Are you trying to decide which type of compost is best for your gardening needs?
With so many options available, it can be overwhelming to determine the right choice.
In this article, we’ll guide you through the various types of compost and their uses. We’ll also explore the factors to consider when selecting a compost, such as its intended purpose and ethical considerations, and whether it is worth making yourself.
By the end, you’ll also have a better understanding of whether it’s more convenient to purchase the particular compost you need or make it yourself.
At a glance (click for larger image)
Just in case you’re in a hurry, I’ve summarised the main types of compost in a mini-infographic.
For more detail (and more types of compost) read on.
What is seed compost?
Seed compost is also known as potting compost.
It is lower in nutrients than standard multi-purpose compost, providing enough nutrition for young plants to grow without too much nitrogen that can damage young roots.
It is also light and airy, carefully balancing the ability to drain water and provide oxygen while holding sufficient moisture for early growth of young plants. Typically seed compost combines standard compost with other ingredients such as coir or perlite.
Watch out for…!
While seed compost is generally low in nutrients, it does need some. Tests by Which! have found that pure coir composts which are not enriched with nutrients perform poorly. Seeds germinate in the composts, but fail to grow on afterwards. In contrast, the top performing compost in UK tests is Fertile Fibre Seed Compost.
Do you need seed compost for seeds?
Sellers of seed compost will obviously say you need seed compost. While seed compost is undoubtedly the best option for seedlings, it’s not essential.
Firstly, plants in the wild successfully survive and thrive without being able to choose the exact compost they need. It’s true that most plants have gone many years (sometimes centuries!) of selection – and they have been selected for other properties than their ability to germinate in rough ground. Still, many seeds will still be able to germinate in more than just seed compost.
Secondly, many seeds will grow in the ground. They will germinate better in compost trays, but that’s at least partly because of a protected environment.
Thirdly, I have germinated many seeds in multi-purpose compost (and some in garden soil). It’s not ideal, and I have had failures – but plenty of successes too.
What seed compost will do is give you the best germination rates and reduce failures.
Can you make your own seed compost?
You can make your own seed compost, but it does involve a bit more than making general purpose compost for enriching your soil. You want fine compost that has had plenty of time to mature. You then want to sieve the compost to remove any woody bits and big lumps.
You can then mix the compost with other ingredients to reduce the nutrient value. Mr Fothergills recommends mixing two parts of compost, two parts of coir or coconut fibre and part of perlite, which makes the compost lighter and airier.
An alternative is to mix the compost with sand. It’s best to use sand without salt rather than from the beach. The sand can be used to either replace the perlite or to replace both the perlite and the coir. This will make a heavier mix than using perlite and coir.
Some blogs recommend sterilising seed compost. This was popular in years past, when soil was sterilised in ovens before using.
I’m sceptical about this. It’s possible that it might be advantageous for some very sensitive plants, but it also means destroying all the beneficial microorganisms available in the compost.
In the past, when sterilising was popular, we thought that gardening was simply a matter of providing nutrients to plants. We now know that this is not the case. Bacteria and fungi interact with plants, helping them to grow. It’s also certain that bacteria will quickly re-inoculate the compost – and far from certain that the new bacteria will be the helpful kind.
Personally, despite gardening since I was a child, I have never sterilised compost, and neither do any of my gardening friends.
Multi-purpose compost is designed for more general use in the garden. It can be used for:
- potting on seedlings and plants
- adding fertility to existing pots
- for hanging baskets
- enriching soil
Store bought compost is finer than standard home made compost, and is sometimes enriched with plant food.
Some composts give you a guide to how long the nutrients in this compost will last for. This should be treated very roughly, as it will depend on the plants you are using, growing conditions and so on.
Can you make your own multi-purpose compost?
If you have any sort of garden, I highly recommend you make at least some of your own compost.
Making compost is really not that difficult, and doesn’t take a lot more time than bagging up garden waste and leaving it out for the rubbish collection.
What’s more, if you want to use compost to condition your soil, it can be expensive to buy the quantities needed. However, it is difficult to achieve the same results as store bought compost, which comes with an ideal PH level, excellent moisture retention and is often enriched with nutrients.
One option is to mix and match home based compost with store bought compost. I often use home made compost for mulching, topping up raised beds and in the bottom of larger pots, while using multi-purpose compost for young plants and for topping off larger pots and raised beds in polytunnels.
Learn how to make compost with our Home Composting Guide
Peat Based Compost
Peat based compost contains a large amount of peat. Peat is a naturally occurring material which is made up of partially decomposed organic material which has built up under water-logged, oxygen deprived conditions.
Peat has many good properties. It retains moisture well, has the perfect texture for plants and contains good nutrients. Put simply, plants grow well in it.
