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What’s the Difference Between Compost and Topsoil

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Are you a budding gardener looking to take your soil game to the next level? Or are you an experienced green thumb who is just looking for a deeper understanding to improve a healthy garden?

Understanding the difference between compost and topsoil is important to nurturing healthy plants and promoting robust growth. Let’s literally dig into the definitions of compost and topsoil, explore the unique benefits they bring to the table, and provide practical insights on how to integrate them into your own garden soil or vegetable garden.

By the end, you’ll be equipped with the knowledge to make informed decisions that will yield flourishing results in your garden (or even your lawn or flower beds). So grab your gardening gloves and let’s dive into the world of compost and topsoil!

What is Compost?

Let’s start at the top with what exactly is compost? You can buy it by the bag at local garden centers or make it at home, but what exactly makes it compost?

Compost is a nutrient-rich, organic material that is created by decomposing various organic materials such as food waste, yard debris (think grass clippings), and manure. It is often referred to as “black gold” due to its ability to improve soil structure, enhance moisture retention, and provide essential nutrients for plant growth.

So while some soil may be in compost, it’s not a material that you want to necessarily fill your raised bed with, but it’s still important, and it’s great use for all of your kitchen food scraps. Here are some helpful articles if you’re looking to get started composting at home:

three wooden bin compost system on green lawn

What is Topsoil?

Topsoil is literally the top layer of soil, typically the top 2-8 inches, where most of the nutrients and organic matter are concentrated. It is crucial for plant growth as it provides a stable medium for root development and nutrient uptake. 

Top soil is usually rich in essential minerals like nitrogen, phosphorus, and potassium, which are necessary for healthy plant growth. (These are also the 3 numbers you see on any fertilizer bag N-P-K, and knowing about your soil will help you choose the best fertilizer for your needs.) 

Understanding the composition and function of topsoil is essential for successful gardening and landscaping projects. See several of my full posts on soil and it’s importance:

How to Improve Garden Soil

What is soil?

Soil Structure and Function

When it comes to the soil in your backyard, raised bed, or row garden, structure and function are key factors in determining its overall health and ability to support plant life. The way soil is composed, how it retains water and nutrients, and its texture all impact its ability to nourish plants and promote growth. 

Understanding the structure and function of topsoil and compost is crucial for gardeners and landscapers looking to create a thriving environment for their plants. In short, I like to think of top soil as the structure and stability my plants needs for their healthy growth, and compost is an amendment I can add to soil to improve it and as a way to feed the plants growing.

Benefits of Compost

There are so many benefits to both using and/or making your own organic compost. Let’s break them down and hopefully encourage you to start using a layer of compost in your gardens, flower beds, and more! Adding compost to soil offers several benefits:

  • Improved Soil Structure: Compost helps to improve soil structure by enhancing its texture and porosity. It increases the soil’s ability to retain moisture, nutrients, and air, which are crucial for plant growth. This improved soil structure promotes better root development and overall plant health.
  • Nutrient-Rich Soil: Compost is a valuable source of organic matter and nutrients such as nitrogen, phosphorus, and potassium. As it decomposes, it releases these nutrients into the soil, providing a natural and balanced fertilizer for plants. This nutrient-rich soil supports healthy plant growth and can reduce the need for synthetic fertilizers, acting as a natural fertilizer.
  • Enhanced Microbial Activity: Compost contains a diverse community of beneficial microorganisms, including bacteria, fungi, and other soil organisms. These microbes play vital roles in nutrient cycling, disease suppression, and improving soil fertility. Adding compost to the soil fosters a thriving microbial ecosystem, which contributes to the overall health and productivity of the soil and plants.

These benefits of compost make it a valuable addition to any gardening or landscaping project, helping to create a fertile and thriving environment for plants to flourish. Next, we will explore the benefits of topsoil in further enhancing soil health and supporting plant growth.

