If you were going to grow tomatoes this year, why not get involved in our biochar trial and potentially increase your yield...

marmande superprecoce tomatoes ripening

The goal

We have conducted our own small scale tomato trials and recorded significant yield increases of 49% in 2020, 32% in 2021 and 32% in 2022. However this is a very small pool of data and so we would like to collect data from other UK gardeners who are interested in participating in the same experiment, leveraging the power of the collective.

Our goal is to measure the effectiveness of a biochar activated compost against a compost control as a medium for growing tomatoes by recording tomato crop yield (inc weight and fruit number) in this 2023 growing season.

Limited places available

Total no of individual participants
Total no of individual plants

What we will do

If you sign up to participate, we will:

Deliver you a free small box of biochar via post for your trial

Provide a simple digital data collection tool via this site 

Publish the results after the growing season ends

What you'll need to buy/have

Gardening tools – trowel/spade/wheelbarrow

Garden compost or 2 x compost bags

6 x tomato plants (If you are growing from seed, you’ll need the seeds, small pots and starter compost)


Kitchen scales

Step 1 - Choose how you'll conduct your experiment

Set up

We know that you all have different setups at home or on your allotment and so we want to make this trial fit in with how you do things.

As such you can use plots, grow bags or pots.

Tomato variety

Everyone likes different tomato varieties, so choose the variety you’d like to try. It’s important that all 6 plants are the same variety.

Start growing your 6 tomato plants, as soon as possible so they will be ready to plant out in May. Alternatively in May go out and buy 6 healthy tomato plants of the same variety at your local garden centre or online.

Step 2 - Mix biochar with your compost (March-April)

Raw biochar needs to be activated before you grow plants in it otherwise it will take nutrients away from the plant rather than make them available.

Once you have received your biochar in the post from us, open it up and mix it with one of your compost bags or mix it with half of your garden compost if you’re growing in plots. As shown in the photo using a wheelbarrow to do your mixing is ideal.

This will need to activate the biochar for at least 4 weeks, before starting the trial.

Note: If you use your own compost, you’ll need to measure out how much you’ll need for either 1 plot or 3 pots. Using grow bags means you don’t need to worry about volumes.



preparing biochar compost mix

Step 3 - Planting out (May)

When the risk of frost has passed, its time to plant your tomato plants out

Take 3 of your tomato plants and plant them in your control compost and plant the other 3 in your biochar amended trial compost.

If you are lucky enough to have a cold frame/greenhouse you could plant out earlier than May, but you need to make sure that you have given your biochar amended compost at least 4 weeks to manure before doing so.



tomato seedlings

Step 4 - Measurement and data collection (June/October)

Tomatoes of course ripen at different times, so the best way to undertake this step is to observe when you have a suitable ripe crop on both your control and trial plants. Pick from control plants and record how many you have picked and their combined weight, then pick from the trial and measure those. Go to the website and fill in the date, number picked, combined weight and whether they were from the control of biochar trial plants. We will send you the website link when it is ready.

Repeat this throughout the season as more tomatoes ripen.

tomato harvesting

Points to note

Treat your control and trial in exactly the same way, i.e. water and fertiliser with the same quantities throughout the season

Compost quantities:

We appreciate that your plot, grow bag or pot may be slightly different in size to what we have mentioned above. As such we just ask that when you record the data you just tell us which setup sizes you have, so we can take that into account.

The higher the volume of compost you use will mean the % of biochar used in your mix will be less, we are aiming for around 10% biochar to the compost.

Building on previous work

This trial is inspired from work that start over a decade ago and has taken a few forms.

The Big Biochar Experiment (2012) – Run by Cécile Girardin from University of Oxford 

The Biochar Experiment (2014/2015) – Run by Donna Udall from the University of Coventry

Join the big tomato trial

Places are limited, as we only have 100 free biochar boxes available.