Double digging may be hard work but it is perfect for creating new borders and deepening shallow topsoil.
Double digging is a useful way of cultivating soil in new gardens and in situations where deep topsoil is required. Ordinary digging is good enough for most circumstances.
Choose double digging over other methods of soil cultivation where the soil is compacted, where ground has not been previously cultivated, where demanding long-term plants such as asparagus are planned or when making raised beds. All bare ground is suitable for double digging.
It is not necessary to double dig every year, but on poor or heavy soils and in vegetable gardens it may be needed every three to five years. Otherwise borders only need double digging at their creation and on total replanting.
When to double dig
Double digging is ideally done in autumn and winter when the ground is moist, but not waterlogged or frozen. The ground then has time to settle after digging and, on heavy soils, for the frost to break down the clods before planting in spring. If the soil conditions are good, then double digging can be carried out any time of year.
How to double dig
What does double digging entail? Here are some steps to take;
- Use a line to mark out the area you are going to dig. Although you can buy lines, it's easy to make one with a cane pushed in at both ends of the plot and a piece of string stretched between them. Marking out the plot keeps the trench straight, making it less likely that the process will move too much soil to one end or the other
- Once the width is marked out, then measure approximately 60cm (2ft) back. Use a spade to dig out this area and temporarily place it to one side. Here the soil has been put on the right, but it could also be placed at the end of the row. At the end of digging the area, this soil is used to fill in the last trench
- Continue to dig the first trench, put the soil aside. The depth only needs to be the same as the spade blade
- Fork over the bottom of the trench. This is where the name 'double digging' comes from, as you dig twice the depth of usual, single digging
- Add organic matter, such as garden compost or well-rotted manure, to the base and lightly fork in
- Now measure approximately up the line another 60cm (2ft), and use a cane or stake to mark where to dig to
- Dig out the soil and place on top of the first trench (where the organic matter was incorporated)
- Once the soil is moved forward, you are now ready to repeat the process from step four to seven
- As you work up the plot, be careful to keep the top surface level. This ensures that the soil isn't shifted to one end
- Once you have reached the end of the plot, use a barrow to move the soil dug out at the beginning
- Pour it in the final trench to fill in the final top layer
Allow the soil to settle before planting. If dug in autumn, this usually happens naturally by spring. But if the soil is still very soft, lightly tread the plot first.
Double digging is not always necessary and if time and physical strength prevent this very hard work, be aware that ordinary soil cultivation is often good enough, or else you can make raised beds or control weeds with weedkillers.