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Loam Soils in the Garden.


The term ‘loam soil’ often bemuses gardeners and is rarely described, but often used with planting instructions for certain plants. Most garden plants it seems prefer to be planted in loam or fertile soil.

There are several definitions as to what constitutes a loam soil, but most agree that loam soils are generally made up of near equal parts of clay, sand and silt particles – generally a smaller ratio of clay particles. Those are the important ingredients that define a loamy soil.

Each of the mineral constituents has an important part to play in the makeup of this desirable growing medium. The properties of loam soils are dictated by the actual mineral fragments of sand, silt and clay.

If you were to do our suggested basic soil type test, a loam would would be similar to the diagram above.

  • The sand particles allow for free drainage and open texture; sandy soils are free draining
  • Clay as a binding agent that is also water retentive; Clay soils notoriously difficult
  • Silt is the in-between particles which is important for filling in the gaps and aiding fertility generally
  • Organic matter completes the mix with its ability to hold soil moisture and nutrients and provides the basics for actual soil fertility. Without organic matter, we have mineral earth, rather than soil!

Diagram of loam soilsLoam Soils Classification

Loam can be further classified as clay loam; sandy loam or even a silt loam The different definitions being brought about by one of the mineral particle ratios being higher.

The individual particle sizes of clay, silt and sand are....

  • Sand Particle size falls between 0.05 mm – 2 mm. Distinctly abrasive when rubbed in the hand. Any soil particles larger than that are classed as gravel (2 mm to 75mm) Larger than that are rocks!
  • Silt Particle size 0.002 mm – 0.05 mm – slightly gritty when rubbed between fingers.
  • Clay Particle sizes less than 0.002 mm in diameter. Individual clay particles are virtually impossible to separate with the human eye, feeling smooth and silky (if moist) when rubbed between fingers.

That’s a good start for the definition insofar as the physical characteristics of the mineral earth particles are concerned, but we gardeners also need that all important ingredient of fertility - organic  matter. Organic matter – as important as it is – does not help to classify a loam soil. For instance it is possible for clay, sandy, or silt soils all to have a similar content of organic matter or humus.

Characteristics of Loam Soils

Soil particle size and ratios as above are the important ingredients which give loam soils their characteristics of open textured, easy to work, fertile soils. The fertility of loam soils is determined by the additional all important ingredient of organic matter and soil nutrients.

Advantages of Loam Soil

One of the biggest advantages of a loam soil is the fact that almost any plant will grow in it - providing it meets the criteria of ph. levels. Add to that, loam soils are almost always easy to work with - being easy to manage underfoot and also easy to cultivate.

This ‘all-purpose’ property of loam soil made it an obvious choice for the soil scientists at the John Innes Institute, when they set about formulating a range of composts that would suit the majority of plants to be grown in their now-famous JI Potting composts. It was quite specific in stipulating that loam soil should be the basis of the universal composts.

Providing that the loam soil also contains adequate organic matter – which in itself is not a pre-requisite for determining whether a soil is loam or not – the widest possible range of plants will be happy to grow in it. Its natural advantages being that it is

  • Open textured and free draining
  • Normally retentive of soil moisture and therefore soil nutrients do not readily leach out of the soil.
  • Loam soils are much easier to work and cultivate than clay-type soils.
  • More conducive to fertility than sandy soils.
  • More suitable for growing a wide range of plants
  • Best for including as a soil base in container gardening composts.

Whilst it has all the advantages listed above, it still needs proper management in the garden, which will include additions of compost and fertilisers, and also additional watering from time to time.

Loam soils develop over many years – centuries even and are dependent upon many physical and geological factors. You cannot (without huge upheaval and investment) turn a clay or sandy soil into loam. The best you can do is to improve other soils – mainly by the addition of organic materials and proper cultivation methods.

If you are blessed with a loam soil, nurture it, for it will provide you with a good start to your gardening success.



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