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It starts with the soil

We take a closer look at the increasingly popular 'no dig' method.

Textbook gardening and farming methods are under increasing challenge as the world looks for ways to lock up carbon and produce food sustainably. Often ancient and traditional techniques are being re-examined to see if they can be adapted for large (or small) scale food production.

Double digging has been considered good practice for generations, especially in the vegetable garden. Here a trench is dug, and spade’s depth of soil is removed, the soil at the bottom of the trench is forked over and organic matter added, and the top layer of soil replaced so in effect the soil is worked and aerated for two spade depths. It is recommended for heavy or compacted soils, where a good depth of topsoil is required (e.g. for asparagus) or in cultivating virgin ground. It is done in winter so frost can help to break down clods of earth. However, recently, ‘no-dig’ is gathering momentum as a completely opposite way of managing soil. The principle here is that the soil remains undisturbed allowing a biosphere of worms, insects and microorganisms to establish, which in turn builds a good soil structure which holds air and water, and nurtures beneficial fungi. This provides an environment in which the roots of food crops can establish quickly and thrive. It is a tempting proposition in terms of work, but depends on having a generous supply of organic matter to dress the soil surface annually to a depth of 5-10 cm. Once established no-dig beds are extremely productive and relatively disease free even without crop rotation. Deep-rooted perennial weeds must be removed when the beds are first made, either by repeated pulling out, or by smothering with compost and cardboard, or digging out as a last resort. Weedlings can be pulled out as they emerge or removed by careful use of a hoe, but it is important to find compost or organic material which is not full of weed seeds. Harvesting from no-dig beds is easy because the soil is not compacted, so the plants can be pulled out without digging. In some cases (e.g. spent leguminous crops) the plants are cut off just below the soil surface and the roots left in the soil. The organic layer on the soil surface reduces run-off and erosion.

On a larger scale the vast arable plains of North America which produce crops of wheat, soya and maize are regularly ploughed. This releases huge flushes of carbon dioxide which can be detected in the earth’s atmosphere by satellites during the ploughing season. Monocultures like this require regular use of herbicides, pesticides and mineral fertilisers causing the soil to become seriously degraded, and incapable of producing food in future without drastic changes. Regenerative farming is a promising way forward. This approach imitates the natural plant communities that originally inhabited the land. As in no-dig, the aims are to minimise soil disturbance, keep the soil surface covered, maintain living roots within the soil and maximise the variety of plants grown but unlike no-dig, livestock grazing is part of the ecosystem. Animals are grazed in small areas for short periods with long resting-times in between, and the grazing areas rotated maintaining a healthy, species-rich, self-sustaining pasture. The trampling of the surface is beneficial, and dung fertilises the ground and encourages bird and invertebrate activity. Food produced this way is nutrient rich, and meat can be produced on pasture alone. The invention of a no-till drill which inserts seeds below the soil surface has dramatically reduced the need to plough. Growing a range of crops this way keeps the soil healthy, spreads the commercial risks faced by farmers, increases resilience and enhances biodiversity. It minimises the use of chemicals and machinery.

Whilst regenerative practices focusing on soil health are being used for producing crops, another completely different technique is being explored for non-crop gardening. Originally occurring on disturbed ground, abandoned buildings, old industrial or quarry sites, habitats using gravel, rubble, stone or sand as a growing medium are surprisingly rich ecologically, and support a huge and diverse range of organisms. Sometimes referred to as brownfield gardening, the growing medium is about as far from ‘moist, well-drained soil’ as you can get. Concrete, bricks, stone, building waste and porcelain sanitary ware can all be crushed and used, in addition to naturally occurring substrates like stone, sand or gravel. The key is small pieces, as opposed to the large lumps of rubbish hidden under a thin layer of soil and turf in new build houses. You won’t be able to grow a good crop of potatoes in this, but it will support a huge variety of plants. Establishment may be slower, but the plants are remarkably sturdy, resilient and drought tolerant with extravagant root systems, and do not need staking. They are watered only when they are planted. Beth Chatto’s dry garden was one of the earliest gardens to try this. Peter Korn, a Swedish gardener, has taken it a step further by planting in pure sand, up to 40 cm deep, or into a shallower sand layer above other material. He washes all traces of soil off a plant before it goes in. At the end of the growing season all traces of dying plant material are gathered up and removed from the site. Sand retains a surprising amount of moisture and supports mycorrhizal and fungal communities.

As with all gardening matters, there are plenty of contradictions. But plants want to grow, and can succeed in a huge range of different environments bringing with them a multitude of other creatures, diversity and beauty.