My soil is a heavy clay. Although I have been adding home made compost to it for the last twenty years since we first made these deep beds the soil remains dense; cold in winter and like concrete in summer. Today I took a new approach as I prepared the bed that I have ear marked for runner beans.
First I dug a trench at one end of the meter square plot. I put all of the soil into a wheel barrow as I removed it. As I did this the soil was mixed with the layer of home made compost that I put on top of the bed earlier in the week.
Then I forked over the bottom of the trench. You can see the more yellow clay sub soil, I needed to be careful not to mix this with the top soil.Then I added a layer of compost material, this included kitchen waste and some half rotten material from the compost heap. Usually it is important to only add well rottend compost to the soil because of the ‘nitrogen robbery’ which occurs when micro organisms break down organic matter. However, because I am planning to plant beans which can fix their own nitrogen this is not an issue in this case. I forked this into the sub soil.
Next, I filled this trench by digging a new trench alonside the first one. I then repeated the process until I had got to the end of the plot and was able to fill the last trench with the top soil from the wheel barrow.
The finished bed was noticeably higher than the bed next to it. In the next few days I plan to top dress it with some more compost and cover it with a layer of cardboard. I have half a mind to plant runner beans as well on the adjacent plot (currently underneath the pallets) so that I can compare the effects of double digging compared to my usual approach of applying a layer of home made compost once or twice a year.
Here you can see the profile of the soil prior to double digging. The organic rich layer and the humus does not seem to be very deep at all before the clay is reached; this is clearly an aspect of the vegetable plot which needs a lot more effort!