One, five and fifteen day inoculated biochar-compost seed germination trial

September 2020

biochar inoculation trial


Total no of individual plants
Total no of types of biochar-compost inoculations

The trial

Treatment of biochar before use seems to be essential to ensure biochar delivers its boost to plant growth. We call this process inoculation. Gardeners use many recipes for inoculating biochar. These all involve nutrient rich moist media or solutions of nutrients. Many biochar users keep the biochar in contact with the media for some time and 14 days is the standard.

We thought it would be handy to check out the effect of shorter treatment periods. Would we see good germination and growth performance?

Using the cabbage trials <> as a basis we set up trials with our three test biochars as for the cabbage trial. We did tests in parallel with biochar concentrations at 9 and 2%. The plants chosen were Cabbage, Winter Jewel F1, Calendula, “Pot Marigold” Nova and Carrot, Early Nantes 2 – Frubund. Small six-cell (7.5×5.5 cm) seed trays provided our growth station. We planted 2 cabbage, 2 calendula and 2 carrots per cell, cosy close packing.

We made stock mixtures of the biochars with compost. The first seed tray received its mixture after one day of inoculation. We planted it up the above seed combination for each of the cells, a total of 36 seeds per tray.

We repeated this after five then fifteen days of inoculation.

Over the following weeks we monitored the germination rate.

The results

At the end of the trial the overall germination rate was 77%. For the more concentrated biochar mix we achieved a germination rate of 86% vs 69% for the weaker (2%) mix.

The surprising thing was, we did not see so much variation for different inoculation periods. The average germination rate for 1 and 5 day inoculation was 81% and 81%. For the 15 day period it was less at 70% and this latter result excluded one cell that had only a single germination, we deemed it an outlier.

The conclusion

It would appear that mixing a higher concentration of biochar into the compost in this trial led to a more successful germination rate, but that a longer inoculation time appeared to have a small negative effect on seed germination. This small scale test is just that we do not draw wider conclusions.

Our other trials include – Marmande Superprecoce tomatoes and Winter cabbages