Gardener's Guide to Soil E-Book

Susie Holmes

• Herausgeber: The Crowood Press
• Kategorie: Lebensstil
• Serie: A Gardener's Guide to
• Sprache: Englisch

Seitenzahl: 157

Veröffentlichungsjahr: 2022

Beschreibung

The soil in your garden or allotment is the most precious asset you have as a gardener – healthy plants start with healthy soil. Written by two soil science specialists, this book explains the fundamentals of soil science in a horticultural context and provides practical guidance on how to optimize the soil in your garden.tThe main types of soil and their key characteristics are discussed, including the implications for different plants and how the soil can be improved, with an emphasis on working with nature, not against it.tTechniques for assessing soil health are described in step-by-step detail, with recommendations for ways this can be enhanced.tA detailed overview of the life in the soil, from bacteria to moles, shows how to harness this ecosystem and increase biodiversity.tThere is a chapter on container growing media tackles patio gardening and the use of raised beds. Finally, detailed examples from around the UK are provided to illustrate the scientific principles in practice.

Leseprobe

First published in 2022 byThe Crowood Press LtdRamsbury, MarlboroughWiltshire SN8 2HR

[email protected]

www.crowood.com

This e-book first published in 2022

© Susie Holmes and Neil Bragg 2022

All rights reserved. This e-book is copyright material and must not be copied, reproduced, transferred, distributed, leased, licensed or publicly performed or used in any way except as specifically permitted in writing by the publishers, as allowed under the terms and conditions under which it was purchased or as strictly permitted by applicable copyright law. Any unauthorised distribution or use of this text may be a direct infringement of the author’s and publisher’s rights, and those responsible may be liable in law accordingly.

British Library Cataloguing-in-Publication DataA catalogue record for this book is available from the British Library.

ISBN 978 0 7198 4091 3

AcknowledgementsThe authors wish to thank Louise Adams for the photos on pages 18, 34, 60, 72 and 88, Frank Ashwood for the photos on pages 64 and 65, Chris Cordwell for the photo on page 100 and the Royal Horticultural Society, Wisley, for the soil test documentation in Chapter 6.

Cover design by Blue Sunflower Creative

CONTENTS

1 Understanding Soil

2 The Physical Properties of Soil

3 The Chemical Properties of Soil

4 Organic Matter

5 Soil Biology

6 Assessing and Testing Your Soil

7 Growing Media for Containers

8 Simple Ways to Improve Soil Health

Glossary

Index

CHAPTER 1

UNDERSTANDING SOIL

The soil in your garden or allotment is your number one resource for growing plants, yet the importance of understanding it and improving its health is often overlooked. Having a knowledge of how your soil developed and its intrinsic nature will help a gardener to grow healthy plants in the best way possible. Many challenges to plant growth, such as adverse weather, pests and diseases, are less likely to cause major damage if the plant has a healthy root system – and a healthy root system can only develop in a healthy soil.

This chapter deals with how soils originate and the processes that are involved, because this will have a big influence on the type of soil in your garden. Resources for finding out more about your local soil types will be discussed and also the basic ways we describe soils and their properties.

Key Message for Gardeners

• Healthy soil means healthy plants.

• Understanding your soil and the life in it will help you get the most out of your garden or allotment.

• The soil is a gardener’s most precious resource.

How do Soils Form?

Soils have to start somewhere. The process of soil formation is very slow – it can take thousands of years for a few centimetres to form. Conversely, significant amounts of topsoil can be lost by erosion in only a few years under the wrong type of management. Looking after the soils in the world has never been more important and, even on a small scale in a garden or allotment, we can all do our bit.

Rock erosion by extremes of temperature and the action of water and sunlight is the first stage of soil formation.

Soils, with the exception of fully organic (peaty) ones, are produced by the weathering and erosion of the local rocks (geology). The ease of weathering of the rock depends on its geological origin and the climate in the local area.

