Does molasses for plants actually work? Molasses for plants is microbe food, not fertilizer. It is mainly sugar with small amounts of calcium, magnesium, iron and manganese. NC State Extension found no research supporting it as a fertilizer, and WSU’s Linda Chalker-Scott calls the sugar uptake claims baseless. Soil microbes do eat it, but plant benefits are unproven.
Key takeaway: Molasses feeds microbes, supplies only trace minerals, has no proven fertilizer value and does not belong in a hydroponic reservoir.
| Claim | What sources say | Verdict | Source |
|---|---|---|---|
| It fertilizes plants | No research-based support found | Unproven | NC State Extension |
| It raises plant sugar | No basis; sugar cannot enter through the cuticle in useful amounts | False | WSU Garden Professors |
| It feeds soil microbes | Microbes consume sugars for energy | True, with mixed effects | WSU Garden Professors |
| It kills insects | Insecticidal claims are nonsense | False | WSU Garden Professors |
What Is in Molasses for Plants?
Mostly sugar. Molasses for plants starts as a byproduct of refining sugarcane or sugar beets. An Ask Extension expert notes blackstrap molasses contains vitamin B6 plus calcium, magnesium, iron and manganese, with no measured, labeled amounts like a fertilizer. NC State’s Gene Fox explains that blackstrap is the dark, thick liquid left when no more sugar can be extracted economically.
Is Molasses for Plants a Real Fertilizer?
No. NC State Extension agent Gene Fox reviewed molasses fertilizer recipes and foliar sprays and wrote that he found no research-based information supporting molasses in any formulation as a fertilizer. The Ask Extension expert found only one 1957 paper on the topic and recommended tested organic or mineral fertilizers whose nutrient contents are measured and labeled.
For measured organic feeding, see our guide to organic bioponic nutrients.
Does Molasses Raise Sugar Content in Plants?
No. Linda Chalker-Scott of Washington State University says this claim has no basis in reality. Sugar cannot pass through the protective cuticle, and little would enter stomata. A typical recipe of 3 tablespoons (45 mL) in 1 gallon (3.8 L) is about 1% molasses, or roughly 0.5% sugar, since molasses is only about half sugar.
Does Molasses Feed Soil Microbes?
Yes, but results vary. Chalker-Scott agrees microbes consume sugars for energy. She adds that, depending on the microbial population, this can have positive, negative or no effect on plants, and no clear field benefit has been shown. NC State notes dry molasses pellets, made by spraying molasses onto corn or soybean meal, are marketed as soil amendments without research support.
Our composting for beginners guide covers proven ways to build soil biology.
How Do Farmers Use Molasses in Research?
As a carbon source. A USDA-ARS and University of Florida study tested anaerobic soil disinfestation, where soil is amended with composted broiler litter and molasses, saturated and tarped for three weeks to suppress pathogens and weeds. Molasses rates above the standard kept the soil acidic, and the standard rate gave plant vigor similar to no molasses.
Is Horticultural Molasses Different From Kitchen Molasses?
Mostly in grade and marketing. Chalker-Scott notes that molasses has no natural sulfur; sulfur dioxide is sometimes added as a preservative during processing, so claims that kitchen molasses had its sulfur removed are inaccurate. NC State explains that sulfured molasses has had sulfur dioxide added, while unsulfured molasses is more common and contains less sulfur.
Why Do Gardeners Believe Molasses for Plants Works?
Visible microbe activity and strong marketing. NC State notes molasses is sold in liquid recipes mixed with organic fertilizers, so any response may come from those fertilizers instead. Chalker-Scott adds that Extension specialists cannot recommend products without peer-reviewed support, which is why molasses is absent from university pest management programs.
Should You Add Molasses to Hydroponics?
We advise against it. No source we reviewed supports molasses for plants grown in water, and Chalker-Scott notes sugars are microbe food. In a closed reservoir, that food is not removed, so we treat it as a cleanliness risk. If you want biology in the root zone, use products designed for hydroponics.
Compare options in our guide to beneficial bacteria and enzymes.
How Should You Use Molasses for Plants in Soil?
Sparingly, as an experiment. If you try molasses for plants in soil, treat it as a side test and keep feeding a soil-test-based fertilizer.
- Test soil first and fertilize from the results.
- Use unsulfured molasses at low dilution.
- Treat one bed and leave one untreated.
- Compare growth over a full season.
- Stop if pests, mold or odor increase.
FAQ About Molasses for Plants
Does molasses kill fire ants?
Chalker-Scott calls the insecticidal claims nonsense, and molasses is used as an ant bait.
Is sulfured molasses better for plants?
Chalker-Scott notes molasses has no natural sulfur; sulfur dioxide is a preservative.
Can molasses replace fertilizer?
No. NC State found no research support for it as a fertilizer.
Can molasses lower soil pH?
In the USDA-ARS study, high rates kept soil acidic.
What about compost tea with molasses?
See our compost tea for hydroponics guide.
Sources
- N.C. Cooperative Extension, Gene Fox — Molasses or Malarkey?
- Washington State University, Linda Chalker-Scott — Molasses Malarkey, The Garden Professors
- USDA Agricultural Research Service — Effect of Molasses in Anaerobic Soil Disinfestation
- Ask Extension — Molasses in the Garden
- Photo credits (Wikimedia Commons, edited with titles): Blackstrapmolasses by Badagnani (CC BY 3.0); Harvesting sugarcane 1 by Danjuma Anthony (CC BY-SA 4.0); Würfelzucker — 2018 — 3564 by Dietmar Rabich (CC BY-SA 4.0); Worm composting 2 by Quadell (CC BY 3.0)