The solution is really quite obvious: We have to dig our soils as deeply as possible and incorporate as much organic material as we can obtain. But this is only part of the overall strategy. We do not have several years where we can put our gardening aspirations on hold until the soil develops totally naturally, we have to give the process a little active encouragement.

Perhaps the best way to understand what is needed, is to consider how the soil on working allotments developed into such a wonderful growing medium: -

Clearly the process started with the allotment holder digging his soil in Autumn, probably bastard trenching (digging 2 spade depths), and adding either lime or manure to the bottom of the trench, bringing the solid clods of underlying soil to the top to be broken down by the weather, where the freezing and thawing process during Winter soon has the desired action upon clods of soil at the surface, breaking them down into finer particles. Over time the process would be repeated many times and eventually the soil would all be broken down into fine granules that bacteria could colonise.

The plot would probably have been divided into quarters, such that brassicas, would be grown in one quarter, potatoes in another, peas and beans in a third, and the fourth left fallow. Each section would have been treated differently, with heavy liming of the section where the brassicas were to be grown, and manuring of the other sections.

Remember that when our allotment holder first started to work his patch, the soil would most probably have been fairly sterile, and it has only been with time that the necessary soil life colonised this new haven.

It is said that growing potatoes improves the quality of one's soil, however, we feel that this is very much an old wives tale, and it is the additional digging required to lift potatoes that is really significant. The more the soil is turned over the better it becomes.

Our job is to try and condense many years of allotment style working of the garden soil into a few brief months, whilst being very aware of some of the problems that can arise: -

• If working with a clay soil, unless it is intended that your garden will be home to acid-loving ~ lime-hating plants, we will have to use serious quantities of lime, where through a process known as flocculation, lime causes the fine particles of clay to glue themselves together and form larger particles that behave totally differently to fine clay particles. This in itself helps to make the soil permeable to both water and air. The downside is that the soil may temporarily become excessively alkaline, until the action of manure and other organic material has its effect.
  
  

• I always use builder's lime for the purpose, it tends to be far more aggressive and speeds up the process of flocculation. Here one should use gloves, a mask and eye protection.
  
  

• Whilst digging your soil try to rescue any worms you come across, for they will be killed by the lime. Rescuing your worms is not a selfless act of wildlife preservation, you really will need as many worms as you can obtain in the near future, they are the real workforce in our gardens and will turn over more soil in a season than any gardener.
  
  

• Never mix sand, clay and builder's lime together at the same time unless you wish to create the equivalent of concrete.
  
  

• I always aim to dig down at least three feet, and start to incorporate large quantities of manure/compost at this depth. If the soil becomes compacted and airless then anaerobic bacteria can colonise any green material in the manure/compost, and rather than producing lovely sweet garden soil, they will produce foul smelling acidic slime. To counter this I always lay in bundles of branches to provide for the free passage of water and air, and sprinkle generous amounts of lime on the soil as the layers of soil and compost build.   

Most good gardening books advise that subsoil is never brought to the surface or the topsoil buried. Improving the depth of good soil in a garden requires that the subsoil is most definitely brought to the surface. There is no other way to start the conversion of subsoil into loam. It firstly has to be broken down into small particles that the helpful bacteria in our gardens can colonise, and then mixed with sufficient organic material to feed the process.

How you proceed depends upon your existing soil type, and whether you are aiming for an acidic, lime-free soil or a neutral to alkaline soil. If you live in a limestone or chalky subsoil region or are aiming to produce an acidic or lime-free soil the following steps can be followed, but excluding the use of lime. Unfortunately in the case of a solid clay subsoil, it is lime that helps to speed the process along through flocculation (essentially where the lime glues extremely fine clay particles together to make larger irregularly shaped granules), so if you are endeavouring to improve clay soil but retain acidity it will require more digging than otherwise might be necessary. 

How deep you dig to improve your soil is a matter of personal choice. However, the deeper you feel able to prepare your soil, the better. Here we have to keep in mind the fact that the climate in the UK is changing, and that during the Summer drought conditions and watering restrictions are beginning to make it difficult for plants to thrive in shallow soils. We would suggest that 24in (60cm) should be considered a minimum depth, and deeper, 3ft (1m), a real bonus. The easier we make it for the roots of our plants to penetrate deep into the ground to find the moisture and nutrients they need for growth the better they will thrive. 

Early Autumn is perhaps the best time to start any soil improvement campaign. The soil will be dry enough for clods of subsoil to break up reasonably easily once brought to the surface and abused a little, and the weather should be pleasant enough for the task of digging to be bearable. 

Having finished the hard work, your flower border will appear very light in colour. Indeed if you have brought enough subsoil to the surface and added sufficient lime, it will look nothing like the beautiful dark fertile soil that you are hoping for.

The next stage is to wait for the Winter wet and frosts to work their magic. The rain will wash the lime through the soil encouraging and accelerating the chemical reactions that will bind fine clay particles, and the frosts will freeze the clods of soil at the surface breaking them down into smaller pieces. The height of the soil in the new flower bed will be visibly reducing, and the colour of the soil will gradually be darkening. A close examination of the soil will probably reveal that the surface is being covered by a film of algae.