Benefits of Topsoil

You naturally have topsoil in your yard and row garden, and you can buy it in bags at the hardware store or garden center, but do know that it is not the same as potting soil. Like compost, top plays a crucial role in creating a healthy and fertile environment for plants to thrive. It serves as the very topmost layer of soil, rich in nutrients and organic matter, essential for supporting plant growth. 

But if you already have topsoil in your yard in the existing soil, then when would you benefit from more of it? Well, not everyone has good quality topsoil in their current soil, and a home gardener may need to amend or add to what they already have. There are also issues with sandy soil, clay soil, or low spots that may benefit from more top soil. I know our dog loves to dig holes in our front yard, and I’ve used many a bag of topsoil to try and fill them. Sheesh. But see below for some practical applications for top soil and the best way to use this resource in your yard or garden. 

Practical Applications in Gardening

Both compost and topsoil have very practical applications in the garden. Plants need healthy soil in order to grow and thrive and since both topsoil and compost serve different purposes, you can use them both to create a perfect home for your garden plants. 

Good compost is incredibly versatile and can be used in various ways in the garden:

  • Soil Amendment: Mixing compost into garden soil improves its structure, texture, and fertility. It adds organic matter, nutrients, and beneficial microorganisms, creating a healthy environment for plant roots to thrive.
  • Mulching: Applying compost as mulch around plants helps conserve soil moisture, suppress weeds, regulate soil temperature, and provide a slow release of nutrients as it decomposes. It also enhances the visual appeal of garden beds.
  • Topdressing: Sprinkling compost on the soil surface around established plants provides a nutrient boost and helps replenish soil organic matter. This is particularly beneficial for perennial plants and shrubs.
  • Seed Starting: Mixing fine compost with potting soil or using it as a seed starting medium provides young seedlings with essential nutrients and promotes healthy growth.
  • Compost Tea: Brewing compost tea by steeping compost in water creates a nutrient-rich liquid fertilizer that can be applied to plants as a foliar spray or soil drench. It enhances nutrient uptake and boosts plant growth.
  • Compost Pile Activator: Layering fresh organic materials with compost helps accelerate the decomposition process in compost piles or bins, resulting in faster production of mature compost.
  • Container Gardening: Adding compost to container mixes improves water retention, drainage, and nutrient availability, creating optimal growing conditions for potted plants.
  • Companion Planting: Some plants benefit from the addition of compost as a side dressing or when planted nearby. Compost can help attract beneficial insects, repel pests, and enhance the overall health of companion plants.

A garden or yard may need additional topsoil for several reasons:

  • Poor Soil Quality: If the existing soil is poor in nutrients, organic matter, or has an unfavorable texture (e.g., sandy or clayey), adding topsoil can improve its quality and fertility. This is essential for promoting healthy plant growth.
  • Compacted Soil: Soil compaction can occur due to foot traffic, heavy machinery, or natural settling over time. Compacted soil restricts root growth and hampers water infiltration and air circulation. Adding topsoil can help loosen compacted soil and improve its structure. Though there are also other ways to amend compacted soil. 
  • Leveling and Grading: In some cases, adding topsoil is necessary to achieve a level surface or to correct grading issues that can lead to poor drainage or water pooling.
  • Planting Beds and Lawns: When creating new planting beds or establishing a new lawn, adding topsoil is often necessary to provide a suitable growing medium for plants, or to build up low beds. 
  • Raised Beds: For raised beds, additional topsoil may be needed to create the raised area and provide adequate depth for plant roots, though I recommend a good raised bed mix for most of the fill of a raised bed. See my full post on How to Fill a Raised Bed Cheaply

In summary, adding topsoil can help improve soil quality, promote healthy plant growth, control erosion, and address various landscaping needs.

Overall, compost and topsoil are valuable resources in the garden, providing numerous benefits for soil health, plant growth, and environmental sustainability. I’d love to know if you’ve used compost and or topsoil in your outdoor space, and if you noticed a difference in the quality of your soil overall. Feel free to comment below with your experiences!

Judy

Tuesday 26th of March 2024

Was interesting to read about the difference between compost and Topsoil. I’be always wondered this.