I ran this trial at Lower Farm for six years, and have run a very similar one at Homeacres for another seven so far, including in 2019. The Lower Farm trial consisted of four smaller beds, each measuring 1.5 × 2.5m (5 × 8ft). When I moved to Homeacres, I simplified it to one bed of each, but with the same total area.

When I began the comparison in 2007, I had no idea whatsoever how growth would differ between dig and no dig, because I did not dig as part of annual soil preparation.

The harvest totals for Lower Farm (2007–12) were:

• 376 kg (829 lb) from the dig bed
• 400 kg (882 lb) from the no dig bed

(Follow the link at the  bottom of the page for more information on the Lower Farm trials.)

As well as higher yields from no dig, I observed other notable differences. The soil was much easier to weed and water on the no dig beds at Lower Farm, and I noticed that parsnips rooted more deeply! The results at Homeacres have been broadly similar. Soil at Lower Farm was clay, and at Homeacres is silt over clay.

Yields from the two Homeacres’ beds, in the seven years between 2013 and 2019, totalled:

• 656 kg (1446 lb) from the dig bed
• 728 kg (1605 lb) from the no dig bed

(See the graph below.)

Over the two sites, and in 11 years out of 13, the no dig bed was higher yielding.

Mostly there is not a huge difference between the beds, but a common variation is stronger growth in early spring in the no dig bed. In the cold spring of 2018 this was especially marked – seedlings started strongly in surface compost, compared to loosened soil into which the compost was incorporated while digging.

To a gardener who habitually digs, the dig bed’s soil would appear absolutely brilliant – soft and friable. Until you see the difference in growth. I suspect that, among other things, there is damage to fungal networks (see Lesson 14).

In spring 2018 there was more slug and wireworm damage on the dig bed, which contradicted the common assertion that ‘digging allows birds to eat pests’. What this statement should mention is how digging allows birds to eat worms, and other beneficial inhabitants of the soil. This disrupts the natural and fragile balance of pest and predator, for example ground beetles (Carabus violaceus) that eat slugs. Other beetle species climb plants to feed on aphids and caterpillars.

There is still plenty to be discovered about how soil organisms interact, and I reckon most of it will highlight the value of no dig/no till. My trial results point to that, as do the photos below.

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The growth differences revealed by this trial have now been consistent for 12 years, and lead me to question a lot of things, such as why the method of digging is so promoted and respected, even though it requires more time and results in inferior growth, less moisture retention, more weeds, more pests and worse drainage. Not to mention muddy boots and roots.

I suspect the answer is psychological, a desire to ‘fit in’ and be like other people. Also religious – the need for hard work, and to have dominion over nature.

Thankfully there are now enough ‘no diggers’ for these reasons to count for less. Have a look at the Facebook group ‘No Dig Gardening – Undug’, for example. It started in 2013 after a weekend course at Homeacres, where a few of us were lamenting the predominance in ‘no dig social media’ (such as it was) of permaculture using hay and straw mulches. The group keeps on growing – it now has, at the time of writing, 19,146 members, and two of the moderators were on that 2013 course: Stephanie Hafferty and Jan Wilmot.

This harvests of 19 June were:

These beds are a microcosm of the garden, with so many different vegetables in a relatively small area. They illustrate two important and often misunderstood aspects of vegetable growing:

1. Many vegetables grow in half a season and, after clearing them in early to mid-summer, there is time to grow another harvest for autumn, winter and spring. See the 2018 and 2019 results tables below for ideas of first and second plantings.
2. A four year rotation is not necessary, unless your soil has been abused over decades (or longer), by digging and careless growing. For example on some allotments there are soil diseases, such as clubroot of brassicas and white rot of onions. Most soils do not have these long-lasting problems and need less attention given to rotation – especially when the soil is healthy no dig.

This video is from October 2018;  we had already done a watering test of the same nature in August 2018. I was shocked by the difference, when imagining the effects of heavy rain on cultivated fields.

