Molasses malarkey

Yesterday I received this link from a Facebook friend who said “when I read this I thought of you.”  More likely she was thinking of (enjoying?) the mental agony I suffered as I waded through this morass of misinformation. (By the way – those of you who are educators of some sort – this would make a great “how many things are wrong?” question for your students.)

There’s SO much to discuss in this post that I think I’ll split it up into separate posts.  Here’s the first paragraph:

“Cheap, easy and does it all!

“Not your kitchen molasses! That has had the sulfur removed and you need it in there. Horticulture Molasses does things for your plants like nothing else can and it’s the cheapest gardening product per square foot…a gallon can cover a half-acre! Put it in a sprayer, turn some music on and start spraying every inch of your yard, no need to be careful. You simply can’t over do it. Molasses raises the sugar content of plants and kills insects,causes a massive bloom of microbes in the soil and drives out Fire Ants, what more do you need?”

I’d not heard of “horticulture molasses” before, but there are so many new products sneaking into garden centers that I’m not too surprised. Let’s look at some specifics here.

  1. “Kitchen molasses has had the sulfur removed.”  This isn’t quite accurate.  Molasses doesn’t contain sulfur naturally; sulfur dioxide is sometimes added as a preservative during the processing of sugar beets or sugar cane and ends up in molasses.
  2. “Put it in a sprayer…and start spraying every inch of your yard, no need to be careful. You simply can’t overdo it.”  This is some of the most irresponsible advice I’ve ever seen. If this is such a powerful insecticide (as you’ll see later in the post), then OF COURSE you can overdo it.
  3. “Molasses raises the sugar content of plants.”  This bold statement has no basis in reality. Exactly how it is supposed to get inside the plants?  Not through the protective cuticle.  Through the stomata?  Possibly.  But how much sugar could be taken up this way? There are 256 tablespoons in a gallon.  Three tablespoons means that molasses is about 1% of the total volume in a gallon of this mixture (you’ll have to look at the bottom of the linked post to see the recipe).  And since molasses is only about 50% sugar, then a gallon of mixture is about 0.5% sugar. We’re talking about homeopathic levels of sugar here.
  4. “Molasses…kills insects, causes a massive bloom of microbes in the soil and drives out Fire Ants.” The microbe information is more or less correct (maybe not “massive” given the concentration of molasses used).  Microbes love carbohydrates.  The insecticidal claims are nonsense.  And since the next paragraph of the original post addresses this in more detail, I’ll hold off my dissection until my next post.

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Linda Chalker-Scott

Dr. Linda Chalker-Scott has a Ph.D. in Horticulture from Oregon State University and is an ISA certified arborist and an ASCA consulting arborist. She is WSU’s Extension Urban Horticulturist and a Professor in the Department of Horticulture, and holds two affiliate associate professor positions at University of Washington. She conducts research in applied plant and soil sciences, publishing the results in scientific articles and university Extension fact sheets. Linda also is the award-winning author of five books: the horticultural myth-busting The Informed Gardener (2008) and The Informed Gardener Blooms Again (2010) from the University of Washington Press and Sustainable Landscapes and Gardens: Good Science – Practical Application (2009) from GFG Publishing, Inc., and How Plants Work: The Science Behind the Amazing Things Plants Do from Timber Press (2015). Her latest effort is an update of Art Kruckeberg’s Gardening with Native Plants of the Pacific Northwest from UW Press (2019). In 2018 Linda was featured in a video series – The Science of Gardening – produced by The Great Courses. She also is one of the Garden Professors – a group of academic colleagues who educate and entertain through their blog and Facebook pages. Linda’s contribution to gardeners was recognized in 2017 by the Association for Garden Communicators as the first recipient of their Cynthia Westcott Scientific Writing Award. "The Garden Professors" Facebook page - "The Garden Professors" Facebook group - Books:

24 thoughts on “Molasses malarkey”

  1. The only thing I ever thought of in molasses as a food cocktail for plants, was not so much for plants, but for feeding the microbes as you mentioned. I can see no direct benefits of feeding molasses to plants other than indirect. Eventually it will break down by the microbes which may then only help the plant through any available byproducts they may make available to plants. Other than that, I’d never consider this idea.

  2. BTW, your point number one reminds me of the 1970s Unleaded verses Leaded Gasoline. Remember how much more unleaded was at the pumps ? Gas was always naturally unleaded. To have leaded gas they had to use additives. People with older model cars that required leaded had to use additives. This was funny. Companies make big money off ignorance.

  3. Oh, man! I was all set to pull out my two gallon sprayer, fill it up with molasses, turn on the radio, and dance my way through the garden, covering it with sticky goo. Guess I’ll have to find another way to have fun.