The problem is peat lands take hundreds of years to form, and are a scarce resource. They lock up large amounts of carbon until they are dug up. The sheer amount is incredible – peat covers just 3% of the world’s surface, but stores more than 600 gigatonnes of carbon. That’s more than the carbon stored in all the world’s forest. They are also important for biodiversity.
From 2024, at least in the UK, amateur gardeners won’t have any choice, as peat compost will be banned.
As the name suggests, peat-free compost is any compost that does not contain peat. Your home-made compost is peat free, and you can also buy peat-free compost in the stores.
Peat free compost combines a mixture of organic material with inorganic materials such as sharp sand and perlite.
I remember as a child my father trying to use peat-free compost, and complaining the results were not as good. However, there have been major advances in composting technology since, and many modern brands provide good alternatives to peat-based compost.
Loam is soil that contains a balanced mixture of three types of soil; clay, sand and soil. Loam based compost is traditionally based on loam soil, often combined with peat and organic materials. However, some modern composts may use other ingredients.
Loam based compost is typically used to improve the structure, drainage and fertility of a soil. It has a neutral PH level, which can make it a better option than multi-purpose compost for plants that prefer a slightly alkaline soil.
Can you make loam based compost?
Yes. You can make loam based compost by first combining equal parts of sand, silt and soil. You then mix in organic material such as leaves and grass clippings.
Add water if needed – the finished mix should be damp but not soggy.
Leave for several months until the final mix is fully decomposed and looks and smells like dark, crumbly soil.
You’ll also see compost marketed as organic. This is a misnomer, as all compost is made from organic material. Legally, the term organic can be applied to foods, but not to compost.
Some composts are marked as chemical free – but again, all compost contains chemicals! It’s far more important to buy compost which is pesticide and toxin free.
For a complete guide, as well as the best compost options for the organic and ethical gardener, see Organic compost: Black Gold or Commercial Hype?
Ericaceous Compost is named after the type of plants that grow well in it. Examples include Rhododendrons, Azaleas, Heathers and Blueberries. These plants prefer soil with a higher acidity, and do not grow well in alkaline soils. Ericaceous Compost has a higher acidity level than regular compost which makes it well suited to these plants.
It is possible to make Ericaceous Compost at home, but it is hard to do so without using some peat. Fortunately, according to the RHS, commercial peat-free Ericaceous Compost is improving and is becoming a viable alternative to peat-based Ericaceous Compost.
Cacti and Succulent plant compost
Cacti and succulent plant compost is a special type of compost that aims to replicate desert soil – well draining and low in nutrients. (Do note that all cacti are succulents, but not all succulents are cacti.)
Typically succulent compost contains soil, sand and/or grit as well as soil. It may also contain perlite and peat and/or specific plant nutrients suited for succulents. The mixes aim to achieve specific levels of PH balance, nutrition and drainage.
Can you make cacti and succulent plant compost?
Yes, you can, although you’ll find some disagreement on the perfect mix! Simplify Gardening has an excellent article on the different materials you can use, as well as the mixes you can use for different types of succulents.
Bark Chip/Wood Chippings Compost
As the name suggests, bark chip or wood chippings compost is simply compost made from bark or wood, sometimes combined with other organic material. Wood compost is high in carbon, and lower in nitrogen than standard multi-purpose compost. It is also more alkaline, making it unsuitable for Ericaceous plants.
Wood compost is often used for mulching, where it improves soil structure, drainage and slowly releases nutrients into the soil. Wood chippings is a carbon rich compost, which will release its nutrients more slowly than nitrogen rich alternatives. This makes it suitable for long term soil improvement.
Wood compost may also benefit beneficial fungi in the garden more than composts made from green manure. Indeed, since I’ve started using wood shavings as a brown material in my compost heap, I’ve noticed some fantastic mushrooms growing in my polytunnel – including some edible ones which have made it onto our plates!
Do note you can also make your own leaf mold compost. It’s easy (although it does take a while), and it also has a high carbon ratio. Learn how to make it here!
Can you make your own bark chip compost?
Composting your own wood chippings is perfectly feasible, and wood chippings are often available for free or at a low price from wood yards and tree surgeons. If you build a large enough pile, it is perfectly feasible to generate heat too – in fact, wood chipping piles have even been used to heat a house.
The big factor to take into consideration is the quantity you need. If you need a lot, and can build a large pile (ideally at least a metre high and two metres wide) it’s more economical to create your own wood chip or bark compost. If you just need a few bags, you’ll be better off purchasing your own.
An alternative is to use wood chip paths between your vegetables. You want to keep the thickness quite thin, so the wood doesn’t leach too much nitrogen from your soil. The wood will initially help suppress weeds, and over time it will slowly rot into the soil, releasing carbon and nutrients.
Biochar compost may refer to compost which uses biochar in the composting process, or which combines biochar with other ingredients such as regular compost or coir.
