In 1992, The New York Times reported that “Crop plants sprayed with diluted methanol showed significantly greater yields while requiring less water. Cabbages doubled in size, wheat seeds doubled in weight and number, the water needs of cotton crops dropped by half, tomatoes grew faster and were significantly sweeter, roses grew faster and produced more flowers, and strawberries, eggplants and watermelons gave better yields.”
That was almost 30 years ago. What does science say today, about using methanol on plants?
What is Methanol?
Methanol, also known as methyl alcohol, is a simple chemical found in all life forms and has the formula CH3OH. It should not be confused with the drinking alcohol, ethanol, or rubbing alcohol which is isopropyl alcohol. This post is only talking about methanol.
An older name for it is wood alcohol because it used to be produced by distilling wood. It is used as a solvent and you might have used it as an additive to gasoline. It is available from Amazon.
Plants produce methanol and release it from leaves through stomata, making it one of the major organic compounds in forest air. It is also believed that this leaf methanol supports an abundant population of bacteria which live on the leaves.
It is important to understand that methanol at high concentrations is also toxic to plants. At over 30% it damages some leaves and at 10% it damages roots.
Methanol Foliar Spray Enhances Plant Growth – Early Studies
Research was published in 1992 that showed a methanol foliar spray increased plant growth. That was surprising since methanol is such a simple molecule and it’s produced by plants as a waste product. If true, this could be very significant since methanol is easy and inexpensive to produce. It also has few if any environmental issues since microbes easily break it down.
Part of the scientific method is for others to redo the work so they can verify the results, so there was a flurry of research over the next few years.
A review of all of this work was published in 1996 and it concluded that methanol does not produce a consistent increase in crop yield.
If we go back to the initial study, we find that the researchers never claimed that methanol enhanced the growth of all plants, in all conditions. What they reported was:
- C3 plants (tomato and wheat) showed enhanced growth.
- C4 plants (maize and sorghum) did not show enhanced growth.
- C3 plants only showed enhanced growth when the plants were growing in water-stressed conditions.
- Spraying at night had no effect.
This highlights a common problem when scientific information is transferred to the general public, and sometimes, even among scientists. The results are embellished and simplified for a better story.
What is a C3 and C4 plant? The terms refer to the internal biochemistry and photosynthesis methods used by a plant. C4 plants are more efficient at using water and so they are less affected by low water environments. Most plants are a C3 type.
Methanol Enhances Plant Growth – Later Studies
Research in methanol for plants waned after 1996, but a few new studies did appear. This time they were more focused on water-stressed plants and a second review of these studies was published in 2002. It concluded that methanol did enhance growth of water stressed C3 plants, and it proposed several biochemical explanations for this effect. In simple terms, methanol increases the efficiency of photosynthesis.
A review in 2018 also states that the benefits of methanol are limited to some C3 plants. A study done on rice, a C3 plant, found little effect from foliar methanol spray. This rice was grown in normal flooded fields and was not water-stressed. A study in 2003 used tomato, bean, sugar beet, and oil rapeseed, and found that weekly treatments with methanol resulted in a 20-30% increase in yield, but that additional irrigation produced the same increase in yield.
Methanol shows positive effects on plant growth with some C3 plants but only when these plants are grown in a water-stress environment.
Methanol vs Water in the Garden
I think one title I saw summarizes the use of methanol for plant growth very well; “methanol may revolutionize desert agriculture”. The original study was does in Arizona and repeated work has confirmed that methanol can be useful in areas that don’t have enough water to grow crops properly.
The benefits are limited to C3 plants.
If you have a choice between watering more often or spraying plants with methanol, it is much better to use water. In dry areas, consider using mulch and drip irrigation to reduce water needs. A foliar methanol spray may help in dry locations.
Methanol foliar sprays should be between 10 and 20%, and root drenches are not recommended.
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