The following article first appeared in ‘Grow your own’ magazine back in February as part of my ‘Theory Behind…’ series.
In traditional gardening and farming, land is weeded and/or cleared of crops before a soil improver such as compost and/or manure is dug or ploughed into the soil to improve the soil structure, aerate the soil and add nutrition.
With ‘no-dig’ or minimum tillage the soil is disturbed as little as possible. Instead a thick mulch, usually in the form of compost or manure (or sometimes leaf mould, straw or mushroom compost), is left on the surface of the soil for worms and other soil fauna to work in. The action of the soil life brings down the mulch, whilst naturally aerating the soil and improving its texture and fertility. The mulch is sometimes applied over a biodegradable weed barrier such as cardboard or wetted newspaper or the mulch is placed under a weed barrier such as mypex or black plastic sheeting.
Science of no dig
No dig gardening works on the principle that soil is a complex mix of living organisms rather than a dead substrate. In a single gram of soil there can be well over a 1000 million organisms, most of which live in the top few centimetres, this is often referred to as the soil biota. Worms and larger soil life work down organic matter into the soil creating air pockets as they move around. Then organisms in ever decreasing size break down this organic matter into its component parts which frees the up nutrients into a form our plants can take in.
As it concentrates on soil biota many consider no-dig gardening a way of feeding the soil rather the plants within the soil.
As most soil life exists in the top few inches of soil removing it to get rid of weeds can be detrimental to the fertility of the soil. Also with the removal of the topsoil, soil structure can be compromised and therefore more prone to erosion through wind and rain. In extreme circumstances this caused the great dust bowl in America in the 1930’s as ploughing took away much of the deep rooted grasses keeping the soil intact.
A key principle of no-dig is therefore to always keep the soil covered, be it with crops, compost, green manure or black plastic.
Mulching the soil will lead to less water loss through evaporation so no-dig plots are often use far less water than plots without soil cover.
The basics of no dig
Preparing a no-dig bed
Although not crucial some prefer to avoid walking on no-dig beds. For this reason beds should be set out to be no wider than the maximum reach the smallest person working the plot (preferably an adult!) can stretch to. On average this is a width of around 1.2m or 4 feet in width (or 60cm/2 feet from either side). Any wider and the bed becomes impossible to work without toppling over into it or deliberately stepping onto it. The beds can be as long as your land allows.
You can coat the ground with a double layer of cardboard (usually wetted), covering this with a layer of compost, a couple of inches deep, before sowing into it. Some will prefer to have the soil raised up in wooden bed but others claim this merely gives a habitat for slugs and will just sow straight into the compost. Also, some gardeners may prefer to clear the ground of perennial weeds first but others say this is a wasted effort as the cardboard blocks out the light preventing any weeds from growing.
You can cover a growing area in black plastic for a season to eliminate the weeds (again you may want to dig out any persistent perennials). Then peel back the plastic and cover with a layer of compost (2.5 cm to 6 cm or 1-2.5 inches). Either sow into the compost (with the plastic removed) or cut into the plastic and sow through it.
|Method 1||Method 2|
Interview with Charles Dowding
Can you very briefly explain how you use the no dig system on your farm in Somerset?
Every year, preferably but not always after last harvests in autumn, all beds (open sided, no wood) are spread with an inch or two of either cow or horse manure, home made compost or mushroom compost. All weeds are pulled when tiny so there are rarely many to be seen. Many beds are cropped twice each year with module grown plants from my greenhouse.
What are the draw backs with no-dig (if any)?
None really but it may take some getting used to, for instance sowing into compost rather than into soil. Starting off from a weedy patch takes time for mulching to be effective, up to a year for perennial weeds: an initial dig may seem quicker but a patient mulch results in cleaner soil.
Are there any crops that do better or worse?
Where I compare the same vegetables on dug and undug beds, harvests of spinach in May and beetroot in June are bigger on undug soil. Onions are bountiful and parsnips grow beautifully long into my clay, but potatoes make funny shapes unless some extra compost is used to “earth them up”, or you can pull surface soil around potato plants. Total harvests in dug and undug beds are broadly similar.
Criticisms of no-dig
Some studies have suggested that there may be a crash in soil fertility a number of years into a no-dig plot. However its advocates, including Bob Flowerdew, hotly dispute this claiming to have used the method for a number of years without the crash.
Others simply like the exercise of digging and feel no-dig robs them of this pleasure.
However, perhaps the biggest drawback to no-dig gardening may be the need to import organic matter. Charles Dowding disputes this and claims he only uses extra compost to supress weeds and lift fertility. He argues he only does this to remain commercially competitive and home growers may not need such high amounts of compost.
If this importing were necessary it is hardly as strain as local stables, city and rural farms along with community compost schemes will readily supply organic matter to growers, often either for free or for a small donation.
Grow your food for free …well almost - Dave Hamilton, Tips on how to construct raised beds and make compost heaps (amongst other things)
Vegetable Growing Course Book, Charles Dowding”, Frances Lincoln, March 2012 Organic Gardening The natural no-dig way, Charles Dowding, Green Books 2007
The One-Straw Revolution, by Masanobu Fukuoka, Rodale Press in 1978.
Gardening with Compost F.C. King, Plum Tree Publishing Ltd, Revised edition Dec 2002