Soil preparation is a term which covers all aspects of getting the soil in your garden ready for your plants. It includes checking the pH of the soil, and the nutrient levels; finding out what type of soil you have – clay soil or sandy soil for example; the digging of the soil itself; and adding soil improver, compost or organic matter to your garden soil.
Whilst digging is generally thought of a task for the winter garden, there are times when you need to dig at other times of the year; perhaps because you’ve asked us to create a planting design for you to plant yourself; or maybe because you’ve taken on an allotment.
What is double digging?
Double digging is a method of deep soil preparation in which the soil is loosened to a depth of 60 cm (2 feet) or two times the length of a spade’s blade and fertilized, improved, with organic matter.
Depending on what state your garden borders are in, the soil preparation can take quite a bit of time and energy. It is worth the time and effort (or getting someone else to do it if you’re not able to). Soil is the food that will keep your plants happy and healthy.
Double digging is labour intensive, but is a less exhausting method of soil preparation than triple digging, where the soil is excavated to three times the spade depth. The Victorians were great ones for cultivating the soil and used to refer to double digging as ‘bastard trenching’ being an inferior method of introducing organic material to improve the soil when compared to triple digging.
Dig or No-dig?
There is of course, the whole dig / no-dig argument, but for most people when faced with borders in their garden or an allotment, they will want to make use of what soil is there already and improve it. No-dig gardening is well suited to cultivating flowers, vegetables and fruit in raised beds, but we will look at no-dig in other situations in a later blog. Or you could take our gardening lessons to find out how to use this cultivation method in your own garden.
In fact, learning about soil preparation and how to dig properly with the correct tools for you and your garden is an early part of the Practical Gardening for Beginners course.
Where the borders or allotment have been cultivated and organic matter added on a regular basis, even if not for a couple of years, single digging is usually sufficient. The principle of digging out a trench and adding compost is fundamentally the same for both single digging and double digging.
Soil preparation where double digging is required or advisable
- cultivating soil in new gardens, where the builders may not have left you much top soil
- where you have a heavy, unworkable clay soil
- where you need to improve the nutrients of a soil by incorporating organic matter at root level rather than as a mulch
- creating new borders; perhaps in an area that has been lawn
- if you’re planning an orchard or even a few fruit trees planted together in one area; a good deep layer of top soil is useful
- where you have invasive, perennial weeds such as bindweed or ground elder; although there are likely to be some weeds remaining, it’s a more thorough weeding practice than just digging them up individually.
- on an allotment, where it hasn’t been cultivated for a while
- regenerating a perennial or mixed herbaceous flower border
Advantages of soil preparation using double digging
It will: –
- increase the amount of space in the soil for air and water, which in turn improves plants growth.
- improve the soil structure, especially when compost or manure are added.
- promote earthworms and the activities of soil microbes.
- break up soil crusts and hard pans, and increases the speed that water that can seep into the soil.
- help the soil retain water and nutrients when used with organic fertilizer
These advantages are the same for single digging if organic matter / compost is added.
Method for Soil Preparation by double digging and adding organic matter
NB: Do not mix the topsoil and subsoil.
The difference should be fairly obvious – top soil is generally darker in colour than sub soil as it has more nutrients.
Tools needed
- hoe
- digging fork
- rake
- digging spade
- wheelbarrow/s and trug
- tarpaulin or similar to put soil onto
Method
- Hoe off any annual weeds; if any perennial weeds will lift out easily with the hoe then remove those too
- Dig a narrow trench, across the width of the bed, about 30 cm (1 foot) wide, and about 1 spit/ 1 spade blade / 10” deep (you may or may not be able to see the subsoil)
- Remove any perennial weeds as you dig
- Set aside the topsoil you have dug out, either onto the tarpaulin or in the wheelbarrow; you will need it later.
- Using the digging fork, loosen the soil/subsoil along the bottom of your first trench to a depth of another 10-12”, ie the length of the fork tines/ prongs
- Now add some compost to cover the base forking/ mixing it in lightly.
- Dig another trench next to the first, in-filling the first trench with this soil; mixing in some more compost as you go.
- Continue this process until you have finished/ reach to the end of your border. You will notice that the level of the topsoil has been raised up from all the organic material being incorporated, as well as through breaking up the subsoil.
- You will have an empty trench at the end of the bed. Add compost as above, then bring the topsoil you set aside and put it into this trench.
- Lightly rake over the border when done, to level the soil.
Weeds seeds will probably germinate within a few days, hoe these off. Repeat as necessary until ready for planting. If any perennial weeds appear, dig out.
Two weeks is the usual time to leave a newly prepared bed before planting. This gives time for the weeds to be dealt with as above, for the worms and micro-organisms to start working their magic and for the soil level to settle.
When would you double dig a border?
Where we are creating raised beds as part of a garden design, we wouldn’t double dig, as new fertile top soil will be brought in to fill the raised beds.
However, where we are keeping existing borders or creating new flower and vegetable areas, we would double dig, adding plenty of soil improver.
The Victorians, and many ‘traditional’ gardeners (my Grandfather among them) like to re-generate even mixed herbaceous flower borders and shrub borders about every five years. This would include at least some double digging.
I have to say, although it is hard work, there is something distinctly satisfying about soil preparation by double digging. There is a visible result in all that turned over soil that can be quite beautiful when caught by the late afternoon sun.
Not that I dig everywhere; I’m also very fond of no-dig gardening in its various forms!
Related Gardening articles you may enjoy from our Award Winning Blog
Allotments and Allotment Gardens
Soil – the plant food in your garden
Your Garden in Winter: digging
Composting – a load of rubbish?
