3. The secrets of the soil

3. The secrets of the soil

Suggested timing: November/ December

In the last section we looked at the Mystery of Growth. The growth of plants is dependent on the soil in which they grow. The health of the soil, and so the health of the plants that grow in the soil, depends on the incredible relationships and interactions which take place between the living organisms in the soil.

Short film: The Secrets of the Soil


By the end of this section, you will enable children to:

  1. Understand the structure of soil
  2. Learn about chemical processes in the soil
  3. Discuss different factors affecting soil quality (erosion, vegetation, carbon matter, climate)
  4. Be aware of different soil types
  5. Reflect on how soil is used

1. What is soil?

Soil is a generic term referring to the land on which we walk, build roads and houses, and grow our food. However, soil is more than just a ‘flat surface’… there are different types of soil and a lot more happens under the ground than we may suspect.

Activity 1A: The meaning of 'soil'

In class, children may be encouraged to give their ideas of ‘soil’. They may refer to a one-dimensional idea (for example ‘surface’), or they may use common words to talk about the ground (for example, land, floor, ground or earth).

Activity 1B: Observing soil

Different soil samples can be made available for children to observe, manipulate and discuss – these may include sandy, silty, and clay soil types.

Useful resources

2. Soil uses

Why do we have so many words to talk about soil?

Activity 2A: Talking soil

Teachers may help children to reflect on the different uses of soil, and materials derived from soil (this might include growing, building houses, and transport), also the importance of soil for human beings and other living things. What would happen if there was no soil?

Useful resources

3. Soil types

The word ‘soil’ is used to describe a section of the earth with particular qualities. Soil types are different from each other depending on:

  • What they contain
  • Their structure
  • Where they are found (climate and location)

Soils can change over time depending on all these factors.

Activity 3A: Soil sampling

Outside: children can continue mapping the school grounds by taking soil samples from different locations. Each sample needs to be labelled clearly and stored in a small container, and the location where the sample was taken from should be marked on a map (equipment needed: selection of small plastic containers, shovel, map of the school grounds).

Indoors: children can compare their different samples and organise them by colour, wetness, and texture.

Useful resources

4. Water retention properties

Soil ‘type’ is influenced by many factors, including its ability to retain water.

Activity 4A: Testing the ability of soils to retain water

Different types of soil retain or release water, depending on the ratio between the solid rock content (which provides drainage) and clay/organic matter content (which retains water). The mason jar experiment (see resource links) helps visualize the amount of different soil particle sizes, sand, silt and clay, in the soil.

Activity 4B: Question time!

What happens if all plants are taken away from the soil? What happens if too many plants are planted and harvested too often? Answering these questions leads to discussion about:

  • Soil erosion due to deforestation
  • Salty soil due to water being pumped out of the ground in excessive quantities (for example, for large-scale irrigation elsewhere)
  • Soil exhaustion, when the soil is overused
Useful resources

5. Healthy soil. Exhausted soil.

Soil needs to be cared for. Soil exhaustion happens when it hasn’t been properly looked after and the soil is no longer able to support the growth of crops or other plants. Managing and caring for soil can include:

  • The addition of calcium carbonate (for example fishbone meal) into the soil to raise the pH to a suitable level for the crop
  • Ensuring the soil is airy and not compacted - airy soil can help the roots to breathe and supply energy for the plants to grow. Worms help with turning soil around and letting air into the ground
  • Crop rotation
Activity 5A: Setting up a mini wormery

To show how worms help to mix soil and bring organic material down into the soil, you can set up a mini wormery (see Useful Resources).

It’s a good idea to test the pH of your soil (how acidic or alkaline it is) as different plants grow better in different soil pH’s.

Useful resources

6. The soil at rest

In winter, produce is available to us in preserved forms (frozen, tinned, dried, pickled, stored), or in jars under vinegar or oil. However, by planning ahead there are also crops which can be ready for winter harvesting. Additionally, while there may not be a lot growing in the garden over winter, there are still plenty of jobs to do (see resource links).

Activity 6A: Storing and preserving produce

Children can research the ways in which to store or preserve excess produce from the garden if there is surplus that cannot be given away, or if some is to be kept for the winter months – see Useful Resources for some ideas.

Activity 6B: Growing for winter harvesting

Investigate which crops can be planted to be ready over the winter months in your local area. Plan these into your growing calendar (see Useful Resources).

Useful resources

You have reached the end of this unit. To assess your knowledge before starting the next unit, please complete the short quiz found at the link below.

Please note: you will have to enter your email address at the start of each unit quiz if you wish to be sent a Garden Schools Certificate of Completion once you have worked through all 8 units and quizzes.

Complete The Secrets of the Soil short quiz