One spit digging:
A spit deep is the depth of dig equal to the depth of the spade blade or fork tines.
Begin digging by excavating a trench approximately 1ft (300mm) wide and one spit deep, across one end of the bed to be dug.(pic 1)
Place the excavated material in a wheelbarrow or bucket, and cart it to the opposite end of the area being dug.
This will be used to fill the last trench.
When digging successive beds, do not take too large a bite of soil,
Your own strength, ability and soil type will probably determine what size of bite to take.
As a guide; push/jab the spade 3”- 4” (75-100mm) into the soil at right angles to the open face about a spades width from the edge or previous bite to determine the width of cut.
In practice you will probably find that this task can be executed with a quick jab of the spade into the soil.
Next, place the spade 6”-8” (150-200mm) back from the face of the cut and push it with the aid of your foot until it has sunk a full spade length (spit) into the soil.
Ease the spade back towards you to loosen the soil and lift it out and throw the soil forward into the previous cut.
Continue in this manner until the bed is completely dug.
Finally fill the last cut with the soil you transported from the first cut.
If your soil is quite heavy or lumpy,leave it as it is and let the winter weather work on it.
Periods of freezing and thawing during the winter months tends to break up the larger lumps into a more manageble tilth.
If digging is being done in spring, break the lumps down as finely as possible, and pick out any weeds as work progresses.
Sometimes when the soil is heavy or moist it sticks to the digging tool making it quite heavy to handle,to alleviate this, keep a stick or preformed scraper handy to clean the digging tool as necessary.
If manure is being added at this time, place this in each of the trenches formed during the digging (pic 2) and cover it with the soil excavated in successive rows.(pic 3)
The ideal time for manuring is early winter for heavy soil and late winter for light soil.
Generally on a plot single digging (1 spit deep) is sufficient, but sometime there is a need to improve the quality of poor, shallow, or badly drained soil and this is where double digging or bastard digging as it is sometimes known, can sometimes help.
This is not a task to be embarked upon lightly, as it will entail a considerable time and effort.
What is it ? and how often should it be done?
Basically it is 1 spit digging done twice as the names suggests.
Put another way, single digging is done in two layers where the top layer is dug with a spade, and the bottom layer with a fork.
Ground that has never been dug deeper than one spit deep, results in the sub soil below, becoming hard packed.
Plant roots find it difficult to penetrate the soil in this condition, hence the need to dig two spits deep (double dig).
Subject to soil improvements the task may require repeating every three to five years and in other cases never.
Rather than double digging the whole plot at once, consider doing one third of the plot in three successive years, and continuing to single dig the remaining two thirds of the plot until the task is complete.
This will result in the whole plot being broken up to the depth of approximately 2 ft (600mm) within three years.
The best time to do it is at the end of the season, and before the onset of winter.
This should ensure that the ground is workable and is not water logged or frozen.
It will also allow the excavated area time to settle, and in the case of heavy soil, time for winter frosts to break up clods .
Having said that, if the area is not in use the work can be carried out at any time.
Dig a trench 2 ft (600mm) wide and 1ft (300mm) deep across the bed.
Transport topsoil to opposite end of bed for use on the last trench.
With a fork loosen up the subsoil a spit deep.
At this stage fork in organic material into the loosened subsoil.
Section through Trench
Commence trench two.
Throw topsoil into first trench.
Loosen subsoil and add organic matter.
Repeat this process in successive trenches to the end of the bed, then fill the last trench with the topsoil from the first trench.
During this process always ensure that the less fertile subsoil does not mix with the topsoil.
Adding gravel / grit to the loosened subsoil will improve drainage.
Triple or deep trenching:
To improve drainage further you could triple dig i.e. three spits deep!
Start with a 3ft (900mm) wide trench 1 spit deep, remove and stack topsoil.
Excavate 2ft (600) wide trench 1 spit deep in subsoil and stack subsoil.
Excavate 1ft (300mm) wide trench 1 spit deep in subsoil and dispose of subsoil.
Section through Trench
Fill the deepest trench with rubble and stones to act as land drain.
Cover rubble with subsoil and organic matter to form second layer.
Then finally cover the subsoil with topsoil to form the top layer.
Proceed in this manner to the end of the bed.
Depending upon the contours of your plot you may be able to just do one strip using this method across the whole plot and improve the entire drainage on your plot.
Note, these techniques are not practical when the topsoil is only about one spade depth deep and is sitting on bedrock.
Faced with this situation the easiest way to increase topsoil depth is by forming raised beds!