The Importance of Choosing ‘Safe’, Fertile, Consistent Topsoil

Topsoil is an important, fundamental resource. Without it the human race could not exist. We rely on topsoil to provide a growing medium for all our food and environmental resources. Living matter – plants, trees and grass cannot sustain or survive without it.

Topsoil layers or ‘horizons’

Soil, naturally, is separated into layers called horizons. These horizons are described as topsoils and subsoils. Topsoil material is generally darker due to the impact of the organic matter that has incorporated itself within this layer. This organic matter is also responsible for enhancing the physical properties of the soil such as tilth, structure, water infiltration and water holding capacities.

The topsoil horizon plays a major part in plant growth and biological diversity as well as some hydrological processes. Topsoil is the interface of air, minerals, water and life (soil organisms), which all interact with one another to support and maintain a soil structure.

The four major components of soil are air, water, mineral matter and organic matter. The relative proportions of these components greatly influence the behaviour and productivity/performance of the soils. The proportions of mineral particles in these different size ranges are called soil texture.

Identifying good soil texture and structure

Terms such as loam, sandy loam, silty clay and clay loams are used to identify the soil texture. Soil texture can also be influenced by the amount of organic matter (OM) present and the form in which it derives. OM is important for good soil structure as it aids aeration, infiltration and increases the soil’s capacity to hold on to nutrients and prevents the soil from being eroded.

Soils need an open structure in order to function as a growing medium. In particular, it influences the main soil and plant root functions – aeration, drainage and root development. Without structure, soils will suffer from anaerobism (lack of oxygen), water logging and nutrient lock-up and, ultimately, plants will wither and die!

Check topsoil colour. Generally, light coloured materials have lower organic matter contents than dark brown or black soils.

The other elements found in topsoil that influence plant growth are soil pH and nutrients. pH is an indication of the acidity or alkalinity (basic nature) of soil. A pH of 7.0 is neutral, while values below 7.0 are acidic and values above 7.0 are alkaline. The pH of a soil will impact on the plants ability to feed on the nutrients within the soil.

Guidelines for soil pH

A topsoil suitable for multi-purpose landscaping as per the British Standard BS3882:2015 should have a pH between 5.5 and 8.5.

What to consider when selecting topsoil:

  • Where does it come from?
  • What is the nature of material in that area generally?
  • How was the material excavated, stockpiled and transported?
  • Does it achieve the British Standard?
  • How much material do I need? Calculate the cubic volume by multiplying width x length x depth.
  • What are the likely costs and delivery charges?
  • When do I want it?
  • Can I afford to accept substandard materials?

Overview of the British Standard

The British Standards Institute (BSI) has published a British Standard for topsoil – BS3882:2015. The standard provides a specification for a multi purpose general purpose landscaping topsoil.

The standard covers the following:

  • Description of topsoil
  • Texture
  • Soil reaction (pH)
  • Stone content
  • Contamination testing

The standard is a guide for the provision of topsoil and can be used (if applicable) when ordering topsoil materials. All of this information will tell a lot about the soil and its current condition.

How to source reliable topsoil

Topsoils can be sourced from many suppliers. It can come straight from a site or it can be sourced from stockpiles of materials. Care should be taken when sourcing from old stored soil piles, as the soil may have become de-structured.

Most companies will screen their topsoils, putting them through sieves to ensure that they are uniform in size on delivery and able to meet your specified requirements. Also, most companies are able to mix different soils to achieve a required specification.

Topsoil is now becoming an expensive commodity, and can cost in the region of anything between £50-£200 per tonne if collecting from the supplier. A number of factors will dictate these costs, what it is being used for, importantly source of material, soil quality and soil type; the amount required (bulk or bagged) and haulage charges.

Removing and re-laying topsoil is an expensive operation both in time and money. It pays dividends to establish the quality of any materials prior to use. Prevention is better than cure.

Questions you should ask your supplier:

  • Do you sell it in bags?
  • What size deliveries can you make?
  • How quickly can you deliver?
  • What are you delivery charges?
  • Can I get hold of your soil all year round?
  • How much have you got?
  • What can it be used for?
  • Does it meet British Standard 3882?
  • Are soil analysis certificates available on request?
  • Is it safe for use? How can you prove this?
  • Is it free of contaminates?
  • Where is it from?
  • What is in the soil?
  • What are the delivery terms and conditions?

It is vitally important you know what you are receiving. Topsoils can also be altered in many ways, many soil suppliers have the facilities to screen, blend, amend and mix topsoil materials to produce a wide range of variable rootzone products that are generally used for top dressing and planting purposes.

Remember to ask for a breakdown of the materials being supplied and, more importantly, how consistent these materials will be, and have they enough material to complete the job/task?

Always deal with suppliers that give a full back up service based on factual evidence of the efficacy of their product, not the ‘Honest Johns’ that give a cheap product matched by cheap or non existent back up. After all, the cost of digging out a substandard material and replacing it with the real McCoy can end up being a lot more expensive than that initial ‘saving’!.