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Lesson:

No Dig Gardening

Comparing dig and no dig for 13 years - what the differences reveal

Every year, since 2007, I have grown vegetables and recorded the harvests from dig and no dig beds, each with a surface area of 7.5 m²(81 ft²).

. Yields over 16 years, from 2007 to 2022, totalled:

1327 kg (2926 lb) from the dig beds
1471 kg (3243 lb) from the same area of no dig beds

These weights are of trimmed vegetables, and from the same plantings on both beds (at Lower Farm and then at Homeacres), with the same amount of compost added to each bed.

Compost is spread on top of the no dig bed.
Compost is incorporated into the dig bed, as in traditional gardening practice.

(See Lesson 5 for a trial where compost is on top for both.)

Two identical trial beds

I started this trial at Lower Farm in 2007 and ran it for six years. Since then I run a similar one at Homeacres for another 10 years so far, including 2022.

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 method, 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. I had used a tractor rotovator in the early 1980s, but never 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.)

Strong differences in results

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.

1. Charles digging in December 2012 when the Homeacres trial began — Charles digging in December 2012, when the Homeacres trial began

1a. Tipping compost (old cow manure) into the trench, after each one is dug out — Tipping compost (old cow manure) into the trench, after each one had been dug out

On the same day – filling the no dig bed with the same amount of compost that we had added to the dig bed’s trenches

1c. Two months later I laid cardboard on the weedy paths, and some wood shavings on top of the card — Two months later – I laid cardboard on the weedy paths, and some wood shavings on top of the card

Over the two sites, and in 14 years out of 16, the no dig bed has been 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.

In 2022, there was a huge growth difference from April to June, of peas and onions in particular. Every year there are standout differences, and not of the same vegetables.

Of all the vegetables I grow for comparison, potatoes give harvests which are the most similar between each bed. Other vegetables show more variations between dig and no dig, for whatever reason.

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

2. I am digging in December 2017, then dropping compost in each subsequent trench — December 2017 – after digging, I dropped compost in each subsequent trench

2a. Trial beds ready, dig left and no dig is compost mulched, Finn is stabilising the sides — The trial beds are ready – the dig bed is on the left; the no dig bed has been compost mulched, and Finn is stabilising the sides

3. We made the first plantings and sowings on 31st March, then covered beds with fleece. This is 15 days later. — We made the first plantings and sowings on 31 March, then covered the beds with fleece; this is 15 days later

4. Final removal of fleece on 3rd May, after mostly cold and dull weather in April. See some strong differences already, especially at the further end. — 3 May – the final removal of fleece, after mostly cold and dull weather in April; you can see some strong differences already, especially at the further end

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.

This 2022 YouTube video shows the growth differences in that spring plus summer, and over 10 years.

Growth differences – 2018

5. 21st May 2018 dig bed closest with (l to r) onions, kohlrabi, potatoes, cabbage, lettuce, carrots, beetroot, spinach, peas — 21 May – the no dig bed is closest, with (left to right) onions, kohlrabi, potatoes, cabbage, lettuce, carrots, beetroot, spinach, and peas

6. 21st May 2018 no dig bed closest with (l to r) view of cabbage, lettuce, carrots, beetroot, spinach and peas — 21 May – the same view, further to the right, with cabbage, lettuce, carrots, beetroot, spinach, and peas

27 May – end view, with the dig bed on the left and the no dig on the right; onions, kohlrabi, and potatoes are in the foreground

8. By early June there is a new planting of celeriac next to the peas, while spinach has only one more week of picking before it flowers — By early June there is a new planting of celeriac next to the peas, while the spinach has only one more week of picking before it flowers

Harvests of 19 June – from the dig bed on the left and the no dig on the right

10. I harvest Casablanca potatoes in late June, it’s a first/second early variety — Late June – harvesting Casablanca potatoes, a first/second early variety

11. 28th June and I have planted Cavolo Nero kale between carrots which are soon to finish — 28 June – I have planted Cavolo Nero kale between carrots, which are soon to finish

12. By 15th July the beds have mostly new plantings, only onions still to pick of the first plantings — 15 July – by now the beds have mostly new plantings; of the first plantings, only the onions are still left to pick

24 July – the dig bed in front and the no dig behind; these are second plantings after summer harvests – leeks, celeriac, celery, frizzy endive, kale, carrots, red beetroot, French beans, Golden beetroot, cucumber, and onions drying

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:

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.
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.
During 2022, I had feedback from two different allotment holders who were successfully growing brassicas in soils where clubroot had been prevalent three years earlier, when they took over the plots. Since then they have been no dig and results keep improving.

