When to double dig?
This is ideally done in autumn and winter when the ground is not frozen or waterlogged. This means there is time for the ground to settle before planting in spring. If your soil is good then double digging may be carried out at any time of the year.
Double digging is a traditional, Victorian method which involves the bed to be dug in sections in order to fork additional organic matter into the lower layer. Once forked, a layer of organic matter is lightly worked into the ground and topped with the next section of soil. This is then repeated across the beds.
- Mark out the area you want to double dig. Use canes with string tied on them to keep your line straight.
- Work in 1m square ‘blocks’ – using a spade dig the first square out, down to approx. 30cm deep, and place the removed soil onto the adjacent space.
- At the bottom mix in organic matter such as well rotted manure or garden compost and lightly fork in.
- Keep the top surface soil level across the plot, and back fill if needed.
- Repeat the process across the total space of the beds and once you reach the end of the plot, use the excess soil to back fill the initial ‘plot’.
Heligan uses the double digging method in the kitchen garden within the productive gardens. Of the 200+ acre estate, only one and a half acres use this method. This approach was born out of representation of a working country house from late 1900 productive garden and its rotations. The method creates a friable soil that’s easy to work with and sow into and it also replicates how these parts of the garden would have been worked in the Victorian times.
However, more recently the reason that we have continued to use this method in this area of the gardens is less about preserving a heritage horticultural practice, and more about creating a ‘control’ as part of a wider research study.
The University of Plymouth is conducting a research project into carbon sequestration, and also how different soil treatments can affect the nutritional quality of the vegetables grown in different kinds of soil – in our case, rainbow chard grown in soil which is uses double digging.
Because this particular part of the Kitchen Garden has been managed in a specific way for the last 30 years we are able to provide a ‘control’ set for data on key metrics of soil health, such as carbon sequestration and nutritional performance to our research partners, and therefore they (and we) keen not to change what we do, so we can continue to provide consistent data.
However, that’s not to say that one size fits all! There are other areas of the productive gardens, in particular the flower garden, where we are trialling a no dig approach. It is really helpful to compare the results of this experiment with the ‘control’ benchmark of the double digging Kitchen Garden.
We have also recently changed our approach to grazing across our pasture land, and with the support of Tim Williams, are now following a regenerative grazing method.
Across horticulture and scientific research there have been huge changes in the accepted approach for cultivating soil over the last few years. We now have a far more nuanced understanding of the biological functions going on in soil – it’s not just there to hold plants up – it’s a living, breathing ecosystem.
Soil is important everywhere at Heligan but different demands and needs across estate and gardens mean that we will continue to use the different and varied methods of management which best suit that area. In the Kitchen Garden in the Productive Gardens we’re continuing with double digging for the foreseeable because it provides an important ‘control’ benchmark data set for the University of Plymouth carbon research project.
We are awaiting confirmation of the start of the project but will keep our visitors and followers updated in due course.