Compost Vs Potting Soil: Which Is Best? | Polytunnel Gardening (2024)

One of the most confusing issues for new or inexperienced gardeners is whether they should use compost or potting soil. What’s the difference between potting soil and compost? Which type of compost or potting soil should I use? There are so many options to choose from for different jobs around the garden. This can sometimes seem rather confusing when you are new to growing your own. Compost vs potting soil: which is best?!

Don’t panic! To help you understand your options, and which one you need, we’ve put together this basic guide exploring compost vs potting soil to lead you in the right direction.

Compost vs Potting Soil: What’s The Difference?

The main difference of compost and potting soil is the amount of nutrients they contain. Depending on it’s creation, potting soil tends to have few nutrients. Potting soil is specifically designed to thrive in certain conditions, including good air exposure, drainage and water. Because of its composition and lack of nutrients, many gardeners use potting soil to help nurture plants they are growing in containers.

On the other hand, compost is packed full of nutrients that are able to enrich the soil and help boost the growth of plants, particularly those outdoors or in large pots. Plus, depending on its ingredients, compost is often more variable and able to boost plant growth with little maintenance.

Overall compost vs potting soil is a fairly even fight. Essentially, they both work to provide nutrients to plants, only in different conditions.

Can You Use Compost Instead of Potting Soil?

Yes, you can use compost instead of potting soil. Doing so will boost the growth of your plants and help them grow strong.

However, I’d strongly recommend mixing both. This way, your plants will receive the benefits of both compost and potting soil without losing out on nutrients, water retention and support.

How Can You Use Compost vs Potting Soil In Your Garden?

Whether you favour compost or potting soil, it is useful to take a look at the different ways that compost and potting media are used in a garden. They can be used:

• As a mulch on garden beds or borders, to amend and improve the soil and keep up fertility over time. (Traditionally, they were often dug in. But in a no dig garden, it is best to leave the soil as undisturbed as possible, keeping digging and tilling to a minimum.)
• To fill (or top off) raised beds. Building layers of organic material to compost in place, then potting beds with a thin layer of compost/ potting soil can be a good way to make new growing areas more cheaply. And to make use of natural materials at your disposal.
• For sowing seeds into in seed trays, flats or pots.
• To fill containers and planters in a container garden.

Types of Compost or Potting Soil

So, now you know the difference between compost vs potting soil, let’s take a look at the different types of compost and potting soil that you might use in your garden and where they might be used. We’ll take a look at:

• Homemade Compost
• Multi-Purpose Compost (Peat Based or Peat Free)
• Seed Starting Compost
• All-Purpose Potting Soil
• Organic Potting Soil
• Potting Media For Container Plants (Soil Based or Soil Free)
• D.I.Y Potting Soil

Types of Compost

Homemade Compost

A homemade compost can and should be a key feature of any organic garden. Setting up a composting system to process kitchen scraps, other compostable material from you home, and vegetative matter from your garden should be a top priority.

It is important to understand, however, that a homemade compost is not the same as a compost or potting medium that you can purchase online or from a garden centre or shop. A compost differs from a potting soil because a potting soil is a combination of different materials which has been carefully created to optimise growing conditions for plants.

Homemade compost is great for adding as a mulch on growing areas. And for enriching the soil in your garden. But if you want something to fill pots and containers, it should usually be combined with other materials for best results. (More on making your own potting medium can be found later on in this article.)

Multi-Purpose Compost (Peat Based or Peat Free)

If you are buying a compost for your garden, then it is important to understand the different options available. Multi-purpose or all-purpose composts are designed to make your life easier – since they are formulated to make them suitable for a wide range of garden jobs.

Multi-purpose composts can be used to amend the soil, as a mulch. They can be used for filling raised beds, planters or containers. And sometimes, they can even be suitable for seed starting.

It is important to understand, however, that not all multi-purpose composts are created equal. Some are far better quality than others. Often, even those which are purportedly for all the above uses will not necessarily give the best results.

Multi-purpose composts are formulated to provide suitable growing conditions for a wide range of different plants. But it is important to consider which plants you wish to grow. Since some will require different, specialist compost formulations. For example, if you wish to grow acid-loving plants, then a special ericaceous compost may be required. Other plants may need a specialist, more free-draining medium.

