Look after soil

 

After rocks and the ocean, the biggest carbon store is the soil. Climate-friendly gardeners can not only look after soil outside our gardens (for example by using peat-free compost and water-thrifty plants) but within our own gardens as well. That means both protecting the soil that’s there already, and enriching it by encouraging vigorous growth that is then converted to long-term soil carbon or humus.

We can do this in many ways:

• have a garden of plants and soil rather than a garden that’s full of buildings and paving;
• create an orchard garden (or forest garden or woodland garden) with fruit and nut trees, and many layers of vigorous plants below them, to both shelter the soil from sun and wind, and to add organic matter from roots, leaves and twigs;
• plant some deep-rooted plants such as comfrey to increase soil depth;
• plant ground-cover plants to protect the soil and to add organic matter;
• add organic mulch (such as bought woodchip, or chopped garden prunings, or leaves, or garden compost) to protect and add organic matter to the soil, until the ground-cover plants fully cover the soil and can do the job directly;
• choose perennial plants rather than annual plants whenever possible, and avoid cultivation;
• if we do grow annual plants, for example in vegetable plots, make sure the soil is always protected, for example by adding organic mulches and/or sowing green manure plants;
• turn garden and kitchen ‘waste’ into compost, and add it to the soil, especially where we’re taking a harvest, such as in vegetable patches;
• chop up garden prunings and collect leaves and use them for mulch (don’t burn them on bonfires!);
• if we have a lawn, include clover or other nitrogen-fixing plants rather than ‘weed-and-feed’, herbicide and synthetic fertilizer, to encourage vigorous growth but not at the expense of mycorrhizas;
• if we have a lawn, use a mulching mower to feed grass clippings back into the lawn and so increase soil carbon;
• only tread on the soil when it’s moist, not when it’s too wet or too dry, to avoid compacting the soil.

If we want to grow food, the most obvious way to decide what to grow is to choose our favourite foods that cost us the most to buy or which are best eaten when they’re really fresh – for this Climate-Friendly Gardener, for example, that would mean mulberries, walnuts, and runner beans. But we can also consider the climate impact of crops when they’re grown on a large commercial scale rather than in gardens. Big commercial growers may actually be using more sustainable methods than amateur gardeners for some crops, for example greenhouse salad crops like tomatoes. But some crops cause trouble when grown in fields, especially large fields. Root crops such as potatoes and sugar-beet have to be dug out of the soil, so the soil is disturbed when the crop is harvested and there may not be enough time left in the growing season for a new cover to grow and protect the soil before winter, so the soil gets washed away by rain. Greens such as cabbage have short shelf lives and are harvested many times during the year according to demand, and farmers may feel forced to use machinery that damages the soil in wet weather rather than waiting for suitable conditions. So gardeners can help:

• grow food crops in our gardens which might cause soil erosion and damage when they’re grown in big arable fields.

We need more research into soil. For example, the journal Nature Climate Change in July 2014 included a report by Christopher Jones and others titled ‘Recently identified microbial guild mediates soil N₂O sink capacity‘. They say ‘The reduction of N₂O to nitrogen gas by micro-organisms is critical for mitigating its emissions from terrestrial ecosystems, yet the determinants of a soil’s capacity to act as a source or sink for N₂O remain uncertain.’ If we knew more we could do more to look after our soil and therefore our climate.