Hort2thefuture project partner, European training Academy (EUTA), with the leadership of Steve Quarrie, has been working with growers in Serbia and North Macedonia on assessing soil microbial activity using the teabag test.
In essence, the test involves weighing a teabag, burying it in the soil for several months, then digging it up, cleaning, drying, and reweighing it. The weight loss during this period serves as a measure of the soil’s microbial activity. Its simplicity has garnered widespread interest among growers.
Finetuning the approach
Initially, the methodology relied on non-biodegradable teabags, meaning the bag itself did not lose weight. However, teabag manufacturers are now using various types of biodegradable teabags, made from materials such as modified starches or biodegradable plastics. While some manufacturers disclose the composition of their biodegradable teabags, they understandably don’t specify how quickly their teabags degrade when buried in soil.
To address this, Steve Quarrie is currently testing the degradation rate of several teabag brands in a trial in his back garden. Four brands of green tea in pyramidal teabags (which are recommended for the teabag test) are currently buried approximately 12 cm deep in a row. They will be unearthed after one and two months to assess how well the teabag itself withstands the soil environment.
Selecting a suitable green tea teabag has revealed variations in several other factors: there’s significant variation among brands in the weight of the teabag, whether teabags have a tag attached (as shown in the right-hand image), considerable differences in the size of the tea leaves inside the bag (whole leaves or crushed fragments), and a wide range in the colour of “green” tea leaves, from actual green to black.
Choosing a teabag with an attached tag makes it easier to locate where the teabag has been buried, and a replicate number can be easily added. It remains to be seen whether whole leaves or crushed leaves make a difference in the speed of degradation.
A recommendation on the choice of brand and specific teabag to use will be available sometime in autumn 2025.