The weathering agents are moisture, temperature (particularly the extremes and range between freezing and thawing), sunlight exposure and wind. All rocks can be weathered and will erode; the speed of weathering obviously depends on the severity of the conditions the rock experiences but also the initial hardness of the rock. A very hard rock (volcanic in origin), such as granite, will weather and erode much more slowly than a soft chalk (marine origin), and the difference in the breakdown of the rock into its primary components will give the soil many of the properties that we associate with it. Considering how many different rock types there are, combined with different climates, it is not surprising that there is a large range of different soil types both within the UK and globally. The first rule for a better understanding of your soil is to find what your type it is.

Key Message for Gardeners

The type(s) of soil in your garden or allotment will have a big influence on the types of plants that are most likely to thrive in it.

Finding Out About Your Local Soil Type

There are a number of approaches to learning more about the local soils in an area. One way is to find any geological survey maps for the location: for the UK and other some countries, this may be quite easy. The maps will usually show you the solid rock beneath your feet; however, the subsequent movement of material by ice, wind or water complicates matters so the type of ‘drift’ material overlying the solid geology is also important.

Simplified geological map of the UK.

Ice

In the UK much of the country as we know it was – until around 10,000 years ago – inundated by snow, ice and glaciers, which formed part of the last major ice age. As a result, many rocks were transported by glaciers as they moved across the surface. When the ice eventually melted, it left piles of ground-up rock (moraine), which may not directly relate to the underlying geology. If you are on the Lincolnshire Wolds, for example, your garden may well be on chalk as the solid geology, but it is just as likely that in the valley bottoms and the flatter areas south of the Wolds, you will be on a mixture of ground-up rocks moved here from different parts of the country.

Glacial moraines are the deposits left after the glaciers retreated at the end of the last ice age.

Wind

There are parts of the UK and central Europe where the main vector for soil movement was wind. For a sand to be wind-blown, the exact particle size is very important; given the correct conditions – for example, open fields with very little plant or crop cover – these particles can then be picked up by wind and deposited somewhere else. Specific areas of the UK such as the Vale of York, the Brecklands in Suffolk and soils around Western Park in Shropshire are dominated by wind-blown sands, which originated from somewhere out of the Ural mountain range.

The ‘brickearth’ soils of southern England are also formed from wind-blown sand, and these soils, combined with the local climate, were the basis for the development of the horticultural industry along the south coast of England. Well drained, and holding both water and air well, they can produce a longer growing season, so crops can be sown earlier in the spring.

Sands can be blown by the wind if there is little vegetation cover.

Water

The final, and in many cases most dramatic, erosive force in the development of soils has to be water. From racing upland streams to peaceful meandering rivers, water is always picking up and carrying rock and soil particles. At peak flows, larger pieces of rock and grit are moved, while in the slower, quieter waters, the material carried will be microscopic clay sediment. As the speed of flow slows, particles carried in suspension drop out and are deposited – sands and gravel being beached ahead of the alluvial fans associated with river mouths – creating the mudflats of the river estuaries. Along all river courses there will be varying soil deposits and, because rivers go through phases of directional changes and rejuvenation, there may well be mixed deposits in quite small geographic areas reflecting the river changes. This can lead to soils that in some areas are very clayey or silty sitting directly over sand and gravel deposits from previous river flows. The Severn River valley in Shropshire illustrates this very clearly.

Ox-bow loops on the River Severn, Shropshire – an example of sediment carried along by water and deposited where the water flow slows down.

Soil Maps

From the 1950s to the 1980s, the Soil Survey in England and Wales carried out soil surveys and mapped soils. When a ‘new’ soil type was identified it was given the name of the first place that the particular soil profile was characterized, and this was called a soil series. As an example, deep, silty ‘Hamble’ series soils formed on wind-blown fine sand deposits were first mapped around Hamble, near Southampton, but there are Hamble series soils in other areas, such as Kent, formed on a similar parent material. The Soil Survey of England and Wales produced six regional bulletins with maps for the main regions of England and Wales. They are now out of print but may be found in second-hand bookshops. Some areas were mapped in more detail, down to county or even parish level (mainly in areas with important horticultural production), and such maps may be available via vintage map sellers.