Watering test

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.

13a. 2x12l (12l = 2.7gal) cans half empty, watering between carrots on the dig bed — Watering between carrots on the dig bed, with 2 × 12 l (2.6 gal) half-empty cans

13b. after the cans had just finished watering the dig bed in about 30 seconds — The dig bed, just after 30 seconds of watering

13c. 2x12l (12l = 2.7gal) cans half empty, watering between carrots on the no dig bed — Watering between carrots on the no dig bed, with 2 × 12 l (2.6 gal) half-empty cans

The no dig bed, just after 30 seconds of watering

Harvests – 2018 example

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.

14. Aerial view 15th September, all second plantings made in the summer with dig bed on left, no dig on right — An aerial view from 15 September – all second plantings made in the summer (the dig bed on the left, no dig on the right)

15. 20th September harvests - carrot 0.41kg dig and 0.75kg no dig, plus beetroot 2.19kg dig and 3.15kg no dig; and the same number of roots from each bed — Harvests from 20 September – 0.41 kg (0.9 lb) of carrots from the dig bed and 0.75kg from the no dig bed; plus 2.19kg of beetroot from the dig bed and 3.15 kg from the no dig bed – each bed had the same number of roots

16. 9th October with dig bed on left, and lettuce are cropping where onions were, plus Kaibroc broccoli has followed cucumber — 9 October (dig bed on the left) – lettuce are cropping where onions had been, plus Kaibroc broccoli has followed cucumber

14 October – the final harvest of June-sown Nantes carrots, above 1.07 kg (2.4 lb) from the dig bed, and below 2.51 kg (5.5 lb) from the no dig bed, 132 days since sowing

A table of results from 2018 – first and second plantings

Harvests – 2019

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.

Frost on 6 May – there is fleece over the potatoes (the dig bed is on the left)

A table of results from 2019 – first plantings

A table of results from 2019 – second plantings

7 year’s results in graphic form, 2013-17 — A graph showing the weight of harvests from 2013 to 2019, and the gap widening.

Measuring the soil differences – October 2019

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.’

Katelyn’s microscope analysis of soil – from the dig bed (left), and the no dig bed (right) – shows the aggregation of the no dig soil creating better resistance to erosion, with less 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.’

A table from Katelyn Solbakk’s report, showing the evaluation of protozoa in each bed

Time and weed differences

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!

18. April: Surface example of the dig bed with spinach, beetroot, and weed seedlings growing — April – the surface of the dig bed, with spinach, beetroot, and weed seedlings growing

19. Surface of the no dig bed: same day, same crops and clean compost — The surface of the no dig bed on the same day, with the same crops and clean compost

19a. Dig bed Lower Farm 2010, soil for parsnips was dug in winter, compost dug in here in a dry July, it is cracking — The dig bed at Lower Farm in 2010 – the soil for parsnips was dug during winter, and compost was dug in; here, in a dry July, it is cracking

19b. No dig bed Lower Farm 2010, soil for parsnips was not dug in winter, here in a dry July, it is not cracking — The no dig bed Lower Farm in 2010 – the soil for parsnips was not dug during winter and, in the same dry July, it is not cracking

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.

Trials and uptake elsewhere

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.

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You are in good company!

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23. The RHS give each student or apprentice at Wisley, Surrey, a plot which is half no dig and half no dig — At Wisley, in Surrey, the RHS give each student (or apprentice) a plot which is half dig and half no dig

I am with Jim McColl at BBC Beechgrove’s garden in NE Scotland, where their trial of dig and no dig beds has recorded stronger harvests from no dig, from 2016-18 — Here I am with Jim McColl, at the BBC’s Beechgrove Garden in NE Scotland, where their trial of dig and no dig beds has recorded stronger harvests from no dig, from 2016–18; Jim was sceptical at first, but now loves no dig

No dig trials Homeacres — The other Homeacres trial (described in Lesson 5) – the nearest bed has cow manure compost, the other two have compost that is half mushroom and half green waste; the furthest bed has also been forked

From Seed to Harvest