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Quite literally, it is the 'top soil' on the outer layer of the Earth's surface, usually between 2 and 12 inches (5 - 30cm) deep. The depth of any topsoil can be measured from the surface to the first densely packed soil layer commonly known as subsoil.
Topsoil is created naturally through a slow process of weathering rocks and decaying organic matter causing them to break down into very small parts. Typically, it takes around 100 years for every inch (2.5cm) to be formed.
This top layer is where majority of plants lay most of their roots because the high concentration of organic matter (including the three main groups - humus, clay particles and sand) and important minerals allows them to absorb nutrients and grow healthily.
Among other things, topsoil can contain:
Topsoil can vary in colour, content, texture and pH level. Depending on the area you live in, it may be more alkaline or acidic. A good quality topsoil should have a pH value of between 5.5 and 7.5 - mildly acidic to slightly alkaline - to ensure most plants are able to absorb nutrients from the ground.
Although there are many different soils, they can largely be classified into six structure types:
Each soil has its own unique properties and are best for different situations.
A clay structure soil is heavy and benefits from high nutrients. It's made up of very small particles with spaces between them which means the soil holds a high amount of water, drains slowly and takes longer to warm up in the summer.
To be classified as clay soil, it needs to be made of over 25% clay. Typically, clay soils remain wet and cold in winter (making them prone to water logging) and dry out in the summer, often causing them to crack. The best plants for clay soil are trees and the hardier varieties of perennials.
Sandy soils are characteristically light and dry due to their high proportion of sand and small amounts of clay. These soils have quick water drainage and are easy to work with; however, they're low in nutrients because the rain tends to wash them away.
It's made up of the largest particles among the different soil types and is quicker to warm up than clay soils, but also tends to dry out in the summer. It's best to use a sandy soil for plants that don't need lots of water - for example, evergreens or sumac.
Silty soil has much smaller particles than sandy soil, but larger particles than clay soil. As a result, it's able to retain water for longer, but also drains poorly. Despite this, it's considered to be among the most fertile of soils.
Soft and smooth to touch, silty soil can compact easily which decreases its ability to infiltrate water in wet periods, so it's important to avoid trampling on it when working on your garden or landscape.
Peaty soil is rich in organic matter and able to retain a large amount of moisture. Originally formed over 9,000 years ago with the rapid melting of glaciers, peat soil benefited from drowned plants dying quickly and slowly decaying underwater leading to the accumulation of organic matter in a concentrated spot.
It's rare to naturally find peat soil in a garden, it often needs to be imported to regulate soil chemistry or pH levels to provide an optimum soil base for planting. As well as its ability to hold water in the dryer months, it can also protect roots from damage during very wet months.
Chalky soils can be either light or heavy, but they are always highly alkaline due to the calcium carbonate or lime within its structure. While they are very fertile, many of the nutrients are unavailable to a selection of plants (ericaceous) that require acidic soils to grow.
Organic matter decomposes fast and it's very free draining with minimal water retention which often causes chalky soil to dry out easily. It will often be obvious to spot chalky soil because there will be visible white lumps. However, the soil might still be alkaline without visible chalk. To test your soil, take a small piece and drop it into a jar of vinegar. If it froths up, the soil is alkaline.
Although not strictly a soil of its own, loam is made up of three main types of soil: clay, sand and silt. Depending on their predominant composition, they can be either sandy loam or clay loam. It's important to remember that all loam is topsoil, but not all topsoil is loam.
Loam soil is often viewed as the ideal soil because it's a mixture and avoids the negative effects of each of its components. It has excellent water and organic matter retention, but also drains well and allows air to move freely between particles down to the roots.
The list of uses for topsoil is quite extensive, but it is largely used to create plant beds, repair lawn damage and improve soil drainage as well as improving the quality of the soil and levelling out uneven grounds or lawns.
Mixing top soil with existing soil helps to create a transition layer that helps to prevent drainage problems between the two soil types. When creating plant beds, you also want to add an extra topsoil layer on top.
Topsoil can also be used to fill in holes, dress bare areas and level out uneven ground. Using a sandy topsoil in an area of lawn or garden that tends to hold water can help to improve the location's drainage and provide subsequent growing success.
Using the right type of topsoil on your land will provide plants and flowers with the right kind of nutrients to flourish. The rich soil is packed with good nutrients, minerals and organic matter to provide a source of food which should allow anything you plant to grow well.
However, there are occasions where topsoil is not the best material to be used. If you're growing plants in pots or other restricted areas, topsoil fails to provide enough nutrients; it is best utilised where plants can spread their roots. In this instance, compost is a better growing medium.
You can mix compost with topsoil to create your own potting compost which is the tactic that many nurseries do because it combines the advantages of soil with the benefits of compost.
Topsoil is available in three grades: economy, general purpose and premium. These classifications are largely based on how fine the soil is and the quality it provides in terms of allowing plants and flowers to flourish.
Economy grade topsoil, also referred to 'As Dug', is the lowest grade and will not have been screened, so is likely to arrive containing rocks, stones, sticks, weeds and roots. It is usually very cheap which makes it perfect if you need to fill large areas and quantity is more important than quality.
As the name suggests, general purpose topsoil it suitable for most garden projects including making new garden beds and laying a new lawn. It is ideal for landscape gardening due to its nutrient richness and ability to build up contours in an area of land.
Unlike economy grade topsoil, it will have undergone a screening process so that it is suitable to grow plants and flowers. You can buy general purpose topsoil with larger or smaller grains to suit your project. The finer ones are best for top dressing lawns, while the coarser examples are better utilised laying lawns.
Premium grade topsoil is the best quality available and should be free of any weed seeds. Also known as certified soil, it has been lab tested to ensure it is free from any metals and diseases.
If you want to grow vegetables or flowers for shows, you should use this top quality topsoil which is particularly rich in nutrients. It can also be used for delicate seed beds and young lawns needing encouragement to grow.
As an alternative to buying better topsoil, you can try to improve your existing topsoil by adding soil improvers and organic composts. To get the best results, you need to know what type of topsoil you have. You can try the sausage test or pick up a testing kit from most garden centres.
The most effective method to braking down clay soil is by raking it with manure. It helps to 'open up' the soil which, in turn, improves drainage and fertilises the soil in the process.
As explained earlier, sandy soil doesn't retain water well which often causes nutrients to be washed away. To combat this, you can add mulch on top which will gradually break down into the soil fertilising it and helping it to hold moisture. It will also prevent and reduce weed growth as an added bonus.
Usually, topsoil is sold in bulk and can be purchased from garden centres, home improvement stores and online from selected suppliers.
Here at Wiltshire Grab Hire we provide certified, screened and 'As Dug' topsoil from our own aggregate production facility. We can supply any product from 10 tonnes to several thousand tonnes depending on your project.