1 Add soil to the surface to increase the depth.

2 Double-dig the whole area. To do this, open up a 60 cm wide trench at one end of the area and remove the top soil down to the clay base. Barrow this soil to the other end of the area where digging will finish. Break up the clay base with a pick or mattock but do not bring it to the surface.

Next, roughly work in amongst the loosened clay whatever manures, compost, etc, are available. Garden refuse, including annual weeds, can also be used. Then form another trench and turn forward the topsoil to fill in the first trench. Proceed in this way until the end of the area is reached. The soil removed from the first trench is then used to fill the last one.