QotW: Do home-grown tomatoes produce less CO2?

Now, I am a terrible gardener and can just about keep a houseplant alive, but somewhat controversially, tomatoes are my favourite food of all time. I reached out to Doctor Samarthia Thankappan, from the department of Environment and Geography, University of York, to find out the answer to this question and whether I need to up my horticultural skills.

Samarthia - For most foods, significant greenhouse gas emissions result from land use change which involves above ground changes in biomass, below ground changes in soil carbon, and from the processes at the farm stage, which include the application of fertilisers and pesticides. The combined land use and farm stage emissions account for more than 80% of the footprint for most foods.

Julia - 80%?! That is a huge proportion.

Samarthia - Transport, retail, and packaging account for a small share of the total footprint. 

Julia - Tomatoes like to grow in warm and sunny conditions, which in the UK are few and far between for most of the year. This means in the colder months, our supermarkets are stocked with tomatoes imported from countries with warmer climates. 

Samarthia - In the case of tomatoes, the production system or how the tomatoes are grown is important. Out-of-season tomatoes grown under heated greenhouses add significantly to greenhouse gas emissions, and this contribution typically overshadows the carbon footprint of tomatoes imported from long distances from warmer production regions. This means locally produced tomatoes grown in greenhouses in colder seasons will have a higher carbon footprint than field-grown tomatoes shipped from long distances.

Julia - So, with all that information in mind…

Samarthia - The lowest carbon footprint would be for those tomatoes grown in a grow bag in your garden (assuming you have not placed the grow bag in a heated greenhouse!) compared to the ones bought from the supermarket.

Julia - Overall, if you are growing your tomatoes on your window ledge, in a greenhouse or out in the garden without help from a energy-guzzling greenhouse lamp, the footprint on those tomatoes should be smaller than the packets you can pick up at the supermarket. Which means I definitely need to up my green finger game. Thank you to Jodie for your question and to Dr Samarthia Thankappan for weeding out the truth for us. Next week, we have got a question which is out of this world from Matt.

Matt - Early commercial flights were scheduled and had air traffic control but pilots were allowed a fair amount of latitude to deviate off course ,which caused some mid air collisions. With three space missions currently converging on Mars how do the nations avoid orbital collisions? Do they share data? Do they have transponders? Thank you.