Biochar itself is a substance created by burning organic material from forests and farms. The burning process, called pyrolysis, uses very little oxygen, which helps minimise carbon loss. The result is a material which looks like charcoal, but is a more stable and cleaner form of carbon. It also has a high cation exchange capacity, which means it is much better at holding onto nutrients than typical garden soil.
Although more research is needed into biochar, some studies have shown that the use of biochar compost can have major benefits for soil. For example, one study by Antonangeloa, Sun and Zhanga added biochar to the composting process. They found that after adding the finished compost to garden soil, soil health improved and crop yields improved by up to 300%. The same study found that biochar helped reduce the amount of toxic metals in soil.
Another trial was conducted in two vegetable gardens in Wales. In the trial, biochar was added to a low nutrient compost. Although less dramatic, the results were still positive, with an average 14.8% increase in yields.
It’s worth noting that biochar is nothing new – indigenous Amazonian farmers have combined biochar with organic material for centuries.
Can you make your own biochar/biochar compost?
Yes, biochar can be made both in metal drums and in trenches. It is a fairly involved process and unlikely to be as efficient as that made commercially. If you have the time and energy, it should be fun, but otherwise it’s probably easier to purchase.
However, you can also add biochar to your compost. As we saw in 16 Ways to Speed Up Compost, research suggests that adding as little as 3% can improve the speed of your composting process.
Sheep Wool Compost
Sheep’s wool compost uses sheep wool often combined with other materials such as bracken. The compost has excellent water retention and slow release nitrogen properties, making it a great alternative to peat. It is also likely that the low cost of sheep wool, which has plummeted over recent decades, has increased the viability of using the material.
Can you make sheep’s wool compost?
Yes, sheep’s wool can be combined with other composting materials to make your own compost. One experimental study suggests that a combination of 25% sheep’s wool with 50% grass clipping and 25% manure work best. The same study stated that it is essential to separate any compacted wool.
You can also compost sheep’s wool that is used in packaging. My own experiments have also shown that it helps to pull this wool apart when composting, as a failure to do can lead to clumps of uncomposted wool showing when turning compost. The amount of work involved, though, would deter me from composting a large amount of sheeps wool unless I had access to specialist equipment!
Used mushroom compost is used by many gardeners. It is usually made from straw, and may also be made from chicken manure. It also often contains peat. The compost is alkaline in nature, with chalk often used to increase alkalinity. Mushroom compost has a high organic content, and a reputation as an excellent compost. Some sources suggest it has a medium level of nutrients, possibly because it has already been used to grow mushrooms. It is often sterilised before being sold.
An analysis of fresh mushroom compost by Fidenzal et al in Pennsylvania found that the compost had a PH of 6.6 and a C:N (carbon to nitrogen ratio) of 13:1 – both of which are in the range of ideal garden compost. However, mushroom compost can vary depending on the materials used, and the RHS warns frequent use of mushroom compost may lead to chalk build up. Gardeners with alkaline soils would be particularly advised to use the compost sparingly. Occasional use is unlikely to do any harm to gardens
Charles Dowding Compost Comparison
No Dig guru Charles Dowding has run several planting trials on different types of compost, and ironically just as I was finishing off this post he came up with another one.
This trial compares the differences between soil, mushroom compost, wood compost (sieved and unsieved), green waste compost and Moorland gold. It’s a particularly interesting take as it looks at using compost for a longer period of time (with a second crop of leeks following potatoes).
Which compost brands are best?
If you decide to buy your own compost, you’ll want to know the best brand. However, it is hard to recommend brands, because results can vary from year to year.
In planting tests compost brands seem to perform differently from year to year, while lab analysis commissioned by companies such as Which! show that even respected brands may occasionally have some pesticides in them.
(I do recommend checking out the compost buying guides on Which!, although unfortunately there is a paywall.)
That said, it is worth avoiding some of the very cheapest brands, which can come filled with bits of plastic. If they don’t sift plastic from compost, it’s unlikely they take other measures to eliminate pesticides and ensure quality!
Here in the UK I have always had excellent results using John Innes compost, and I find this has a good balance between quality and price.
Dalefoot compost, which rather uniquely is made from sheep’s wool and bracken and is also recommended by Which!, would be my first option for smaller amounts of compost.. (Which!’s top choice, at least for seed compost, is Fertile Fibre. Although I haven’t tried this one yet, it has performed amazingly well in lab and growing tests.)
There are many different compost types. Given the length of this post, I’ve covered some of the most common types here, rather than every one. Let me know if this works for you – if you think it should be expanded with types such as worm compost, leaf mould compost, manure compost and more, just get in contact 😉
The Types of Compost mini infographics by CompostMagazine.com is licensed under a Creative Commons Attribution 4.0 International License. It can be re-used with attribution to this post.