Peat Based or Peat Free

Multi-purpose composts can be broadly divided into two main categories – peat based and peat free. Peat based options contain peat – from peat bogs. But in an eco-friendly organic garden, peat based options should always be avoided. Using peat in our gardens does great ecological harm. It contributes to the destruction of precious peat bog ecosystems. Systems which we need for carbon sequestration, biodiversity, and for our water cycle. So if you want your gardening efforts to be as sustainable and eco-friendly as possible – always choose peat free options.

Rather than using peat, peat free formulations rely on other natural ingredients to provide suitable fertility and growing conditions. Peat free formulations may contain a proportion of green waste. They often also include coconut coir, or woody materials (well-rotted wood chip etc.). And may also contain ingredients like bracken, sheep’s wool etc..

Organic Composts

Another thing to think about when choosing a multi-purpose compost is whether the mix is organic, or contains other materials which may be harmful to the environment. Some mixes, for example, may contain things like synthetic fertilizers, which pose a risk to natural environments. These are obviously also to be avoided in a sustainable and eco-friendly organic garden.

Seed Starting Compost

A multi-purpose compost may be great for mature plants. But might not provide optimal conditions for seed starting. While you can create your own seed starting mix, you can also consider purchasing specific formulations designed for seed starting.

A mix for seed starting is typically a light, aerated and friable mix, with small particle size. It should be relatively free-draining, yet retain sufficient moisture. It does not need to be as rich in fertility as a mix in which plants will remain during their lifecycle. Or for composts which are to be used as mulch in your growing areas.

Types of Potting Soil

All-Purpose Potting Soil

All-purpose potting soil is the regular potting soil that suits indoor or outdoor plants that you’re growing in containers. Usually, all-purpose potting soil is made with a general mix of ingredients that aren’t aimed to help certain plant families, including soil, compost and perlite or sand. If you’re just starting out with potting soil and aren’t sure what to try, all-purpose potting soil shouldn’t let you down.

Organic Potting Soil

Organic potting soil is a natural alternative to all purpose potting soil, providing the same benefits without causing harm to the planet. Usually, organic potting soils are composed of plant and animal-based natural materials, such as food compost, animal manure and decayed plant matter. Organic potting soil is incredibly fertile since its natural blend of ingredients provides a higher level of minerals and nutrients than other potting soils[i].

Potting Media For Container Plants (Soil Based or Soil-Free)

Many formulations that you can buy are specifically designed for use in containers or pots. These mixes can provide suitable growing conditions for a wide range of container plants. Potting soil can be soil (loam) based, or soil free. Soil based potting soil (John Innes) contain sterilised loam and there are different formulations suitable for different plants which are well tried and tested for different applications. But soil free options are also available – often containing coir or other natural materials.

Make Your Own Potting Soil

You can also consider making your own potting soil/ compost for containers or garden plants. You can make a soil based mix, or a soil free formulation yourself at home.

One of the simplest options for filling pots is to take around 1/3 friable loam/ good quality garden soil, 1/3 homemade compost, and 1/3 leaf mould, and using this to fill your pots. I like this option since all three ingredients are ones which can ultimately, long term, be sourced/made at home, using ingredients from your own home and garden.

The problem with DIY soil based potting soils is that they can harbour fungi, and weed seeds which may pop up. If this is an issue, you can consider sterilising the soil/ loam in your oven. But this is not always necessary.

Soil free media can also be made at home, using well-rotted woody material, or ingredients like coconut coir. There are a number of different recipes which can be considered to meet the needs of a range of different plants that you may wish to grow.

Compost Vs Potting Soil: What Do You Think?

The answer to compost vs potting soil is completely up to you: they’re your plants, after all! Finding what works for you, your plants and your garden will be the most beneficial to the results you see. Try one or the other, or even a mix of both, and find what helps your garden.

Compost vs potting soil: what do you think? Any tips of your own? Let us know your thoughts below.

Sources

[i] https://www.backyardboss.net/organic-potting-soil-vs-non-organic-potting-soil/