# Molasses and sugars for cannabis: microbe food, not plant food

> Molasses and other sugars feed microbes, not the cannabis plant. Plants make their own sugars by photosynthesis in the leaves and send them down to the roots; roots don't take up meaningful sugar from the soil, and microbes eat added sugar within days. In living soil a little molasses can wake up microbes, but there's no evidence it raises yield, potency or sweetness. In sterile hydro it's not needed and can feed the bacteria that cause root rot.

- Canonical: https://genetixbay.com/knowledge/nutrients/molasses-and-sugars.html
- Category: Nutrients · Level: Beginner
- Evidence: Supported · Status: Draft: awaiting expert review
- Stage: Veg, Flower · Systems: Any system
- Updated: 2026-11-02 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)"

## Questions and answers

**Does [molasses](https://genetixbay.com/knowledge/glossary/molasses.md) help cannabis?** Molasses helps the microbes in the [root zone](https://genetixbay.com/knowledge/glossary/root-zone.md), not the cannabis plant directly. Plants make their own sugars by [photosynthesis](https://genetixbay.com/knowledge/glossary/photosynthesis.md), and microbes eat added sugar within days. In [living soil](https://genetixbay.com/knowledge/glossary/living-soil.md) a little molasses can stimulate microbial activity, but no controlled study shows it raises cannabis yield, potency or flavour. GenetixBay's position: molasses feeds microbes only, and isn't needed in sterile hydro.

**Does molasses make buds sweeter?** No. Cannabis aroma and flavour come from [terpenes](https://genetixbay.com/knowledge/glossary/terpene.md) and other compounds made in the [trichomes](https://genetixbay.com/knowledge/glossary/trichome.md), built from the plant's own photosynthesis. Sugar poured into the soil is eaten by microbes; there's no controlled evidence it changes the taste of the flower. Sweetness in the smoke comes from genetics, a healthy plant, and a good dry and cure.

**Can I use molasses in hydro or [DWC](https://genetixbay.com/knowledge/glossary/dwc.md)?** It's not needed and it's risky. In a sterile or clean hydro system, sugar in the reservoir feeds bacteria and fungi, which use up dissolved oxygen and can form slime on the roots, the conditions [Pythium root rot](https://genetixbay.com/knowledge/glossary/pythium.md) likes. Plants make their own sugars. If you run a [beneficial-microbe reservoir](https://genetixbay.com/knowledge/glossary/beneficial-microbe-reservoir.md), feed it with products made for that, not kitchen sugar.

**Can plant roots absorb sugar?** Roots can take up some sugars in sterile lab conditions, which is why plant tissue-culture media contain sucrose, but in a pot or reservoir microbes eat added sugar long before the plant could use it in any meaningful amount. A growing cannabis plant gets its sugar from photosynthesis in its own leaves, moved to the roots and flowers through the [phloem](https://genetixbay.com/knowledge/glossary/phloem.md).

**Does molasses add nutrients?** Molasses, especially blackstrap, contains some potassium, calcium, magnesium and iron, but in amounts that are small next to a proper feed. Its main effect in soil is as a quick carbon source for microbes. If a plant needs potassium or magnesium, a balanced fertiliser supplies them far more precisely than molasses.

**Short answer, in plain words.** A cannabis plant makes its own sugar. Its leaves turn light, air and water into sugar, then send it down to the roots and up to the buds [1]. Sugar you pour into the pot doesn't go into the plant; the **microbes** in the soil eat it within days [2]. In living soil that can wake the microbes up, which is fine. In clean hydro it isn't needed, and it can feed the wrong bugs. GenetixBay's position: **molasses and sugars feed microbes only, not the plant** (founder's field experience) [6].

> **Greenleaf says:** Your plant is a sugar factory with a solar roof. It doesn't need a spoonful of molasses; your soil microbes might.