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Towards the end of summer, growth usually looks more even than in spring and early summer. Harvests are another matter however, for example the red beetroot and leeks we pulled in autumn, which looked similar when growing but weighed 15-50% more on no dig. The results of 2018 show a wider difference than I ever recorded, around 30% more harvests on no dig throughout the season. Perhaps it’s to do with a stronger response to the dry conditions, although we water both beds the same amount.

For the seventh time I dug the dig bed in December, and incorporated two large barrows of compost. On top of the no dig bed I simply spread the same amount, which settled to a layer of 2.5 cm (1 in). I also spread 25% of homemade compost and 25% of mushroom compost, not mixed together but each batch scattered evenly on top.

Spring growth of the dig bed’s potatoes was fine, but its spinach and beetroot were desperately slow, as in 2018.

A graph showing the weight of harvests from 2013 to 2019, and the gap widening.

I sent samples of soil from each bed, taken at a depth of 15 cm (6 in), to a microbiologist in Norway, Katelyn Solbakk.

The results of her study resulted in this paper, which included the table below.

Solbakk’s paper illustrates and explains the differences she saw in a microscope analysis of each bed’s soil, and can be summarised as follows:

‘There was a very noticeable difference in the physical condition between the dig and no dig samples. All samples did appear to be rich in organic matter, but the no dig samples were exceptionally clean and well aggregated. The structure was significantly weaker in the dug soil, with more loose, unbound debris and fewer large aggregates. The no dig samples had a very clean appearance with large, strong aggregates and very little unbound material.’

One hears little about protozoa, but here is what Katelyn has to say about them on her website:

‘Protozoa are important but often under-appreciated members of the soil food web. The main ecological role of soil protozoa, as it is currently understood from our perspective, is to free up nutrients that have been immobilized by bacteria, completing what is known as the “microbial loop”. Different species of protozoa are known to selectively hunt particular types of bacteria, so if there are many types of protozoa, it could be a sign that there are many types of bacteria as well. Protozoa have also been found to provide benefits to plants that extend beyond the release of nutrients, such as improved growth and disease resistance.’

Of the samples taken from each bed, Katelyn wrote:

‘In these samples, there was a considerable improvement in protozoa abundance and diversity in both the no dig trial bed and the full garden sample, compared to the dug bed.’

The dig beds need more time than no dig:

• Around two and a half hours for digging
• An extra half hour through the season for weeding

Disturbing soil causes weed seeds to germinate (see Lesson 9 and the photo comparison below).

The classic reason given for this is that cultivation exposes some weed seeds to the light, triggering their germination. I think another reason is that disturbed soil needs to heal,  and weeds are part of the healing process. We see an example of this with chickweed, which grows so fast after the passage of a rotavator –  I know this from experience!

The photo of surface conditions between the parsnips (in July 2010), is after four weeks with just 27 mm (1.1 in) of rain, and afternoon temperatures of 21–24 °C (70–75 °F). No water was given, and the dug clay is cracking along the lines where my spade had entered, allowing a lot of moisture to escape.

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Following my work to promote no dig, I am heartened to see its uptake by official bodies, who, until recently, were following well established but old fashioned Victorian methods. For example, the current gardens manager at RHS Wisley heard me lecture on no dig at Kew Gardens in 2011 and decided to give it a try on her allotment. The results were so consistently good that she has introduced the method to students at Wisley in Surrey, and to apprentices studying there. Wisley’s edibles garden is now no dig.

Kew Gardens in London give each of their students a bed, to grow vegetables and then be examined on. Since 2018, these beds have been no dig. Many National Trust gardens are now no dig too.

Another significant trial started in 2016, at Beechgrove garden in north east Scotland, near Aberdeen. The garden is run entirely for the BBC television series ‘The Beechgrove Garden’. They set up two areas side by side – one dig, and the other no dig – and initially were sceptical of how the no dig plants would grow. Each year the no dig vegetables have grown strongly, to the point when, in November 2018, they decided to convert all of their vegetable growing to no dig.

You are in good company!

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