The Carbon Footprint of Gardening

The media often gives the impression that all gardening benefits the environment. Surely gardens are always good as plants absorb carbon dioxide (CO₂) and give out oxygen, reducing our net carbon emissions? Surprisingly, it’s not always that simple. There are many inputs to modern gardening methods that need to be questioned as they release significant quantities of greenhouse gases:

• Fertilizer: Almost all synthetic fertilizers that contain nitrogen will have been produced using the Haber Bosch process. This relies on converting the methane from natural gas into hydrogen first and the resulting by-product is CO₂ making commercial fertilizer production a large producer of greenhouse gases. Manure is not much better as composting it releases methane which is itself a very potent greenhouse gas and some people calculate that the resulting carbon emissions are worse than for synthetic fertilizers.
• Peat: Natural peat bogs are one of the earth’s best carbon sinks – they absorb CO₂ from the atmosphere and lock it away. Buying potting soil that contains peat has a negative carbon impact because it removes part of the earth’s ability to absorb greenhouse gases. Amazingly nearly half of all potting soil sold in the UK still contains peat so if it doesn’t say peat-free on the label it probably isn’t!
• Heat: Heating greenhouses is a very inefficient process. There is no double-glazing and they’re draughty because good ventilation is required for plants. Unless you’re using electricity from a wind-turbine to power an electric heater there will be a considerable carbon footprint.
• Water: Food gardening requires large amounts of water especially during hot summers. When that comes from treated drinking water supplies the carbon footprint can be significant. A hosepipe can use 1000 liters per hour and the energy that went into treating and supplying that water is equivalent to leaving a 60W light bulb (or 5 low-energy light bulbs) running for the same period of time.
• Non-renewable Resources: Gardening stores and gardening supply companies often promote their green credentials yet their bottom line is nearly always profit and persuading us to buy ever increasing amounts of hard goods. Everything they sell requires energy to produce, adding to your garden’s carbon footprint.
• Transportation: Although growing food cuts out all the food miles that come from the food superhighway that supplies our grocery stores there are still many garden products that are shipped around the world.

Once you take all these into account it’s easy to see why the kind of easy gardening encouraged by gardening stores could actually end up contributing to a higher carbon footprint, adding to the problem of climate change.

Good-for-the-World Gardening

Plants are so good and so central to our world’s natural balances that in many cases we simply need to live ‘lighter’ on the earth. Here are some possible solutions:

Fertilize with Compost and Green Manures (cover crops): There is now ample evidence that using good organic gardening techniques produces crops that are at least as good as non-organic and much better for our health and world. Composting everything you can reduces the methane emissions that would come from sending it to landfill (it’s estimated that about 25% of all landfill waste in England could have been composted) and increases your gardens growth, a win-win situation. However, to keep methane emissions low, the composting needs to be well aerated so techniques such as hot composting where the pile is regularly turned to mix in air are preferable.
1. Reduce Reliance on Manure: For most food crops manure needs to be well composted before use to eliminate pathogens but this process is what creates methane. Apart from the release of greenhouse gases there are other problems with manure such as aminopyralid herbicides so it’s best to substitute compost and green manures where possible.
2. Avoid Peat: It isn’t easy to find high-quality compost for seeds and young plants since many peat free composts come from composted wood chippings and are too coarse. One solution I have tried is coir-based compost such as Fertile Fibre and I have had excellent results with this for several years. Coir is a waste product from the processing of coconut fibre and it is shipped across the world to reach us. However, this shipping is low on the scale of transport-produced CO₂ and the resulting compost is so much better than alternatives I have tried that I think it’s worthwhile.
3. Supplement Light not Heat: It’s much more efficient to start seedlings inside a heated house with full-spectrum grow-lights than to heat a light but draughty greenhouse. I have now taken to leaving my greenhouse empty over winter and raising seedlings with grow-lights in a bedroom (warm air rises in the house so it’s naturally warm).
4. Use Grey Water: With sensible precautions water from roofs, sinks and baths can be used around the garden rather than treated drinking water.
5. Reduce, Reuse, Recycle: For some excellent tips see our article on Recycling in the Garden where many of our readers have commented about how they use other people’s cast-offs in the garden.

A lot of this has been common practice amongst organic gardeners for some time now. It seems to me that the real challenge is going to be spreading this to the general public. We need people to move away from commercial quick-fix gardening to an awareness of how growing your own organic food can help offset the carbon footprint of our lives. This is what governments really need to encourage if they want a significant reduction in our carbon footprint.