A short guide to garden soil

For a gardener, the garden soil is probably the single most important thing in your garden.

Everything good in the garden comes from the soil, so it’s important for gardeners, especially new gardeners, to understand their soil – we need to know the characteristics of the soil we have and we need to know how we can improve it, if necessary.

In this video you’ll find an introductory guide to garden soil covering the following topics:

  • What is soil?
  • Why does soil matter?
  • Soil texture
  • Soil structure
  • Improving soil

A short guide to garden soil

Here is a summary of what is in the video.

What is soil?

Soil consists of 5 elements:

  • Mineral (rock) particles
  • Organic matter (humus, decaying plants and animals)
  • Water (soil solution)
  • Air, and
  • Living things – insects, microbes, viruses.

Why does soil matter?

The type and quality of the soil you have determines which plants you can grow and also how well your plants will grow.

We can see this in nature because, along with factors such as climate, the quality of the soil can mean the difference between a lush green landscape and a barren scrubby one.

Soil texture

All soil is not the same. Soils from different locations, even locations quite close to each other, can differ widely.

This is because:

  • In different types of soil, each of the five soil components mentioned above are present in different proportions
  • In different places, the mineral particles which make up the soil are derived from different types of rocks
  • Different plants and animal matter are present
  • Different processes of soil formation may have taken place, e.g. weathering or water erosion.

Soil texture is the central characteristic which varies between different soils. It is basically a measure of the size and proportions of different particles in the soil, that is the relative proportions of sand, silt and clay particles.

Soil texture can be described on a continuum between sand and clay, from sand through loam to clay. Thus the texture of an individual soil will be determined by the respective amounts of clay and sand content.

What difference does soil texture make?

Different soil textures give rise to different characteristics in the soil.

Sandy soils are open textured and free draining, so do not hold water or nutrients well,

Clay soils are closed textured, can be come sticky and waterlogged when wet and set hard when dry.

This is important to gardeners because all plants prefer the characteristics of particular types of soil.

For example, plants like succulents, cacti and many Mediterranean plants such as lavender and rosemary, need free draining soil. If you planted them in heavy clay they would not thrive and would probably die.

Other plants, such as potatoes, bananas or bamboo require heavier, richer soils that are more water retentive.

Most plants, e.g. Thalictrums or Dahlias like moist but free draining loams. If you have soil of that type, you can grow almost anything.

Garden soil: lavender requires free draining soil
Garden soil: lavender requires free draining soil

Soil structure

Soil structure is also a fundamentally important characteristic of soil.

Soil structure is how we describe the way that all the various components of soil are combined. Generally, soil components combine to form aggregates or crumbs, with spaces in between.

The existence of these crumbs and the sizes of them determines the type of soil structure in place.

Good soil structure

Good soil structure:

  • Has small crumbs, well bound together that do not break up when wet or when dug
  • Has lots of spaces and channels between crumbs so that water and plant roots can penetrate
  • Allows air into the root spaces
  • Allows roots to grow easily
  • Allows water to be made available to roots but also to drain away.

Poor soil structure

Soil with poor structure:

  • Lacks small crumbs or aggregates
  • Is hard and compacted or consists of large lumps
  • Cannot be easily dug, but may be eroded by rain water or wind
  • Means plant roots, air and water cannot easily penetrate.

Improving soil

Whether soil is sandy or clay, you can always improve soil structure with the addition of plentiful organic matter – compost, leaf mulch etc.

Sandy soils can be improved with the addition of clay topsoils.

Clay soils can be improved with substantial amounts of sand or grit, or sometimes with gypsum.

Improving garden soil is an ongoing process for gardeners and is a big subject in itself that will be covered in more detail in future posts.

Remember, nurture your soil it and it will repay you well.

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