## Where does a cannabis plant get its sugar?

From its own leaves. Photosynthesis in the chloroplasts builds sugars from CO₂ and water using light energy, and the phloem carries them to roots, new growth and flowers [1]. *Established.*

**Where a plant's sugar really comes from.** Light → Leaves make sugar: CO₂ + water + light → sugars → Phloem carries it: To roots, shoots and buds → Roots and buds grow. Source: [1]

*Chloe: Chloe, a chloroplast, catching light: this is where the plant's sugar is made.*

## What happens to sugar poured into the pot?

Microbes eat it. Sugar is the easiest food a soil microbe can find; adding fresh, easily used carbon sets off a burst of microbial growth and activity, sometimes speeding up the breakdown of older organic matter too (a "priming effect") [2]. *Established (soil biology).*

Roots can absorb some sugars, which is why sterile plant tissue-culture media include sucrose [3]. In a pot or reservoir full of microbes, though, there's no evidence that cannabis takes up meaningful sugar from the root zone. *Supported.*

## Does molasses make buds sweeter or bigger?

No evidence says so. *Supported.*

- **Flavour and aroma** come mostly from terpenes made in the glandular trichomes from the plant's own carbon [4]. Sugar in the soil isn't on that path.
- **Yield and potency:** we found no controlled cannabis study showing molasses raises either.
- **Nutrients:** molasses carries some potassium, calcium, magnesium and iron, but far less precisely than a balanced feed.

## Living soil vs hydro

**Molasses in living soil vs in hydro**
- **Living soil** (Microbes are the point)
  - Pro: Quick carbon for soil microbes
  - Pro: Can boost microbial activity for a short time
  - Con: No proven yield, potency or taste gain
  - Con: Easy to overdo: sour smell, [fungus gnats](https://genetixbay.com/knowledge/glossary/fungus-gnat.md)
- **Sterile or clean hydro** (DWC, [RDWC](https://genetixbay.com/knowledge/glossary/rdwc.md), [NFT](https://genetixbay.com/knowledge/glossary/nft.md), [rockwool](https://genetixbay.com/knowledge/glossary/rockwool.md))
  - Con: Not needed: the plant makes its own sugar
  - Con: Feeds bacteria and biofilm in the reservoir
  - Con: Bacteria use up dissolved oxygen around the roots
  - Con: Conditions Pythium root rot likes

In hydro, [root rot](https://genetixbay.com/knowledge/glossary/root-rot.md) from Pythium and Fusarium is a real problem for cannabis [5]; feeding sugar into the water feeds microbial growth that competes with roots for oxygen. If you run a beneficial-microbe reservoir (a house-endorsed choice), use products made for it (see [bottled microbes](https://genetixbay.com/knowledge/diseases/bottled-microbes-tier-list.md)).

## Common mistakes

- Adding molasses to a hydro reservoir "for the plant".
- Expecting sweeter smoke from sugar in the soil.
- Brewing [compost tea](https://genetixbay.com/knowledge/glossary/compost-tea.md) with molasses and spraying it on plants (it can grow human pathogens; see [does compost tea work?](https://genetixbay.com/knowledge/answers/does-compost-tea-work.md)).
- Using molasses instead of fixing a real potassium or magnesium shortfall.

## Sources

1. Taiz L, Zeiger E, Møller IM, Murphy A. 2015. Plant Physiology and Development, 6th ed. (photosynthesis and phloem transport of sugars). Sinauer Associates.
2. Kuzyakov Y. 2010. Priming effects: interactions between living and dead organic matter. Soil Biology and Biochemistry 42(9):1363-1371. https://doi.org/10.1016/j.soilbio.2010.04.003
3. Murashige T, Skoog F. 1962. A revised medium for rapid growth and bio assays with tobacco tissue cultures. Physiologia Plantarum 15(3):473-497. https://doi.org/10.1111/j.1399-3054.1962.tb08052.x
4. Booth JK, Bohlmann J. 2019. Terpenes in Cannabis sativa: from plant genome to humans. Plant Science 284:67-72. https://doi.org/10.1016/j.plantsci.2019.03.022
5. Punja ZK, Rodriguez G. 2018. Fusarium and Pythium species infecting roots of hydroponically grown marijuana (Cannabis sativa L.) plants. Canadian Journal of Plant Pathology 40(4):498-513. https://doi.org/10.1080/07060661.2018.1535466
6. GenetixBay founder. Field experience (first-hand account; GenetixBay house position).