Date: October 2, 2022

Types of compost

We make compost in lots of different ways, from lots of different materials. This short blog describes a bit about some of them.

Green waste compost:

This is what we make from the waste and debris from tidying up our gardens: hedge trimmings, grass cuttings, weeds etc. If we make it properly – balancing any wet squidgy grass with lots of brown materials, ensuring that the mix is neither too wet nor dry, dense nor loose – then it is easily done. We can either use the quicker but more labour-intensive hot composting method, or a slower cool composting method.

The resulting compost should be crumbly and spongy. It will greatly improve soil health, structure, and microbial population. It will facilitate the best combination of drainage and moisture retention, increase soil microbial populations, and encourage earthworm activity.

Its nutrient value for plants will depend on what ingredients went into making it – grass cuttings and weeds contain a lot of nutrients that will become available in the finished compost. Green waste compost from woodier materials will be a bit more acidic and fungally-dominated, and will especially suit perennial plants. Compost containing more green materials will be more bacterially dominated, which is good for annual plants.

Worm castings:

Castings is the name for worm poo, or compost produced when worms eat stuff and digest it.

Worms are an effective solution to composting fruit and veg waste, and a wormery can work well in a small space where many other composting systems are not an opetion.

Worm castings tend to be dense and moist. They cannot be used as a growing medium on their own, but can be very beneficially mixed with other soil or compost, or used as the basis for a compost tea feed for plants.

Castings are usually derived from fruit and veg waste, so they contain a lot of nutrients which are slowly released. They are an excellent addition to the soil for hungry plants, as a top dressing to be watered in, or as an ingredient in a potting mix.

Worm castings contain a lot of beneficial bacteria and enzymes, and help to support disease and pest resistance in plants.

Leaf mould:

Leaves from deciduous trees, if kept in a moist and aerated environment, will decompose by a fungal process into leaf mould. The process takes two years, although this timescale can be shortened by shredding the leaves.

Some people also accelerate the process by adding high-nitrogen amendments such as grass cuttings, coffee grounds, nettle tea or even urine, but strictly speaking this is not pure leaf mould as the extra nitrogen changes the biological processes involved.

Leaf mould has a wonderfully loose and crumbly texture. It is low in nutrients so it is an excellent medium for propagating seeds – especially those of woodland trees, for which it is their natural growing environment.

Leaf mould has a high fungal content and encourages development of mycorrhiza, which facilitates plants to regulate and optimise their intake and exchange of nutrients and water with soil organisms and other plants nearby.

Adding leaf mould to soil improves its structure and moisture retaining properties. Leaf mould is slightly acidic, and is beneficial to acid-loving plants and perennials.

Date: November 4, 2019

Leaf mould time again!

Here we are again, the time that the great yet oft-despised resource of autumn leaves fall at our feet.

As usual, since I started taking people’s unwanted leaf fall 3 years ago, I have been getting calls to pick up bags from local tidy-minded people. I do try to encourage people to make their own compost, but I still end up with tonnes of leaves each year, which is fine by me. I just hope that enough are left in situ for the wildlife that depend so much on them for shelter during the winter, and to rot down and feed the plants and animals in the soil where they grew.

One of many bags of leaves in my annual bounty!

Last week, I even got an email from a landscaper in Nottingham, England, whose company collects over 1,000 cubic metres of leaves every year, asking me if I would be interested in taking them away and how much I would charge! I was quick to decline, for many reasons, but wow what a wealth of leaf mould for the Merry Men of those woods!

My finished leaf mould sold well this year, with a lot of it going to Irish native tree growing projects. This was great, as it is a perfect growing medium for tree seedlings, and I got some financial return for the work of hauling the leaves, and turning and sieving the leaf mould during the composting process. Dunno how I’d get on with 1,000 cubic metres of the stuff though – I think I would need a bigger pitchfork…

Date: August 27, 2019

Why a new composting system?

In my 15 years working as a composting trainer, adviser, and researcher, I have met so many people who face the same issues with their composting. It’s a smelly heavy mess, they don’t know what is happening inside the pile, and it just isn’t easy enough to use.

The problem for most people, of course, is the type of compost bin they use – either a “Dalek” shape garden composting bin

Plastic compost bin
“Dalek” style compost bin – narrow on top, wider at the bottom, no airflow or permeability.
Image credit:

or the compost tumbler type that has become popular recently in Ireland and perhaps other countries also.