  4. Kinda gives a new ring to the concept of sweet soil. Can’t wait for the maple syrup season… that stuff ought to be twice as good…. and twice as organic.

  5. I like the bit about it making your yard smell great. Yep, I’m gonna get me some molasses and spray the heck out the property where I’m employed. Then, whenever somebody gets out of their car, they’ll say, “oooh, what is that lovely smell?” Yes, I do believe that will be an excellent use of my time! Oh, it is so hard to not leave a cynical comment on that article. I’m looking forward to hearing the science behind the refuting!

  6. The amount of sulphur in molasses makes this a hugely non-efficient method of applying sulphur. Why not apply sulphur dust or a sulphate fertilizer? I don’t think I’ve seen anything quite so stupid suggested before as a garden application.

  7. Like you, Linda, I’d not heard of horticulture molasses but it sounded so good I wondered if it would be finding its way into our plant clinic advice soon so I did a Google search. There were over 5,000 hits, mostly from folks selling it. They all sounded really good. But my personal favorite was the site touting it for nutgrass control. “This simple technique fires up the microbes in the soil and the nutgrass simply fades away…. As opposed to toxic chemicals, it makes the soil heathlier with every application.” Nutsedge is one of my personal problems and who wouldn’t want healthier soil? And nutsedge control is a common plant clinic question, so anything that works that well, healthy soils and with no environmental concerns…hey, that’s for me! Unfortunately, as a trained skeptical I always need at least a good rationale for how and why it works. I just can’t come up with anything logical for this one.

    But still I was hopeful. So I went to Google Advanced Search in the .edu domains. There were only two hits. One suggests using it as part of a bran/molasses/BTK bait for cutworm control – OK, I can sorta see that. The other was part of a news story out of Baylor where they’re composting their cafeteria waste and horticultural molasses and seaweed extract are additives to the composting operation. It didn’t say why it needed the additives to make compost. Guess that could be another GP post.

    Guess I’ll keep my molasses for cookies.

    1. Bob, I’ve never seen anything make nutsedge “fade away” other than pulling the darn things up and letting them bake on the driveway.

  8. If molasses is bad, or not as good, then why do so many golf courses use it?
    In reference to the Western Fertilizer Handbook, “Sulfer has no characteristic action on the soil except to contribute to the total salt content.”
    Why is this recommended?

    1. Bob, I’m not sure why golf courses use molasses. You should ask them. It’s certainly not recommended by our turf specialist at WSU, who works closely with the golf course superintendents association.

      I don’t know why the blogger I quoted says you need sulfur. I guess you would have to ask her. (Just as an aside, sulfur itself does not contribute to salt content, but it can lower soil pH.)

      1. I use molasses on the lawn and have for a few years. While mere observation doesn’t meet the standards of rigor requisite to sound science, perhaps my observations and unsubstantiated theories as to why I am seeing it would be good food for thought.

        First, I always mulch when I mow and around this time of year (late march, north Texas, Bermuda lawn). I ‘scalp’ as low as I can with the mower then go at the low spots (longer grass) with the seedeater and now again with a very sharp blade to turn that thatch into powder as best I can. As an aside, doing so lets you see depressions and bumps clearly so I can fill holes and hit bumps with a pressure spray attachment on my hose to level and break up soil for more even mowing.

        Back to molasses… I find that the pulverized thatch breaks down much more quickly after spraying molasses (1 cup in a 2gal sprayer). This makes sense based on the general agreement that microbes will bloom to attack the sugar now soaked into the mulched thatch. I got half the yard done a couple years back before darkness intervened and meant to finish the next day but feces occurs and two weeks later I still hadn’t. The molasses soaked section was dramatically greener while the untreated half was just starting to come back.

        Hypothesis: as pointed out, a cup of molasses doesn’t have a whole helluvalot of nutrients when spread over 2000sqft. However, that half inch deep layer of powdered thatch mulch would make for maybe 3 large contractor bags of dried grass particles and presumably contains all the micronutrients applied or absorbed last year and since the treated side now had 1/3 the “mulch depth” of the untreated side that makes sense. I also considered that when you mix the molasses with all that nice rich carbon composting material the ground was getting a “heat blanket” during the early growth season and presumably warmer soil means faster return from winter dormancy. I’ve always thought it somewhat ridiculous that people bag clippings and send them to the dump year after year since one would expect that rich green grass clippings contain all the micronutrients needed to grow rich green grass or is that too logical? Ten years of disposing of a couple bags of clippings every week during the growing season seems like a great way to create a deficit of whichever essential nutrients are in shortest supply.