Another useful reference is the Cranfield University ‘Soilscapes’ map from the Land Information System (Landis; www.landis.org.uk/soilscapes). This has digitized information from the old soil maps and maps of England and Wales into twenty-seven main ‘Soilscapes’, or soil types, with general information about the typical soil texture, drainage and fertility of each Soilscape. It is possible to purchase a ‘Soils Site Report’ for the area around your postcode, which will outline the soil series in that area and their characteristics. It is important to remember, though, that in some areas soils have been disturbed or amended by previous land use so may differ from the original natural soils.

For Scotland, the James Hutton Institute has published soil maps for the main agricultural zones (mostly eastern and southern areas).

Table 1 Examples of some of the main soil types in the UK

Soil typeExamplesSandSuffolk heaths, Surrey heaths, Devonian sand, Vale of York, Western Park area of West MidlandsSiltLancashire coast, the Wash area of LincolnshireClayEssex/Hertfordshire chalky boulder clay, NorthamptonshireLoamEast Kent, Vale of Evesham, Sussex coastal plainChalk/limestoneKent and Sussex Downs, Cotswolds, Lincolnshire and Yorkshire WoldsPeatUpland peat soils in Wales and Scotland; lowland peat fen in Lincolnshire, Somerset, Lancashire Mosses, Solway areaMan-made/ brownfield soilsAreas restored after other land use; new housing developments with imported soil materials

Key Message for Gardeners

Do some research about your local soil types to find out their characteristics. The basic properties such as the soil texture (see Chapter 2) and chemical balance (Chapter 3) will have a significant impact upon what easily grows in your garden or allotment.

The Soil Profile

The physical matrix of a soil is made up of mineral particles of differing sizes, and these particles are split into three categories: sand, silt and clay. This will be discussed in more detail in Chapter 2.

Typical soil profile.

Soils are, however, not just about the physical matrix but also organic components. These comprise not only plant roots growing into the soils, but a whole range of soil life including insects, earthworms and microbes (for example bacteria and fungi), which live in the soil and are responsible for the breakdown of dead and decaying organic material into the physical matrix. For a gardener, the key to a healthy soil is nurturing the life in it, as this will in turn create a good root environment for plants. This will be covered in more detail in chapters 4 and 5. A vigorous, healthy root system helps the plant obtain water and nutrients from the soil more effectively and fight off attack from pests and diseases.

The result of the breakdown of organic material is that the soil has a whole series of organic components added to it that help to glue or cement the physical particles together and result in what is termed the ‘tilth’ of the soil. The colour of the soil is a good key to how healthy it is – red/brown colours are seen in healthy soils because there is plenty of oxygen present whereas anaerobic, waterlogged clays tend to be more grey/blue in colour.

Soil structural units.

Soil tilth can be thought of in terms of the development of structural units in the soil profile. In a healthy, biologically active soil profile with lots of earthworm activity, the structure in the topsoil (A horizon – see below) will be formed of small units of soil, well rounded and with plenty of air space between the units for both gas exchange and water movement. This type of topsoil will create a good environment for seeds to germinate and seedlings to flourish. In a compacted or cloddy topsoil, seeds may fail to germinate if they dry out due to large air gaps and insufficient moisture, or rot off if the soil is too wet because it doesn’t drain. Smaller seeds, such as lettuce, will be more susceptible to poor seedbed conditions than larger seeds such as broad beans.

If we examine a normal soil profile to 90cm (35in), what we normally see is at least three distinct, colour-separated layers or ‘horizons’. These are normally labelled as the A, B and C horizons. A is called the topsoil and is normally the darkest colour with the greatest degree of organic matter and biological activity producing the greatest degree of tilth, and C is normally taken as the ‘parent material’ of the soil profile – relatively untouched by biological activity – although there may be deep plant roots and earthworm burrows.

