Horticulture Magazine

Peat-Based Compost

compost being harvested from peatland bog

What Is Peat-Based Compost?

Peat based compost, as the name suggests, is a potting media or mix which includes a certain proportion of peat in its composition. Peat has traditionally been used by many horticultural experts and home growers to provide optimum conditions for their plants in pots, and to amend the soil in their gardens.

However, in recent years, there has been a shift away from peat for environmental reasons. Many compost or potting mix manufacturers have moved away from peat altogether, or reduced the amount of peat included in their recipe. Sustainable, eco-friendly gardeners have tried to move away from these options to ones that are peat-free, and have less impact on the environment.

What Are Its Benefits?

Peat has traditionally been used in growing media and soil amending composts because it is excellent for growing plants. Peat retains plenty of water and provides nutrients, while also providing a good texture that helps in maintaining aeration and avoiding compaction. Trying to recreate the qualities of peat with other materials has, historically, posed something of a challenge.

But research and development of new commercial products means that there are now alternatives, which provide the same benefits as peat, without posing the same environmental threat. The horticultural industry in the UK is still heavily dependent on peat as a resource – but things are beginning to change, with the proliferation of higher quality peat-free options. Now, there are many peat free alternatives that are just as good as peat based options.

One benefit of peat based composts that does remain is that they are usually cheaper than peat-free alternatives. This means that they can be particularly tempting for those gardening on a budget. One thing to remember, however, is that you can also keep down costs by making your own growing media. And/or by using other materials to fill raised beds (no dig gardening lasagna beds) so only a smaller amount of compost is required to top new growing areas.

How To Use Peat-Based Compost

A peat based compost, depending on its composition, can be used to grow a huge range of different plants. There are peat based composts that can be used for starting seeds, growing plants in pots, and for spreading around plants to build and improve the soil in your growing areas.

As mentioned above, peat is not a sustainable or eco-friendly choice. We’ll explain why in a little more detail below. So organic gardeners should always try to avoid using a peat based compost whenever possible.

Where it is preferable to use peat, and a good peat-free option cannot provide the same results (which is increasingly rare) gardeners should try to to choose a lower peat option.

Another potential option is to choose a compost that has peat sourced more sustainably – dredged from rivers and by dams where it has been naturally washed by rain, rather than choosing peat that has been dug up from its natural ecosystem.

What Plants Is Peat-Based Compost Good For?

There is no denying that peat based compost is great for growing a wide range of plants. There are peat based media that can be used for growing most plants from seed to maturity. (But also usually peat-free composts that can do just as good a job.) When starting seeds, multi-purpose composts can sometimes be used. But a specialist seed starting mix might yield better results. For ericaceous plants, a specialist acidic mix should be used.

What Are Its Disadvantages?

The main disadvantage of peat based composts is the harm they do environmentally speaking.

Peat comes from lowland peat bogs. When we use it on a large scale in the horticultural industry, we are damaging these precious wetland environments. The problem is that although peat is a natural resource – we are using it up far faster than it can be replenished. And we need those peat ecosystems to remain for a number of reasons.

Firstly, and importantly, peat bogs are a crucial carbon sink. Peat wetlands are the most important ecosystems for carbon sequestration on our planet. Peat wetlands store more carbon than all other vegetation types, including the world’s forests. Peat covers just 3% of the world’s land area, but stores 1/3 of the Earth’s soil carbon. When peat is removed and peat ecosystems are degraded or destroyed, these ecosystems can no longer play their role in maintaining the world’s carbon cycle. We need to sequester more carbon, and lock it up in peat bogs and other carbon sinks in order to tackle the massive climate crisis we face.

Wetlands are also very important in the water cycle. When we destroy peat bogs, we risk disrupting the flows of water through our environment. This can have a profound effect on our lives. Currently, more than 28 million people in the UK rely on drinking water from sources that rely on peat ecosystems. Globally, peatlands filter water. They provide nearly 4% of all potable water stored in reservoirs.

What is more, when peat ecosystems are degraded, water can also pass across a landscape more quickly. When we take peat away, or disrupt natural systems, this can cause major flooding issues for communities at lower elevations.

And it is not just people affected by peat removal. Many species of flora and fauna also rely on precious peat habitats. Wetlands are the most biodiverse of all nature’s ecosystems. When we disrupt and disturb them, we are contributing to habitat loss and biodiversity losses.

These are just some of the main reasons why we should be leaving peat in the ground, not stealing it to use in our gardens.

Frequently Asked Questions

Is Peat Based Compost Acidic?

Peat itself has a low pH and is acidic. Sphagnum moss peat typically has a lower pH than sedge peat which is more variable – its pH can depend on the water of the area from which it was collected.

However, when you purchase peat in a potting mix of commercial compost, it will typically have been formulated to provide a balanced PH, with other ingredients added to counteract the acidifying nature of the peat. The exception to this, of course, is ericaceous compost or potting mix, which will have been formulated to provide acidic growing conditions for acid-loving plants.

One thing to note is that peat will not acidify soil in your garden long term, as pH will usually depend on the water and natural rainfall, as well as the natural soil in your area. If you want to acidify soil, this is something that you can only do with repeated application of acidic organic matter.

Usually, it is best to choose plants suited to the soil pH where you live, rather than trying to grow acid loving plants in an alkaline environment. Where you have alkaline conditions but want to grow acid loving plants, grow these in containers filled with ericaceous compost. But remember that you will have to refresh it regularly to maintain acidity levels.

What Is Peat Moss-Based Soil?

A natural peat soil is rare in UK gardens. However, it can be found in some areas. Peat soils are mainly made up of organic matter, with fewer mineral particles. They are usually very fertile and hold a lot of moisture. Usually, the pH in such areas is low. Gardeners may have far fewer choices about which plants they can grow if they have this type of soil, rather than a more typical clay, silt, sand, chalk or loam in their gardens.

When people talk about peat moss based soil, they are more likely to be talking about a peat based potting mix or growing medium, rather than a natural garden soil type. These (and peat free alternatives) are used in pots and containers, or to add nutrients and improve the structure of soil of a different type.

Why Should Gardeners Use Less Peat-Based Compost?

As mentioned above, removing peat from its natural ecosystem is extremely environmentally damaging. It hastens global warming by reducing the size and efficacy of carbon sinks that cannot grow back quickly. It causes disruptions to fresh water supplies and can cause flooding issues when wetlands are degraded. And using peat hastens biodiversity losses and is terrible for wildlife.

The other thing to remember is that there are peat-free options available. And these can now be genuinely just as good as the traditional peat based options. Purchase more sustainable potting soils or soil amenders. Or better yet, consider making your own and creating closed loop systems to return nutrients to the soil in your garden.

Can You Mix Loam-Based and Peat-Based?

Peat based composts (and peat-free options) sometimes come with ‘added John Innes’. Adding this loam based potting medium to a soil-less mix is sometimes done to improve the buffering within the product, boost trace element content, and improve weight.

However, when loam-based media have been added to a peat-based or peat-free compost, this has been done very carefully, to a specific formulation. Mixing media yourself at home is not recommended. In part, this is because loam-based media have very fine particles that can fill or block air spaces in the medium and cause aeration or drainage issues.

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