        In season: I use the same cocktail in summer time and have noted a demonstrable improvement in growth/color/density within a week or two (after the next rain). Again this could be rapid breakdown/recycling of clippings and perhaps a little extra acidity releasing more nutrients into solution in our alkaline soils?

        Two final benefits – I don’t go to much trouble to “perfume” my lawn but I use a lot of mil organize and chicken poop fert. which smell like what they are. A bit of molasses sprayed after application does seem to neutralize it. Presumably that is equal parts masking and accelerated breakdown of the poop. Related benefit: after some bionics to repair a bad lower back I am not inclined to scoop the gifts my beloved cavalier spaniels leave in the yard. If you hit it with a hard stream of molasses water from the sprayer it breaks down much more quickly with less odor and fewer flies. A booming microbial environment seems to have plenty of nice benefits.

        Pure conjecture on my part as to the mechanisms by which molasses improves a lawn but sometimes knowing that something works is sufficient.

        Last thought: molasses killing but grass? Bull manure! Those cockroaches that survive a nuclear holocaust will be dining on nutsedge! The only organic cure I’ve found for that stuff is consistently pulling it by hand over the course of one season on an almost daily basis so it expends all of its stored energy popping up new spikes that I pull in the morning before they green up and start storing surplus energy 😉

        1. Wow autocorrect on iPad made that last post of mine a mess! Nutgrass, not ‘ but grass’,
          Weadeater, not seed eater etcetera
          Milorganite not mil organize.

          Auto obfuscate strikes again!

        2. Despite all the scientific evidence provided here, here are the facts from an old Texas boy and St. Augustine grass owner. When we bought this house there was some Horticulture Molasses in the garage, asking the previous owner what is was she explained she used it on the grass, which was pretty exceptional at the time. I read an article similar to this one and thought B.S., but after the Texas summer hit and grass started looking kind of sickly, I thought well, it can’t hurt, this after feeling like I owned half of the Scott’s company if you know what I mean. Long story made short, I tried this stuff, it worked great, and I continue to use it. Just the facts Ma’am. It works, I’m happy.

  9. Linda, I hear alot of talk about fertilizer and the use of for plants. The University of Wisconsin states that a plant is 45% Carbon, 45% Oxygen and 6% Hydrogen.Is this true and do you have any documentation you could send to me? Second, why do we fertilize if the plant only needs 4% macro or micro nutrients. Unless you are usind distilled water isnt there nutrients available? Wouldnt a water test confirm this information?

    1. Bobby, I’m going to refer you to a government website on plant nutrient content: Though it’s meant for kids it does a nice job of answering your questions quickly and without a lot of extraneous information. Just scroll down to the section on “mineral nutrients.”

      (As an aside, water alone does not contain much in the way of mineral nutrition. Some mineral waters contain calcium, magnesium, etc., but you’re not going to find a lot of nitrogen, which is always in short supply during rapid plant growth.)

  10. As a former plant scientist, I have used molasses as part of an integrated program to help apple trees recover from replant syndrome. And it worked for several growers. I didn’t use sulfur-removed molasses. The program included added microbes and needed micronutrients. Soils were tested prior to the addition of all componenets to assure the proper proportion. I believe that the added microbial activity helps increase the availability of micronutrients to the plants. Molasses is not a silver bullet, but I believe it is a necessary component of an integrated program to help establish plants in poor soils.

    1. Randy, I’m sure as a former plant scientist you must know that university Extension specialists can’t recommend anything that’s not been vetted through peer-reviewed science. That’s why molasses is not part of any university-based IPM program: there’s no science behind its use.

  11. Wow, I’m sorry I didn’t see this when it was posted. You have probably all tossed the idea by now. Its called “horticultural” molasses to stop people from eating it. It is not food grade and may be contaminated with things that are not a part of the human diet.
    It works by providing readily available sugar for natural bacteria. It disturbs the balance of micro-organisms which favoured the growth of the nutsedge in the first place, effects soil amelioration and reduces water logging (which is perfect for nutsedge). It is not a herbicide but it does help.
    The other shocking statement was that molasses may not enter through the cuticle. This is exactly how most sprayed targets enter the plant – by becoming slowly dissolved in the cuticle, and being absorbed by the plant. Use of wetting agents and sometimes spreaders help with the dissolution of the sprayed substance in the cuticle and enhances the uptake.
    It is a frustrating myth that everything is absorbed through stomata. Any entry via the stomata is incidental. They are microscopic openings for air exchange, and getting any spray to specifically use stomata would be extremely inefficient. There are more stomata on the underside of the leaf making them even more difficult to target.

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