Happy are they who have a deep, humus-rich friable loam as the soil in their garden. What can be done by those with “difficult” soils – the clays, sands or peats that some have to contend with? The answer is “quite a lot”, and in the next few paragraphs, we will give you some useful pointers.
Clay soils (aka “heavy” soils) are wet and cold in winter, with a “chewing gum” consistency. In summer they set like concrete and crack. They are often acidic. Sandy soils (aka “light” soils) drain freely, so they are parched in summer. They lack natural minerals so plants, apart from a few sand specialists, cannot thrive in them. Peat soils are soggy in winter and become very dry in summer. Once dry, they are difficult to wet again. They are often associated with a high water table and are often quite acidic. They are rich in nitrogen, but not much else.
On the positive side, clay soils contain many natural minerals. Properly treated, their water retention and nutrient-holding capacities make them among the most fertile soils for landscaping and planting ideas. Sandy soils have the advantages of remaining workable in the winter and of warming quickly in the spring. Once their deficiencies have been corrected – and that is not difficult – they can be a good growing medium. Peat soils have few direct advantages, but with drainage and treatment to reduce their acidity they make a suitable home for selected plants.
All soils are a mixture of material that originates from rock and material that originates from living things. The composition of soil is changing all the time, but under natural conditions that happen at a very slow rate. The action of the weather on rock gradually, over a very long time, produces sand and silt. Both physical (freezing, cracking, splitting, abrading) and chemical (carbon dioxide, oxygen, and acidic action and reaction) processes are involved. Sand particles are relatively large; clay particles are about one million times smaller than sand particles. The organic material in soil comes from both animals and plants; some living, some decomposing.
As well as the inorganic and organic material described above, healthy soil also requires moisture and air. Without air, many of the bacteria involved in the decomposition of organic matter cannot live and work. Without moisture, nutrients in the soil cannot be taken up by plants. The balance of mineral particles, organic particles, living organisms, moisture and air that makes up a particular soil determines its qualities as a medium for plant growth.
To improve clay soils we need to attend to drainage, aeration, and excess acidity. Where clay soils are constantly saturated drainage may be by open drains, stone drainage pits, field tiles or plastic perforated drainage pipes (field tiles and plastic piping should be available from local landscaping contractors or companies). Where the soil is not totally saturated, alternatives can be used, such as raising the garden beds or breaking up the subsoil, especially if there is a hard pan, common in clay soils, that prevents water draining away. However, just draining the water will not do much to improve the structure of the soil. To do this we must add organic matter. The starting (and, some argue, the ending) point is the addition of plenty of organic material in the form of well-made compost. Over time, as this is incorporated into the soil, problems of aeration and moisture regulation will be solved. In the meantime, it can be useful to add lime to counter the clay’s acidity, and general fertilizers to support plant growth which, by the action of roots and decaying plant material, will also help to transform the soil.
Sandy soils are easier to correct than clay ones. The addition of organic matter – compost – will allow the sand particles to hold water and nutrients once they are coated with the humus you have introduced. Many nutrients will be contained in the compost, but not always in sufficient quantities to promote the required plant growth. So a thorough program of fertilizing the garden should also be adopted.
Peat soils are formed in swamps; so if you have a peaty area designated for your garden plans, you may like to find out something of the history of your area. Was the original swamp drained by human activity, or through a natural event? Is the water table still high, or has the water drained right away? A high water table can cause problems in winter, and can also create difficulties for growing trees. Solutions to a high water table can mimic some of those used for clay soils – drains and raised beds can both be helpful measures. Because peat is very acidic a robust program to apply sufficient quantities of lime will be required. Just how much is “sufficient” will depend on the pH of the soil. Some testing may be needed to establish this. Kits for testing pH are available from landscape suppliers and garden centers.
Understanding the composition of your soil is necessary for pictures perfect landscaping and gardens. A little knowledge opens the door to solutions that can make even “problem” soils productive.