Natural Topsoil and Topsoil Substitutes

In today's landscape industry, there is a choice of Natural Topsoil (soil derived from the upper layer of Greenfield sites) and Blended (Manufactured) Topsoil (topsoil formed when two or more components are intimately mixed to form a growing medium).

There is an on-going debate about the pros and cons of topsoil substitutes, and whether they are better or worse than natural topsoils. There is no definitive answer to this, as both 'natural' and 'manufactured' topsoils can vary in composition, depending on the site's geology, etc. (natural topsoil) or the components used to make a topsoil substitute.

At first glance, it may appear as if nothing could be better than natural topsoil. However, as previously mentioned, the composition of natural topsoil's can be variable and some are simply not suitable for landscaping. Another reason why natural topsoils are not as preferable as the manufactured alternative is, inconsistent availability.

Natural topsoil is derived as a by-product of 'Greenfield' development. It is not quarried like sands and gravels. When Greenfield sites are developed for housing, business parks, highways, etc, the topsoil is stripped off before construction commences, and any surplus topsoil is taken off site for re-use on other landscape projects. As a consequence, the availability of natural topsoil can be inconsistent, as it generally only becomes available in any area at the time of a topsoil strip.

In many instances, topsoil substitutes (manufactured topsoils) provide as good as, if not superior alternative to natural topsoil, as long as the correct components have been selected and blended in the correct manner. The attributes of topsoil substitutes include a consistent composition, a greater availability and an absence of perennial weeds and potential contaminants.

However, the exact opposite can be the case where inappropriate soils or composts are used, or the blending process does not have the necessary control measures to ensure a consistent mix. For example, 'Skip waste soil', which is derived from Brownfield site clearance operations, is not usually suitable as a component for manufactured topsoil. This material is usually extremely alkaline, saline, and deficient in organic matter and plant nutrients. It can often have elevated levels of zootoxic and phytotoxic contaminants and contain 'sharps' e.g. glass and metal.

At the end of the day, the most important aspect is that the topsoil selected meets the functions of a 'growing medium' and the specific requirements of the proposed landscape scheme.

Topsoil with excessive concentrations of Potentially Toxic Elements (PTEs), can be hazardous to human health and the environment. It is therefore essential to ensure that the soil is SAFE, particularly if it is to be used for sensitive end uses, such as domestic gardens, public open spaces or allotments. A reputable topsoil supplier should be in a position to satisfy you that their topsoil is fit for purpose.