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Topsoil – what is it, and where to use it

Date: Tuesday, 07th Sep 2021 | Category: General

The Real Soil Company is here with some handy advice on something you can’t win the gardening campaign without: topsoil.

This is the soil which forms the top layer of ground in which plants grow. It is a varied mixture of minerals and organic materials which gather on the surface of the ground and become nutrients which support the life of whatever grows in it. We took a look at a few of the most common uses of topsoil to help get your growing projects off to a flying start this Spring:

Grow Bags and Planters

Many people dipping their toe into grow-your-own will start off with herbs and veggies in grow bags or planters, which are easy to access from their kitchen windowsill, balcony or outside the back door.

Plants in containers need a bit of extra nutrition compared with those in open soil where roots can spread further, so first add some super-rich organic compost to the planter or grow bag before filling up the rest with nutrient-dense, peat-free organic topsoil. As a general guide, it should be 1 part compost to every four parts of premium soil, depending on the specific plants to be grown. Plants which thrive in acidic soil can take more compost than those which prefer alkaline conditions.

Raising the Stakes

If you’re already past the grow bag stage, the chances are you’ll be thinking of making a few raised beds, which are a great way to organise gardens and allotments. Raised beds not only help with both soil temperature and drainage, but also provide a frame you can fill with enriched topsoil that provides optimum growing conditions for your greens.

The minimum depth of a bed should be eight inches (20cm) but some plants, including root vegetables, will need up to 24 inches or 60cm of soil to grow in. If you are placing the bed on a hard surface it should beat least 16 inches (40cm) to ensure the roots of your plants won’t hit concrete or some other unyielding material.

If you’re placing the bed on existing earth or turf, first mark out the area and clear it of grass, weeds and other vegetation to the required depth. You can then stake out the corners with timber posts that should be pushed to a depth of at least 12 inches.

When it comes to construction of the side walls you can be quite creative and look at either new or reclaimed materials but, if you decide on timber, make sure it hasn’t been covered in a chemical preservative. If in doubt, you can line the inside of the bed with allotment sheeting to stop chemicals leeching into the surrounding soil.

For beds that are 20 inches deep or less you should fill them completely with a premium topsoil blend which meets British Standards 3882:2007. If they go much deeper you can add some other natural material, like stones or lower grade, sandy soil, to assist with drainage.

Maintaining beds

You will need to replenish beds with soil or compost ahead of each growing season, to ensure it has sufficient nutrition to support new growth.

To remake a raised bed, first clear it of all grass, weeds, stones and other unwanted materials then turn over the top layer of existing soil to allow oxygen to enter. You can also poke through holes with a fork to break up the earth further down. Add the new topsoil to a depth of at least two to three inches and stir it up with the existing earth so the new soil is evenly distributed and ready to welcome new plants.

Refresh allotment patches

The typical allotment will need refreshment ahead of each new growing season. As with beds, you need to kickstart the process by clearing each patch of grass, weeds and larger stones and possibly adding a thick layer of compost or mulch if the ground has become very dry and depleted.

A golden rule of allotments is never to grow the same variety of plant in the same patch for two years running. You should ideally have a three year cycle whereby different families of vegetable and fruit are rotated around different patches to limit the chance of serious soil depletion, plant disease or insect infestations.

Premium topsoil should be added as a top layer to a depth of at least two to three inches for the optimum growth of new plants once the growing season gets underway. Then all you need to do is add water and sun then watch and enjoy as they grow to fruition!

Lay a Green Roof

Green roofs are a great way to regreen spaces, especially in urban environments where land is hard to come by. They not only offer great habitats for wildlife, but they provide insulation and will help prevent roof gutters from overflowing.

If greening the roof of your house is too tall an order, why not start off with the roof of your garage or garden shed and do that little bit more to help the environment?

They can be created on either flat or pitched roofs, with an optimum slope of up to 10°. For a slope above 20° you will need a frame to prevent it from slipping.

To build a green roof you should first ensure the building is in good order, waterproofed and able to take extra weight on the roof. A simple green roof will weigh 60-160kg per square metre and will get heavier in wet weather or when it snows. If in doubt about the weigh, take advice from a professional!

To ensure a roof area is waterproof, cover the area to be ‘greened’ with a heavy-duty rubber liner that will prevent water or roots penetrating the underlying roof material. Then add a protective plant fleece on top of the rubber lining. A flat roof can also take a 1cm layer of graven over the plant protection fleece to help with drainage.

The frame should be created from lightweight metal or rot-proof wood that will keep the soil and plants in place. It will need to be the same depth as the soil you’ll be putting on there and should be a minimum of 10cm. Secure the frame by nailing corners together or by using ‘L’ brackets. Add holes to the side of the frame nearest the ground to permit water drainage or leave a 1 cm gap between roof and frame so water can escape from the bottom.

The growing medium should be at least 10cm deep and might consist of 6cm of soil on top of 2cm of pre-vegetated mats. Wildflowers, sedum plants and herbs don’t have deep roots and should grow well in this type of environment. If you aren’t using pre-vegetated mats you can plant your seeds directly into 10cm of soil.

Not all Soils are created equal

A good topsoil should be free of undesirable features like roots, white fleshy weed roots (especially the dreaded Japanese knotweed), stones or even fragments of glass, plastic or brick. If you aren’t sure where it comes from ask your supplier and avoid anything that might contain recycled skip waste.

For environmental reasons you should also ensure any soil you buy is peat free. The Real Soil Company’s 100% natural, peat-free, organic and veganic SuperSoil has been created to help plants get off to the best possible start, without causing environmental damage. This nutrient dense, organic SuperSoil is composed entirely of peat-free enriched soil with the high phosphorous content essential for luxuriant foliage and vividly coloured flowers.

By contrast, a typical bag of topsoil from the garden centre or DIY store can have a high sand content and include wood fibre, peat, plastic and even glass from green waste sources. Not what you want in your flower pots or garden beds.