Compost Magazine

Composting tips, advice and science.

Wood ash in a fire.

Ash Can Improve Your Compost Says New Study

13th Feb 2022

Some gardeners caution against using ash in their gardens, but recent (2022) research suggests that ash may actually be beneficial for composters. 

The large-scale experiment conducted in Prague found that adding ash from combusted biomass to compost can increase the total nutrient content of the compost. 

The experiment used a mixture of biodegradable waste, digestate, and straw to prepare the compost. The ash was then added to the compost in concentrations ranging from 0% to 9%. 

The study found that ash increased the nutrient levels of calcium, magnesium, potassium, phosphorus, and sulfur.

However, with increasing concentrations of the ash mixture, the availability of phosphorus, potassium, and magnesium to plants started to decrease. 

Despite this, the desired chemical and physical properties of the composts were still achieved, even with the highest dosage of ash addition. 

The researchers also found that all hazardous materials in the compost were within legal limits. 

This is not the first study to look at the use of biomass ash in compost.

A 2017 study found that biomass ash could more than double the humification levels of compost and increase the levels of calcium, potassium, magnesium, and phosphorus. 

It also found that biomass ash could increase the biological stability of compost. 

The results of these studies are encouraging and suggest that biomass ash can be a beneficial additive to compost. 

It’s important to note, however, that the first study showed that increasing concentrations of the ash mixture can have a detrimental effect on the availability of certain nutrients to plants. High levels of ash may have other negative effects, such as raising the pH of the compost too far.

The studies also focussed on specific types of ash. Different ashes can have different properties, and ashes from some sources can contain higher levels of heavy metals.

Still, ash can be a great addition to compost, provided the right ash is used in the right amount. See our guide to using ash in compost for more guidance on the amount and type to use.


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