Do you know what is in the soil of your garden and how it was formed? How it behaves in wet or dry conditions? Soil is composed of a variety of materials, some of which come from the actions of weather on rock, some from living sources, plus water and air. The base of soil is the rock near the surface. The material that comes from rock includes stones, sand, silt and clay. Stones and sand are fairly obvious and easily understood components; silt and clay less so. Silt is made of very fine particles and compares in texture to the finest powder.
Clay is composed of very fine particles too, even finer than silt, and it is the result of the chemical decay of rocks as much as their physical breakdown. Clay is chemically active, which means that it can bind strongly to itself, and other soil constituents. It bonds sand and silt together into tiny soil particles. The presence of a lot of clay causes too much binding so the soil can become a heavy, lumpy mass.
When plants and animals die, the remains are food for bacteria, fungi and algae in the soil. These, in turn, die and become food for other tiny organisms. The cycle continues until the original dead plant tissue is broken down into tough, insoluble materials such as waxes, resins and gums. Mixed closely together, these organic materials, dark-brown in colour, are collectively called humus.
Humus, like clay, is chemically active and bonds to other soil constituents almost like an adhesive. Apart from stones, sand, silt, clay, dead plant and animal material, living organisms and humus, soil also contains air and water, and plant nutrients released by the decay of rock material and organic material. A good loam soil is about 40pc sand, silt and clay, up to 10pc organic material, about 50pc divided between air and water, the balance depending on rainfall.
Soil is alive with living organisms, which are important to its proper functioning, but a tiny percentage, even under 1pc.
Soil types are described according to their main constituents so, for example, one with a lot of sand is known as sandy soil. However, soil with a lot of organic material is generally called peaty soil because it tends to contain peat. If soil has a good balance of sand, silt, clay and organic material, but no preponderance of any, it is called a ‘loam’. It might tend a little towards sand or clay and this would define it as a ‘sandy loam’ or ‘clay loam’. Sandy soil feels gritty between forefinger and thumb, silt is smooth and clay is sticky and greasy.
There are peaty soils and other poor soils associated with them in parts of many counties in the Midlands, west and north, particularly in mountainous areas, but most Irish lowland soils are loams.
There are well-drained, sandy or shaley loams in part of Kerry, east Cork, Waterford, Kilkenny, Carlow, Wexford, Wicklow, Dublin, Louth, Armagh, Down, Derry and Antrim. These are easy soils to work, but need plenty of manure and fertiliser. Parts of these counties and Tipperary, East Limerick, Kildare, east Galway, Laois, Offaly, east Donegal, Longford, Westmeath, Meath, Sligo and Roscommon, have medium-heavy loam soils. These are generally good, fertile soils, not quite as easy to work, but easier to keep fertile.
Counties Westmeath, Meath, Dublin, Roscommon, Longford, North Kildare, West Limerick, Clare, Cavan, Sligo, Monaghan, Tyrone, Fermanagh and Armagh, have clay loam soils that are heavy in varying degrees. Most of these soils are derived from glacial boulder clay. deposits and can be stony. They are fairly fertile soils, but often difficult to work and need high potash fertilisers.
In counties Sligo, Leitrim, Cavan, Monaghan, Clare, Fermanagh, Tyrone and parts of other counties, poor drainage adds to the heavy nature of the soil, making cultivation difficult and limiting growth.
Well SPOTTED
n There’s still time to join BirdWatch Ireland’s survey of garden birds, now in its 30th year. The data collected helps track the fortunes of our feathered friends now that gardens are increasingly a haven for biodiversity. Runs until end February, just follow the instructions on BirdWatch.ie.
WINTER BLOOMERS
n Why not pot up a few winter pansies – there is still time to do so and plenty of value and colour to be got from them in the coming months. At your garden centre now.
LUXE GARDENING
n Pick up tips on everything from composting to lawn maintenance as you explore the grounds of lovely Dromoland Castle on an inspirational weekend with head gardener Dorothea Madden and garden designer Arthur Shackleton. March 5 and 6, €490pp (based on two people sharing a room with both doing the Gardener’s Weekend). Includes two nights’ dinner, bed and breakfast; dromoland.ie
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