The B horizon, or subsoil, is the interface between the topsoil, where the main biological activity happens, and the parent material in the C horizon, so it shows some colour changes from the parent material and there will be some development of larger structural units. The structure of the subsoil will have a large influence on how well surface water drains through the soil profile. Even if you have managed to produce (or buy in) a well-structured topsoil, if it is sitting over compacted subsoil, rainfall will not percolate through and waterlogging can result.

Healthy, well-drained soils have warm brown/orange colours with lots of earthworm activity.

Poorly structured soils have dull brown/grey colours due to poor drainage and waterlogging, and little or no earthworm activity.

Of course there are always exceptions to rules, and some soils will have topsoils with sharp angular structural units and be more of a grey to very blueish brown in colour. The B horizon in such profiles may have a distinct boundary to the topsoil, rather than merging with depth, there will be an obvious lack of earthworm activity and the structural units will be large and angular – and in the wetter months it may be impossible to see them clearly. The colour of the B horizon may be a contrast between blue/grey and bright red/orange on the cracks. This tends to indicate a very poorly drained soil, perhaps due to high clay content or a water table that is close to or fluctuating near the surface.

Soils that are naturally not well drained are better suited to long-term planting, such as lawns or meadow areas or shrub borders, rather than intensive vegetable growing. Many grass and meadow species can tolerate even some surface ponding of water over winter; they may die off but will re-shoot in the spring when the soil dries out.

Key Message for Gardeners

It is helpful to understand the nature of the subsoil in your garden as well as the topsoil layer because that will dictate how well the soil drains and if deeper-rooting plants, such as trees, will thrive.

Key Message for Gardeners

If your soil has a naturally weak or compacted structure the drainage will probably be poorer and plants that do not tolerate these conditions may struggle even if you can improve it, especially if you are in a higher rainfall area. Try to choose plants that are adapted to your local soil type rather than battle against it – look at what is growing well in neighbouring gardens!

Organic Soils

The other great exception to the rule is highly organic soils, which may exist if the garden is in a floodplain or has a naturally boggy area or a spring. In these cases, any accumulating organic matter has no real chance to decay and the major biological elements, such as earthworms, may be missing. In this case the A horizon becomes a black accumulated mass of organic material – somewhat like a sedge peat layer. These soils are rare in gardens but do provide opportunities for unusual plantings of bog plants. The B horizon may be almost completely distinct from the A horizon – in some cases it will be alluvial silts and clays from the floodplain. These soils will be naturally poorly drained and inundated with water for many months at a time.

Bog garden plant communities thrive on waterlogged soils that would not be favourable for many other plant species.

Soils on New Developments

In many new-build housing projects the job of the garden development is contracted out. The original soils in the area will have been stripped prior to building commencing. The subsoil and topsoil often get mixed during this process and if the soils are moved when wet the structure is usually badly damaged so that even a good-quality soil can end up with compaction by the end of the stripping/storage/spreading process.

Soils in new housing developments may be the ones originally present on the site or may be imported from elsewhere; either way, they are likely to have suffered damage to their structure due to movement and storage operations.

Raised beds are an option where the soil is very poor, badly drained or shallow in depth and are particularly useful for growing vegetable plants in allotments and community gardens.

The result is that the plot of garden is often made up of a stripped material (parent material), which is then covered by an imported ‘topsoil’ from another area or manufactured topsoil. The soils are likely to have suffered from compaction due to movement and trafficking by heavy machinery. This may well mean that the soil in the new garden does not conform to any of the classic geological patterns described above and there may be a complete discontinuity between the imported topsoil and the underlying layers.

In such cases it may well be better to avoid traditional gardening practices such as double digging, but to start initial planting in newly created raised beds or in containers while you gradually improve the soil. Container growing media are discussed in Chapter 7.

Summary

• Soils are generally the product of weathering and erosion of primary rocks, with the particles then further sorted by either wind or water.

• The soil in your garden is your number one asset, so finding out about the type of soil you have will help you learn how to manage it and keep it healthy.

• The health of the soil is related to the soil life and organic matter level and also the degree of waterlogging.

• Fully organic soils are rare in gardens but occur where organic matter accumulates under extremely waterlogged conditions.

•