Following on from our “Roots Love Char” post on our Tomato trial we have explored how radish plant roots might also interact with biochar in the soil. This is a small observational experiment.

What we did

We carried out a small radish growing trial over the winter months – beginning November to end February. We grew four trial and four control plants in the same beds that we had used for the tomato growing trial of 2020.

Some of the control plants didn’t receive sufficient water towards the end of the trial so a fair comparison was lost. We did however extract the whole plants from the soil. It was easily apparent that the root balls (roots and soil) were much smaller on the control plants than the trial plants. We photographed them.

We followed the same protocol for examining these roots as we did for the tomato trial, we palpated the soil mass and much soil dropped off without apparent loss of root. We then dunked the root balls into water to gently remove the bulk of the soil. The plants were then laid out to dry.

After drying for few days the roots were carefully teased apart and examined visually. The roots on the trial plants were decorated with particles, mostly black. The control plants had far fewer decorations. Using the pressure from a screwdriver tip many of the particles crushed, with a brittle failure, into small pieces/dust and seemed to be biochar. There were some that crushed into a soft rather than brittle failure, so were probably woody fragments rather than biochar.

It does seem that radish the roots “enthusiastically” engage with and strongly bind to biochar particles. This would seem to lend support to the idea that the plants do gain benefit from their association with biochar.

We are not the only ones to have seen this effect. Prendergast-Miller, Duvall and Sohi have also reported on the relationship between roots and biochar. Quoting from their paper, “The rhizosphere contained more biochar particles than the bulk soil, an indication that roots preferred soil containing biochar particles.”.

Two Control radish plants washed roots showing very few attached particles
Close up of largest Trial radish plant showing large amounts of attached particles, many biochar


Biochar–root interactions are mediated by biochar nutrient content and impacts on soil nutrient availability
M. T. Prendergast-Miller, M. Duvall, S. P. Sohi
European Journal of Soil Science 04 September 2013