Molasses for Plants

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Robert Pavlis

This is a hot gardening topic these days and many of the organic gardeners are promoting the idea that you should add molasses to your compost pile and to your garden. It makes the microbes grow better–they need to eat, don’t you know?

Molasses; should you eat it, or dump it onto your soil? You have come to the right place to get the facts.

Molasses for Plants
Molasses for Plants

Molasses, What is it?

Molasses is a by-product produced during the manufacture of sugar. Sugar cane 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. Molasses contains sugar, some other carbohydrates, vitamins and a number of minerals like calcium and iron.

Molasses for Plants

You probably know that it is important to have microbes in your soil. If not, have a look at Organic Fertilizer – What is its Real Value. If having microbes is important, than it makes sense that you should feed those microbes. Feeding them will make them healthy, and make them reproduce so that you have even more microbes. Guess what? Microbes, especially the bacteria, love sugar. It’s no surprise that they also love molasses since it is mostly sugar.

Plant Science for Gardeners by Robert Pavlis

So far it all seems to make sense. Microbes are good for soil, and molasses is good for microbes, so why not add it to soil? The short answer is that there is nothing wrong with adding molasses to your garden, or to your compost pile. It will feed the microbes.

Does it Make Sense to Add Molasses?

I’ll save you the trouble of skipping to the end of this post–the answer is NO!

Understanding why the answer is no will help you understand your garden. Let’s have a look. In a normal garden, or compost pile, you have a large variety of microbes, all going about their daily lives. They find something to eat, they poop, and they die. This is a continual process that goes on a billion times a second.

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 (ie double the population) every 20 minutes. The population explodes 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.

Molasses causes a population explosion, which quickly dies down once the sugar is used up.
Molasses causes a population explosion, which quickly dies down once the sugar is used up.

What has the molasses accomplished?

Not much. It is true that all of the dead bacteria 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.

Is the massive population explosion good for your plants? I don’t think anyone knows, but most things in nature are better off without massive changes, and plant roots depend very much on the population of microbes around their roots. I just can’t believe a bacterial population explosion is good for the plants.

Building Natural Ponds book, by Robert Pavlis

Molasses might make your compost pile work quicker, but the first rain, or your hose, will wash the sugars out of the pile removing any benefits.

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 ml−1in dairy manure compost tea with 1% molasses, and from 1 to over 350,000 CFU ml−1 in chicken manure compost tea by 72 h. E. coli populations increased from 1 to approximately 1000 CFU ml−1 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 reason for adding molasses is to feed the microbes, so it is important to ask, “Should the gardener 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.

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 in the garden. 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.

References:

1) Photo Source: Йоана Петрова

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Robert Pavlis

I have been gardening my whole life and have a science background. Besides writing and speaking about gardening, I own and operate a 6 acre private garden called Aspen Grove Gardens which now has over 3,000 perennials, grasses, shrubs and trees. Yes--I am a plantaholic!

131 thoughts on “Molasses for Plants”

  1. Today’s chuckle …
    “Molasses contains a huge array of crucial minerals needed for weed plants to survive and thrive. Alongside this massive benefit, it helps bring the soil to life by feeding beneficial bacteria and fungi . This then enables plants to tap in even more nutrients already present in the soil.”

    🤦🏿‍♀️

    Reply
  2. I bought some molasses for horses, so really cheap and decided to give it a try. I chose 12 squash plants and gave 6 of them molasses, about two tables spoons in a couple of gallons of water, and this was split between the plants.
    To my utter amazement within 48 hours they looked considerably better than their neighbours. How could this happen so fast?
    So I chose another 14 zucchini and 6 received the molasses water.
    The second day after 48 hours, I went out in the evening to water them again and noticed that 8 of the plants were drooping in the heat (in the high 80sF all afternoon). But six of the plants were still upright and looking very happy. And yes they were the ones who had the dose of molasses.
    So by the next morning the 6 plants were clearly bigger and stronger than the others.
    So now with another 10 hot days forecast most of the rest have been given some molasses.
    Your arguments against molasses contain no evidence which you demand for people who support it.

    Reply
    • “So by the next morning the 6 plants were clearly bigger and stronger than the others. – that is physically impossible – plants do not grow that quickly no matter what you give them.

      Reply
  3. All the BLAHBLAH doesn’t matter, if you re removing any AG product from its growing medium then you are removing nutrients from the soil, medium etc., so unless you replace it with those elements you removed with say a carrot, then in time you will need to replace it, or get starving food, and lackluster growth, so it doesn’t matter it needs to go back in, I don’t see one post that somebody did a tissue sample to see if a plant has benefited or been stressed by Molasses. every couple of years I pay the $20 per tissue sample and feed my soil accordingly, food tastes better, keeps better and produces more, and less pests too.

    Reply

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