I’ve had this book for a long time.
It was one of a number of books that I picked up
when I started to get really serious about growing my own food.
Out of all the books, this one made the boldest promise,
to be able to produce huge amounts of food from very little land.
There is a lot in this book, but at its core is a simple idea.
By deeply digging the soil in fixed beds and incorporating large amounts of compost,
a huge yield can be produced from very closely spaced plants.
For this reason I am using the Intensive methodology
to manage one of the six family size gardens in the RED Garden Project.
The Intensive approach had been adopted by many growers over the years,
but a lot of the techniques have been refined and changed.
Many have shifted to the use of a broad fork for an easier and less invasive deep cultivation of the soil.
Others are growing intensively using minimum tillage or have shifted to a no-dig approach.
For a number of reasons, I have stuck with a the use of double digging to prepare the
fixed beds of my Intensive Garden each year.
I wanted to see what would happen if I used this method for a number of seasons, and it's
an appropriate technique for the scale of a 100m2 garden.
There are also specific conditions on the site of the garden where I feel that a
Double Digging approach has been of significant benefit, so far.
But first, what is double digging?
At its simplest, it involves digging a trench across the width of the fixed bed and then
loosening up the soil at the bottom of this trench.
The trench is then filled with the soil from the next section of the bed,
creating a new trench and the process is repeated.
Done reasonably carefully, the basic stratification of the soil is maintained, and there is no
aggressive tilling to cause significantly damage to the earthworms and other soil biology.
Compost is usually added to the surface of the bed, either before or after digging, and
more can be added to each bottom of each trench as well.
By repeating this double digging and the addition of lots of compost for a number of seasons
the aim is to end up with loose, friable and enriched soil,
twice as deep as what would be possible with normal cultivation.
All of this enables the plant roots to more easily colonise a greater volume of highly
fertile soil, leading to much faster and more abundant growth.
That's the theory anyways.
In reality, the work to establish the 16 beds of my Intensive Garden
was spread out over a number of years.
This was due primarily to the presence of a lot of rocks in the soil, and not having
enough time for the first few years to adequately deal with them.
Although the top 20-25cm of soil was reasonably clear of stones, below that was a layer of
fairly densely packed rocks, which often required a pry bar to work them loose.
But interestingly it is only a relatively thin layer
and the subsoil below often contained fewer rocks.
This rock layer seems to extend across the whole site and is a key context issue for
the 6 different gardens.
This rock layer obviously posed a challenge to the double digging method, but there was
an incentive to remove them, if I was willing to put in the work.
And it was a lot of work, with several wheel barrow loads of rocks of various sizes being
pulled out of each of the beds.
But now that the task is done, there’s only a few smaller stones to be found and the job
of double digging is relatively easy.
The top layer of soil is easy to move with a spade, and the bottom layer of soil is easy
to loosen up with a fork, and the roots of the plants now have ready access to the subsoil below.
It's hard to determine how beneficial this structural transformation within the root
zone will be to the growth of plants.
No doubt if this rock layer hadn't been removed the plants that wanted to send their roots
deeper would have eventually found their way through the spaces between the rocks.
But carrots and parsnip definitely love the deeper loose soil.
I can also shift to an easier and less invasive use of a broad fork to loosen the soil most
seasons, something that would have been impossible before this rock layer was removed.
For the first few years of cultivating this garden I didn’t have access to much compost,
but for the last few seasons I've been able to add 2 wheelbarrow loads of compost to most of the beds.
One wheelbarrow load was spread over the surface before digging, which ended up getting mixed
into the top layer of the bed.
An additional wheelbarrow load was used to amend the lower layer, adding a bit of compost
to the bottom of each trench before forking it in.
Spread evenly over the 4.25m2 of a bed, this amount of compost would have produced a layer
almost 5 centimetres thick.
This is all worked into the top 50cm of the soil, which translates roughly into 10% compost by volume.
For each of the past few seasons I have used almost 30 wheelbarrow loads of compost to
amend the 16 beds.
That is almost 3 cubic meters of compost for a 100m2 garden each year.
That is a lot of fertility, but thankfully I had an abundant supply from the
No-Rules Community Compost and I also wanted to see what would happen if I really boosted the
organic matter in this sandy loam soil.
This season I am moving away from the soil building approach and using more of a sustaining strategy.
Instead of mixing the compost into the full depth of the bed, I am adding compost to the
surface after digging, and only mixing it in to the top 5-10cm of soil.
This approach is more in line with natural systems where organic matter is added to the
surface, and will eventually re-create a more natural stratification within the soil.
In addition, I am only adding 1 wheelbarrow of compost to most of the beds, which will
produce a layer of about 2.5cm thick.
But what is the result of all this work and fertility?
Is the extra effort worth it?
Looking at one example, last year's parsnip crop in this garden produced a yield of about
20kg from one square meter of bed, with each root averaging about half a kilogram.
In comparison the adjacent Extensive Garden produced only about a quarter of the yield,
with roots only half the size on average, even though they were given twice the space to grow in.
In addition, the roots from the Intensive garden were substantially longer and less
forked, thanks to all the rocks being removed.
Of course the results of one exceptional crop in one season is not enough to prove anything,
but I have had similar results from the previous year.
Perhaps I have yet to figured out how to get the most out of the Extensive Garden.
I don't have enough data to do a proper comparison across the other gardens, but the trend across
a number of crops seems to be similar.
This intensive approach seems to be living up to bold promises.
I still have a number of questions about all of this.
Does the double digging, the close spacing and the extra fertility equally contribute
to the higher yields, or is one aspect far more important than others?
How much more can the yield increase?
How does the nutritional density of the crops from the Intensive Garden compare with the other gardens?
Now that the beds are established would it be better to shift to a no-dig method,
to enable the development of a more natural, less disturbed soil biology?
I don’t have answers to any of these questions, yet.
For the last few seasons I've had enough compost, enough time and didn't mind the hard work,
which ends up being about 10 hours of double digging for all 16 beds.
I believe that the additional work that I put into removing all of rocks will be of
significant benefit for many years to come, and the increased fertility is definitely an asset.
Although, I will need to do a soil test to determine how the balance of nutrients can be improved.
But, according to the law of diminishing returns, additional fertility and looser soils will
at some point no longer translate into improved yields.
The cool growing conditions, the windy site and lack of sun that is typical of this climate
will place limits on possible growth, or some other factor will.
But I don’t know if I’ve reached that point yet, or if significantly better yields are possible.
And I won’t know if I don’t continue with this experiment.
I have been working on these 6 gardens for a number of years now, but it’s only recently
that I've been able to devote enough time, and to maintain a consistent attention throughout
the whole season.
As a result I'm only starting to gather meaningful data that can be used to compare the different
gardens, but I'm really looking forward to seeing what happens in the coming seasons.
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