What’s the Difference Between Topsoil and Subsoil?

Topsoil vs Subsoil

Whether you’re sprucing up your garden on a weekend or diving into your first gardening project that needs that extra bit of research, understanding the soil type you’re working with is crucial. Whilst most people will think that garden soil is just a bit of dirt, it’s so much more than that – using the wrong type of soil can impact plant growth, lead to waterlogging and a lack of nutrients in your flower beds.

In this gardener’s guide, we’ll explore the difference between topsoil and subsoil as knowing how these layers work will not only boost your gardening knowledge, but also make your landscaping project that little bit easier!

What is Topsoil?

Topsoil is the upper layer of soil (typically 5 – 10 inches or 10 to 25cm deep) that contains most of the ground’s nutrients and fertility. Formed over a long period of time, topsoil is dark in colour, rich in essential nutrients and organic matter that most plants, vegetables and turf need to thrive, including nitrogen, phosphorus, potassium, and magnesium. This makes topsoil incredibly fertile and perfect for growing everything from lush flowers to your favourite veggies.

What is Subsoil?

Lighter in colour and just beneath the topsoil, you’ll find the subsoil. Similar to topsoil, subsoil consists of a mix of small particles like sand, silt and clay, but it contains far less organic material. Subsoil serves as an anchor within the earth, offering important drainage and acting as a foundation for the roots of trees and shrubs.to grow. Therefore, it’s important for subsoil to have the right balance of materials to allow water to flow effectively.

Key Differences Between Topsoil and Subsoil

Understanding the differences between these two soil types can make a big difference in your garden, so we’ve made an easy list for you to understand!

Nutrient Content

Topsoil is by far the better choice when it comes to nutrients. It’s where your plants get most of their food, so it’s important to have a high-quality topsoil! Subsoil, however, plays a supportive role, lacking in nutrients but crucial for structural purposes and allowing for proper drainage.

Texture and Composition

Topsoil is darker and looser, allowing roots to spread out easily and water to drain efficiently. Subsoil is lighter and denser, which helps prevent the soil above it from becoming waterlogged – ideally, a blend of premium topsoil and a multi-purpose subsoil is best!

Colour Variations

You’ll notice that topsoil is generally darker in colour because it’s rich in organic materials, whereas subsoil tends to be lighter, with variations depending on the local geology and soil structure.

Role in Plant Growth

While your plants live and feed in the topsoil, they rely on the subsoil for foundational support, making both layers absolutely necessary for a range of gardening projects such as a vegetable patch, laying new turf or filling in slopes!

Microorganisms and Life

Topsoil is more conducive to supporting living insects because it is directly exposed to the atmosphere and consists of small, loose particles. This structure allows creatures like earthworms, centipedes, millipedes, and other insects to thrive and make their homes in the topsoil. Subsoil tends to be more compact than topsoil, since it does not hold any air in the soil, therefore, any living insect cannot typically survive in this layer.

To Summarise…

As a new gardener, recognising the importance of both topsoil and subsoil will set your garden up for the long run. These soil layers work together in your garden’s ecosystem, each playing a critical role that supports lush, vibrant plant growth. By nurturing both, you’ll ensure that your garden not only looks beautiful but is also sustainable and healthy!

If you’re looking to improve your garden or thinking about starting a new project, Alsoils+ can provide the topsoil and subsoil you need. Working with both domestic and trade customers for the past 35 years, you can be sure we will deliver a high-quality service!

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About the Author

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The Alsoils Team

For more than three decades, Alsoils has been a trusted name in delivering superior soil, compost products and offering landscaping services. Based in Hampshire, Alsoils caters to a diverse clientele, including both homeowners and businesses. Our team are experts in all things gardening, so you can be sure you get the very best advice for topsoil, compost, manure and so much more!

Based on 14 reviews
Mark Belshaw
Mark Belshaw
Ordered 2 bulk bags of manure on Wednesday, late afternoon and all was delivered by Friday lunch time. Great quality product and excellent delivery turnaround.
Charles Smith
Charles Smith
Excellent, from order to delivery. 10 tonnes of loose load top soil delivered within a few days. Best price and the 10mm screened soil is great quality. Thank you
Lesley Barry
Lesley Barry
Excellent product ordered 4 bags of top soil the driver was so accommodating as we have a very long driveway. The customer sevice was excellent. Thank you.
David Robberts
David Robberts
Excellent product at a sensible price from a local supplier. Staff are friendly and willing to help: I asked if just one bag of topsoil could be delivered quickly and it arrived next day! Great service.
Mark Hibberd
Mark Hibberd
Smooth execution of the transaction and delivery. Very helpful phone call and conversation. Ordered three bags of Border Blend topsoil. Paid by Paypal. They delivered, on the specified date, carefully, exactly where I wanted the bags placed. All in all, a very pleasing purchase. The topsoil was excellent and had been very carefully prepared. No lumps. Would definitely recommend and I will use again. Everyone I spoke to was nice and helpful.
David Stamp
David Stamp
Ordered topsoil on Tuesday came by Friday at the exact time quoted. Was WAY cheaper than anywhere else (by about £15 per bag) and was dropped off via a crane on back of the lorry, not by pallet which most of the other places use. Soil was fine and dry. Brilliant !