Horticulture Magazine

Organic Compost

seedlings growing in compost

The term ‘organic’ can be a confusing one.

The term is sometimes used to describe anything of, relating to or derived from natural living things.

This is the definition we use when we talk, for example, about adding organic matter to the soil in our gardens.

What Is Organic Compost?

Organic composts are any composts (or potting mixes) that do not contain any synthetic fertilisers, and which contain ingredients grown organically.

And they may also be (though are not necessarily) free from peat, since though peat is a natural material, extracting it for garden use is hugely damaging to the environment. [source]

However, when it comes to buying compost, we are using the term ‘organic’ in a narrower sense.

An organic product is a product that is grown/made without the use of man-made fertilisers, pesticides, herbicides or other harmful chemicals.

Holistic organic production, however, also involves a systems approach that works towards environmentally, socially and economically responsible production.

Of course, the easiest and cheapest way to get your hands on some organic compost is to make your own in your garden.

Homemade compost is the most eco-friendly and sustainable choice of all. [source]

Since you make it yourself, you will know exactly what has gone into it, and will have ultimate control over the credentials (and quality) of the product.

However, there may sometimes be times when you cannot make enough, or cannot do so quickly enough. In which case, buying organic compost is the next best choice, environmentally speaking.

Buying organic compost that is free from harmful chemicals, and peat-free, is a far better choice than selecting other forms of compost, which will pose a threat to the environment.

Though it is important to work out whether you want a true compost, or are actually looking for an organic potting mix, as these are two different things.

What Is It Made Of?

Organic compost can be made up of a range of different materials.

If you are making your own organic compost then of course it will be made up of all the different ingredients that you added to your composting system.

It will contain both brown (carbon-rich) and green (nitrogen-rich) materials.

If you purchase an organic compost, it will usually be either a soil-improving compost comparable to a homemade compost, or a potting mix.

Which one you will choose will depend on how exactly you wish to use it in your garden.

Organic potting mix is usually a soil-free mix, which includes a proportion of composted waste, mixed in with a substrate of other peat-free materials.

Organic composts or potting mixes can be purchased which have a range of different ingredients and formulations.

Some, for example, are made from a mix of composted forest or garden cuttings –  or organic green waste such as composted bark fines, coconut husk, bracken, wool etc.

Of course, whichever ingredients go into the blend, these are organic in origin.

Though organic composts do not contain the synthetic fertilisers that are added to some other composts on the market, the blends have been carefully worked out to ensure good fertility and good plant growth and so results are now comparable with other non-organic options on the market.

How To Make Organic Compost

There are a number of ways to make your own organic compost at home.

You can compost in place in a no dig gardening system, or set up a simple cold composting heap or bin.

You can also speed up decomposition by aerating the mix (with a compost tumbler, for example), by enlisting the help of special worms (and setting up a vermicomposting system), by increasing temperatures (and making a hot composting system) or by using bokashi systems (and fermenting scraps prior to composting).

Of course, whichever composting method or methods you choose, it will only be organic (in the narrower sense) if you garden organically and none of the ingredients you add are contaminated with pesticides, synthetic fertilisers or other harmful substances.

If you want to create your own potting mix, you can do so by combining this sort of homemade organic compost with other ingredients.

You can make a soil-less or soil-free potting mix by combining homemade compost with a loam or garden soil, leaf mold, or other ingredients that will reduce density and create a more friable, aerated mix.

Organic Compost vs Potting Soil

An organic compost is used to add fertility to growing areas and improve the soil.

It is an essential ingredient in organic gardening.

Organic compost can be used as the top layer for new no dig garden beds, and spread as mulch around your plants.

An organic potting mix is formulated specifically for starting seeds, and growing on plants in pots.

It is also a medium designed to promote healthy growth for plants grown in containers.

Typically lower in nutrients, but with a better texture for water retention/ drainage and aeration, a potting mix will usually also require the addition of organic fertilisers throughout the growing season.

Frequently Asked Questions

Is All Compost Organic?

As mentioned above, ‘organic’ is a term that can be used in different ways.

If you are using the broader definition (of, or derived from living material) then most composts or potting soil mixes can be described as organic.

Peat based and peat-free composts which do not include synthetic fertilisers are made up of organic (or natural) material.

It is worth mentioning that organic means of or derived from living material, while natural can also include material that comes from nature, but which is not from plants or animals.

This might include the minerals in loam, perlite and vermiculite, for example.

But just because something is ‘organic’ in this broader sense, or ‘natural’ that does not necessarily mean that it is a sustainable or eco-friendly choice.

As mentioned above, an organic product is a product that is grown/made without the use of man-made fertilisers, pesticides, herbicides or other harmful chemicals.

But organic production also involves a systems approach that works towards environmentally, socially and economically responsible production.

This often rules out products that are natural, but finite, and can be environmentally costly in how they are extracted from the earth.

So in this narrower definition, most composts on the market are not truly organic, nor are they an environmentally-friendly choice.

This is why it is best, wherever possible, to make your own, or to purchase a certified organic option.

Where Can I Buy Truly Organic Compost?

Organic compost or organic potting soil is increasingly being offered as an option in garden centres and plant nurseries.

However, you may find it easier to find organic options online.

Here are a few great options:

One other recommended sustainable option, though not completely certified organic in origin is:

Melcourt Sylvagrow Sustainable Growing Medium (Endorsed by the RHS).

What Are Common Organic Materials Found In Compost?

Carbon-rich materials in an organic home-made compost often include:

  • Straw
  • Woody materials
  • Dried leaves
  • Untreated cardboard or paper.

Nitrogen-rich materials in homemade compost often include:

  • Green leafy material (from organically grown garden plants)
  • Glass clippings (only from untreated lawns)
  • Kitchen scraps (again, organic)

A bought organic compost/ potting soil can contain a wide range of ingredients, balanced to provide exactly what growing plants need –

Dalefoot composts are mostly made up of potash rich bracken. Herdwick sheep’s wool is also added for water retention and slow-release nitrogen. They are peat-free and contain no green waste.

Fertile Fibre composts contain certified organic coir.

Moorland Gold organic compost does contain peat. But that peat, and also leaf mould in the mix, are collected from lakes and dams where they have naturally been washed to by the rain. So choosing this option does not destroy peat bogs.

Why Does My Organic Compost Smell So Bad?

If you are making your own organic compost and it begins to smell bad, this is usually a sign that the heap has become anaerobic.

In other words, the waste is decomposing without sufficient oxygen.

In home composting, you are usually aiming for aerobic composting, which involves materials decomposing in an environment with sufficient oxygen.

The compost in a home system can become anaerobic for a number of reasons. Usually it is because:

  • The compost has become compacted, and has not been turned to increase aeration.
  • Your compost has become too wet, which has also decreased the air in the mixture.
  • You have added too much nitrogen rich material at once, without adding carbon rich material. Too many grass clippings, or too much kitchen waste, for example, can compact down and will reduce aeration. You should always make sure that you mix brown and green materials.

Occasionally, the smell may be due to the fact that there are not sufficient numbers of micro-organisms that are required for aerobic composting to take place.

You may also have added ingredients to a cold composting system that are not suitable for this method – such as meats, oils or fats and dairy products, for example.

Use a bokashi method to ferment these things before adding them to a typical home composting system.

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