Topsoil is quite literally the “top soil”, the upper layer of soil which is defined as the first two to twelve inches of soil (regardless of which of the many soil types it is) and is measured from the surface to the first densely packed layer of subsoil.

This top layer, also known as surface soil, is where the majority of plants lay most of their roots; they generally do not extend their roots lower than the topsoil layer because it contains an abundance of microorganisms, organic matter, humus and nutrients, basically everything they require to thrive! The nutrients in the soil dissolve in water making it easy for roots to absorb.

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.

What is…

  • Organic Material

    Organic matter is what is left after plants and insects die. Part of the reason why the topsoil has the highest concentration of nutrients, above all other layers of soil, is that this is where organic life decomposes upon death. The nutrients are returned to the topsoil from where they originated hence why it is usually also darker in colour.

  • Subsoil

    Subsoil is the layer (or stratum) of soil directly below topsoil. It’s composed of a variable mixture of small particles such as sand, silt, and clay, but whilst high in minerals like iron, aluminium oxides, and calcium carbonate it has a much lower percentage of organic matter and humus. Subsoil tends to be paler than its overlying topsoil due to the lack of dark humus. This hidden soil layer is directly affected by water movement. Minerals from the topsoil find their way down into the subsoil through water runoff. As a result, topsoil can have mineral deficiencies which force some plant and tree roots to dive deeper for nutrients while allowing them to establish themselves deeper in the soil structure.

  • Humus

    Humus is dark, organic material that forms in soil when plant and animal matter decays. The thick brown or black substance that remains after most of the organic litter has decomposed is called humus. Humus contains many useful nutrients for healthy soil. Earthworms often help mix humus with minerals in the soil.

Types of soil on the market

Economy

This topsoil tends to be supplied “as dug” meaning it is in its most basic form straight from the ground. It is unscreened and therefore will be a mixture of both large and small soil particles and extremely likely to contain weeds, roots, stones of varying sizes and other debris or foreign objects. This topsoil is cheaper because it has not been screened or refined so it is commonly used to build up areas where volume rather than quality is required. This type of topsoil is ideal for when optimal growing conditions are not necessary. For example, jobs such as levelling, hole filling or to support a raised bed wall.

General Purpose

This type of topsoil is as the name suggests, generally suitable for a wide variety of garden purposes. In all likelihood it will be screened and can be purchased in different screen sizes dependent on the project at hand, with more coarse grades suitable for turf laying and finer grades more useful for top dressing lawns. This type of topsoil is also useful for making new beds and borders, as well as making an excellent base for the sowing of new lawns.

Premium

Though it can be expensive, premium grade topsoil is most definitely screened and of high quality. It should be free of any (or at least very few) weed seeds which is beneficial for those tending to the garden. This type of topsoil is extremely high in fertility and has a good structure, so is often used to build up flower borders or even create entirely new beds for flowers and other plants. Nurseries often use this type of topsoil in compost mixes for plants grown in containers.

Screened topsoil is a process where the soil is filtered through a mesh (picture a very large sieve!) in order to remove stones and debris from the soil. Customers can choose how fine or chunky they want the topsoil to be depending on what it will be used for. For example, a screened ton of topsoil sold as screened to 10mm means there will be no stones or debris in the soil over 10mm (1cm) in diameter. The benefit of screened topsoil is that it is a consistent size which allows for optimum water flow and distribution of essential nutrients which will keep your garden healthy.

Unscreened topsoil does not go through the meshing process so it tends to be coarser and more uneven. It is therefore a cheaper alternative and as can be expected doesn’t provide the same quality and benefits as the screened topsoil does.

What is BS 3882:2015?

The British Standards Institute (BSI) has published a British Standard for topsoil – BS 3882:2015. The standard is a guide for the provision of topsoil and can be used when ordering topsoil materials.

View our selection of soils here.