We used three biochars. We made one from wood fragments sieved out of garden compost. The second, we made from the compost itself and the third was a commercial biochar. We mixed each separately, 1:10 by weight, with sieved (6.5mm) garden compost.
Once these plants reached about 18cm tall we planted them out into the first two test beds. Bed one was divided into quadrants and the soils in each of the four beds matched the soils in the pots except the compost component was mixed 50:50 by volume with sieved garden soil. The fourth plot for the control plants was a 50:50 vol mix of compost and garden soil