How Much Topsoil do I Need?
Not every garden is blessed with great soil. Some have soil that drains poorly while others are filled with rocks and lack much nutrients, with a wide array of problems causing soil quality to be less than ideal for growing plants in the garden. Thankfully, there are ways that you can improve soil quality!
Adding new topsoil is a great way to enrich and greatly improve the quality of existing soil in your garden. The process is straight-forward – you get new soil and add it to the top of your current soil, giving it an added boost of nutrients to create better growing conditions.
However, one of the big challenges of using topsoil is working out how much you need to use, as the amount required varies depending on what you plan on growing and the site where it’s going.
Recommended Topsoil Depths
The recommended topsoil depth varies from each project – you won’t need the same amount of soil for planting new lawn seed as you would adding new soil to an existing flower bed!
A few factors influence your soil requirements, including its location in your garden, what you plan on growing there, and the quality of any existing soil.
For example, new build properties tend to have dreadful soil due to the extensive construction work that was only recently finished. Soil here tends to be very shallow and lacking any nutrients, meaning you will need to add quite a lot of topsoil to improve the growing conditions.
Other projects won’t require as much topsoil. For instance, if your garden is well established and you have good quality soil, only a small amount is recommended to give it an added boost without overdoing it.
Sometimes you may just want to level out an area in the garden without caring about the soil quality. In this case, you’d only need the exact depth to reach the desired level without worrying too much about the type of soil you’re adding.
As you can see, the topsoil requirements tend to differ for each garden!
Here are some recommended topsoil depths for general garden projects:
Whether you are planting a completely new lawn or reseeding to cover up patchy areas, using some topsoil greatly improves growing conditions for new grass seeds, providing a consistent source of nutrients over the long-term.
Topdressing a lawn won’t only make grass grow back quicker, it improves the overall quality of the grass, resulting in fuller and greener growth throughout your lawn. You can also add topsoil to address various issues like drought and water logging, so it’s safe to say that topsoil is highly beneficial for a lawn!
Whether using topsoil for seed or turf the recommended depth is between 100-150mm. As mentioned, the current soil quality will impact how much you need, so if your soil is good quality then you won’t need to go as deep with your topsoil.
Given the added nutrients it gives your existing soil, it’s a great idea to add topsoil anywhere you plan on growing vegetables. The depth of topsoil needed depends on what you’re growing, with certain vegetables preferring shallower growing conditions while others need lots of depth.
For example, leafy greens like lettuce grow in shallow soil so you would want to add less topsoil, the same can be said for the broccoli, onion, courgette etc. The same can be said for herbs, with most being shallow rooted plants. In these cases, around 100mm of topsoil may work, depending on the current soil condition.
Other vegetables prefer deeper soil for growing, so if you plan on growing things like potatoes, peppers, parsnips, and tomatoes then more topsoil is recommended to accommodate for the deeper roots. In these examples, anywhere from 300 to 400mm of topsoil may be needed.
Related: What to grow in a greenhouse
If you aren’t planting fruits and vegetables or working on the lawn, then a good average depth for your top spoil is between 150 and 200mm. This should be ideal for most general planting, including flowers.
How to Calculate Topsoil Requirements
You need to know the measurements of the area you are planting in to work out how much topsoil is required. So, measure the width and length of the area in metres, then multiply this figure by the depth recommendations suggested above to get the volume of topsoil in cubic metres.
For example, if you are working on a lawn measuring 10m x 20m and need around 150mm of topsoil, the calculation is 10 x 20 x 0.15 = 30m3