Volcanic Ash Triples Plant Growth in Study

A UC San Diego greenhouse experiment found that mixing basaltic ash into forest soil changed the microbes around plant roots and boosted growth.

Updated on Nov. 4, 2026 in Botany

Volcanic Ash Triples Plant Growth in Study

Live Poll

Should the U.S. encourage farmers to use volcanic ash to improve poor soil?

Researchers at UC San Diego found that adding 3% basaltic ash to forest soil roughly tripled the biomass of coleus plants over a four-month greenhouse experiment. The ash altered the bacteria and fungi surrounding the roots.

Why it matters

The findings suggest volcanic ash may offer a way to improve depleted soils by reshaping soil microbial communities rather than simply supplying minerals directly to plants. The results point to a possible route for restoring worn-out farmland.

The study was a four-month greenhouse experiment that tested one ornamental plant species and one ash type, with plant biomass roughly tripling compared with untreated soil. It remains untested whether the same effect occurs on working farmland, in other climates, or with food crops.

The players

UC San Diego

The University of California, San Diego is a public research university whose researchers conducted the greenhouse experiment on volcanic ash and soil microbes.

The details

Researchers at UC San Diego mixed 3% basaltic ash into forest soil and planted coleus, then tracked growth and soil microbes. The ash increased beneficial plant growth-promoting bacteria and fungi while decreasing parasitic nematodes, suggesting the effect works through a microbiome shift rather than direct mineral feeding.

2020: A study of Sakurajima volcano ash microbial communities was published in Scientific Reports.
2025: The greenhouse volcanic ash study was published in the journal Ecosphere.
2025: A study on volcanic ash weathering and microbial nutrient cycling was published in the European Journal of Soil Biology.

The Big Picture

The findings build on a 2020 Scientific Reports study of Sakurajima volcano ash and its microbial communities. Together, the work points toward soil microbiology as a mechanism that could explain how volcanic materials may restore depleted agricultural land.

Farmers and gardeners could eventually use volcanic ash as a soil amendment, but the findings are from a controlled greenhouse setting. Practical application would require field trials on working soils before any changes to fertilizer practices.

The takeaway

Soil health may depend as much on the microbial communities living in it as on the minerals it contains. Gardeners and farmers should watch for field-scale results before changing their soil practices.