Double Digging
Double (or trench) digging is generally only used for soils with poor drainage or when the ground has not been previously cultivated. The trenches are twice as wide as those used in single digging (60 cm or 2 ft) and the soil is cultivated to 2 spits depth. As in single digging, weeds are removed during the process.
Medium and heavy soils should be dug during autumn or early winter to ensure that they are not too wet or dry to be worked. Sandy soils may be dug in winter or early spring, although you should ensure that the ground is not waterlogged or frozen.
Soil improvers such as lime, fertilizers and organic matter may be incorporated into the base of each trench. If you are working in a previously uncultivated plot, any turf may be removed from the surface and chopped up into the base of the trench.
Never dig heavy soil when it is frozen or waterlogged as this will permanently damage its structure.
Deep Double Digging
The deep double digging technique involves digging a trench 2 spits deep and moving all the soil from that trench into the trench in front. However, this method should only be used if your topsoil is more that 2 spits deep as subsoil should NEVER be mixed with topsoil.
Standard Double Digging
If your topsoil is less than 2 spits deep, you will need to use the standard double digging technique described below, as this will ensure that the topsoil and subsoil are kept separate and distinct. In this method, the lower spit is not brought to the surface - it is simply forked or dug over in situ.
- Mark out the area to be dug using canes and string. Mark off the first trench line at a width of 60 cm (2 ft).
- Dig the first trench to a depth of 1 spit (1 spade), collecting the soil in a wheelbarrow, or simply place it to one side.
- Fork over the bottom of the trench to the depth of the fork tines. Incorporate any soil improvers, such as lime, organic matter or fertilizers, into the bottom of the trench. Remove any weeds - especially deep-rooting perennials.
- Move the canes and string to mark off the next 60 cm (2 ft) trench.
- Dig the second trench to 1 spit depth, placing the soil from this trench into the first. Make sure that the soil has been turned so that any remaining annual weeds and weed seeds have been buried.
- Fork the bottom of the new trench and continue to the next trench. Work your way across the plot until you reach the opposite end. Make sure that you keep the top surface of the soil level.
- Use the soil from the first trench to fill the final trench.
- Do not walk in the soil once it has been cultivated and allow it to settle before planting. If you dig the plot in autumn, it should be ready to use by the following spring.
Double digging is good for poorly drained soils and deep-rooting crops.