this published? It is not clear.
2) It is not really a study. The report looks at costs and compares fertilizer costs to molasses costs. The costs discuss are costs that a farmer in S. Africa would pay if they are growing sugar cane. According to the report there is a special price for these farmers – see paragraph above table 1.
3) This study makes no mention about feeding and growing microbes which is the topic or the original post.
4) The study does make claims about increasing soil structure etc, but the report (a) does not study any of this, and (b) it does not provide any data that would support their claims. In fact the report does not indicate that any field testing was done.
5) The study says that organic matter is added to soil via the molasses, but the only organic matter being added are sugars. The lack of proteins and other complex molecules – see table 2 – means that this organic matter has limited value to the soil, because it is missing most of the micronutrients.
The study shows that molasses contains 4 % potassium. This would have some value as a fertilizer. Is molasses cheaper than Potassium chloride fertilizer where you live? Do you need K to be added to the soil? If molasses is a better price, and you need to add K without N and P, then maybe this makes sense as a fertilizer.
Of course, it will not work always and everywhere. I just thought that it was interesting.
Here is a study on using molasses on tomato plants:
http://www.irjabs.com/files_site/paperlist/r_2136_140515005418.pdf
Conclusion:
The results showed that sugar beet molasses and Fulvic acid had significant effects on Shoot fresh weight and nutrient uptake compared with control. In this respect, the impact of fulvic acid on quantitative and qualitative characteristics of plant was greater than molasses. Accordingly, the use of these compounds in agriculture for improving soil fertility and plant yield can be considered.
Another thought; the cheapest way to add molasses is to use farm grade, not food grade. It is an animal food additive. And as far as using food that could have gone to starving people in gardens; if the garden produces more food it is a net gain.
Only if the excess amount of food produced equals the amount of molasses used. In this case the excess food produced would have be be more than what the garden produces without molasses.
Microbes need carbon; this is true. Carbon can be found in both wood chips and in molasses; this is also true.
But: the carbon in molasses is quickly available, and water soluble, which the carbon in wood chips is not.
I can see at least two possible uses for molasses; speeding the cycling of nutrients in the soil, and feeding the leaf surface ecology.
In the soil, the rapidly available carbon will fuel a boom bust situation; even before the carbon runs out, numbers of protozoa and nematodes will ramp up due to more bacteria to prey on. As the bacteria die or get eaten, the other elements that they absorbed will be released to the plants. Fueled by the carbon in the molasses, they will break nitrogen out of organic matter to build their cells. Plants can only use mineralized nitrogen, not nitrogen fixed in organic matter. So as the bacteria die or are grazed, mineralized nitrogen will be made available. The same may happen with other nutrients, though there have been more studies done on nitrogen. In other words, the nitrogen cycle is speeded up, much to the benefit of plants.
As far as feeding microorganisms on the leaf surface, the carbon in molasses is much easier to apply then wood chips. Keeping a bunch of beneficial organisms in a functional ecosystem living on the leaf surfaces will ensure competition for disease organisms when they show up. Many proponents of applying molasses are also advising the use of compost teas or microbial inoculations on the leaf surface; the molasses will give them the energy to thrive.
Another point is that proponents of molasses sprays often advise small frequent doses, which would avoid a boom bust cycle; it should in theory keep a greatly increased microbial population going on the leaves.
Finally, I have not yet used molasses; I was hoping to find some side by side test, and was disappointed that this article didn’t reference any. I will do some and post the results.
The reason there are no references is that scientists do not take the use of molasses seriously. So they do not spend the money to do the testing.
Molasses use is one of those things that a fringe group promotes with no science backing them up.
Comparing molasses to wood chips the way you are doing it does not make sense. Wood chips are a slow feed for microbes. Molasses is a fast feed. Different product for different purposes.
You brought up the fact that carbon could be added with other forms of organic matter, such as wood chips. I was simply pointing out that the carbon from molasses would have a rather different effect; and apparently you agree with me.
I don’t agree that carbon from different sources would have different effects – carbon is carbon.
But it is not carbon that is the chemical of interest. Carbon is found in many different chemicals and each chemical will have a different effect.
Your categorical assertions do trouble me slightly and appear to be both incorrect & unsupported by available data – as long as you treat molasses as source of sugars and other trace elements.
Published in Journal of Arboriculture 30(6): November 2004
http://www.barchampro.co.uk/sites/default/files/percival_2004_sugar_feeding.pdf
The study you refer to was testing the addition of sugar to trees growing in pots. Each pot, of 1 gal size, received 25 grams of sugar, on average.
The study found that trees did grow better with the sugar added. But there are two problems with using this study to understand the addition of molasses to a garden.
1) In order to saturate a garden so that each gal of soil received 25g of sugar you would need a truck load of molasses – the pro-molasses people do not recommend using anything near that much.
2) The testing was done in a lab in pots. You can not translate their findings to a garden situation.
Thanks for posting the article – I happened to see it earlier this week and do plant to write about it at some point.