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  Riverford sustainable development project


      

growing - the case of hot house tomatoes 

'for every kilo of tomatoes picked 2-3 kilos of CO2 are released into the atmosphere'

 

'Local' is commonly assumed to be best for the environment, but when it comes to heated glasshouse crops this is often not the case. Even with the help of tunnels or glass, without heating tomatoes can only be harvested in this country from July to October. The bulk of the crop is harvested in August and September; a very short season even for the most die-hard seasonal eater.  

 

Intensive, highly professional hot house producers plant their crops in heated greenhouses in January or February so they can harvest from March or April through to November or December.  This produces prolific yields over a long season but only at the expense of huge amounts of heat which is normally produced by burning gas or oil.  For every kilo of tomatoes picked two to three kg of CO2 are released into the atmosphere.

By comparison it is possible to produce tomatoes in the South of Spain or Italy, without heat, right through the winter (though heat is still sometimes used to improve the quality and consistency of the crop). The emissions from transporting those tomatoes to the UK (about 240g CO2 per kg of fruit) are about a tenth of those associated with growing them closer to home using heat.  The situation for peppers which are lower yielding but require the same amount of heat per square meter is even worse at about 4.5kg of CO2 per kg of fruit.  We have not done the calculations for other hot house crops but I would expect the figures for aubergine to be similar to peppers and cucumbers to be lower than tomatoes.

 

We do buy heated glasshouse produce ourselves.  The figures used above are calculated from figures given to us by some of our more efficient suppliers.  There will be some variation depending on the particular system; for some heated but lower yielding systems the situation could be worse, for some growers using very high yielding chemical systems it could be a little better.  The best and most progressive growers are working hard to reduce their energy usage with insulating thermal screens, the use of waste heat from combined heat and power or nearby industry, ground source heat pumps and some are even investigating tapping geothermal heat.  Even with these technologies there is a vast gap between the greenhouse gas emissions associated with hot house production and products grown without heat, even if they travel 4,000 miles by road to get here.

 

In an ideal world we would all eat with our local season and would need neither heated glass nor imports.  Much enthusiasm has recently been professed for this approach, but in  my experience a sneak look into the fridge of even the most vocal proponent will normally uncover out-of-season tomatoes and peppers.  Given this current reality, we need to establish the least damaging option.  In terms of emissions the evidence is that trucking from southern Europe is the best option.  We have tried sea-freight from Morocco (Agadir to Portsmouth)  which is 3 times more CO2 efficient than road transport in terms of emissions, releasing about 110g of CO2 per kg of fruit.  Unfortunately so far the quality of the produce on arrival has been poor.