A typical compost tumbler – all the moisture that goes in, stays in. Contrary to what some people believe, this is not good at all.
Photo credit: Dave Beckers

These bins and tumblers do not permit quick or easy composting of the kitchen waste which is our main organic waste issue. They get full, wet, and heavy with smelly rotting food.

A much better solution is a wormery, but even these have their issues. They are often made of plastic and do not breathe or allow moisture to escape. The trays can become heavy and compacted (though not, of course, if operated very well). And if something goes wrong, the worms can be killed, although this is unusual.

A plastic wormery – much better than most other compost bins for dealing with kitchen waste, but the best has yet to come…
Photo credit: Dave Beckers

I decided to make it possible to have effective composting in a small space, by dividing the material into fresh, semi-fresh, maturing, and matured, while making space for airflow and drainage and preventing compaction.

2 box and 2 tray compost system
The box and tray system. Fresh material (a mix of “greens” such as vegetable peelings and “browns” such as sawdust) is placed in the tray, and when the tray is full then the next tray is used. When all trays are full, the material is emptied into the boxes underneath. One box is filled at a time, so that the contents of one box will have matured by the time the other box has been filled.

This system will allow easy management of all stages of the composting process. Every part should be light and easy to lift, and if something goes wrong it is easy to isolate and fix the problem (usually a matter of (1) chopping up food waste material into smaller pieces and (2) adding more brown material such as sawdust, leaf mould etc.).

And that’s it really! A minimum of 2 boxes and trays needed, perhaps 3 or more for a larger output of kitchen waste or pet poo.

Update: I have found for larger volumes of waste that an excellent option is to create a double height system by setting two boxes on top of another two.

double decker Magic Box
Stacked double deck Magic Box, with braces to hold the upper boxes in place. The boxes are not fixed together so can be disassembled easily.

Date: August 19, 2019

Building the perfect composting beast (Part 1)

Composting, whether hot or cold, consists of different stages of biological activity. In a large compost bin where new material is being added all the time, there can be a very mixed array of conditions within the bin. A large bin can also retain huge amounts of moisture from waste grass, fruit and vegetables, giving rise to smelly and swampy composting.

A satisfactory solution, as I see it, is to divide the materials into different stages of biological activity, which is to say different ages of composting.

Fresh material, when added to the composting system, is high in food for bacteria but also for flies, wasps etc. It rapidly changes form and turns to sludge, while still smelling like the material that it was (onion smells like onion, grass smells like grass and so on).

When a “green” composting material such as food or grass turns to sludge, the high moisture levels mean not enough oxygen for beneficial composting bacteria to survive. The sludge turns anaerobic, and starts to putrefy and smell rather odd…

The best way to avoid this is to ensure that all green materials are broken up into small pieces, and then mixed thoroughly with brown materials. As well, air space should be introduced wherever possible amongst the decomposing material.

The picture above is a prototype for a new design of composting system. It is loosely based on the milk crate composter system, which in turn derives from the terracotta pot system developed, as far as I know, in India. I won’t get into explaining those here, but do please look them up if you are interested.

The new composting system (working name “The Magic Box Composter”) can compost pet waste or fruit and veg waste from your kitchen. If you want to compost dog or cat faeces, that’s absolutely fine, but be aware of what you’re dealing with. These faeces contain pathogens which will not be killed off by a slow/cold composting process. Therefore, you should not use the resulting compost in areas where people or pets will be active, or for growing food plants in. But you should still be able to make fine compost, which will benefit the plants in your garden, as well as providing a solution your pet waste issue.

Date: August 19, 2019

Building the perfect composting beast (Part 2)

The working Magic Box (working title!) will consist, depending on volume of materials, of 2 or more of these boxes with inserted trays.

  • How it will work:
  • Site the 2 or more of these boxes ie by side, with a tray in each one and a lid on top.
  • Use the clips provided to prevent the lids from blowing away, if using outside.
  • The tray will be your receptacle for green and brown materials.
The tray (just to state the obvious)
  • Green materials are food waste, such as fruit and veg peelings and leftovers, plate scrapings, other waste food (beware of meat, fish, and dairy – they will compost but are more likely to cause smells and flies, so the management should be extra stringent).
  • Pet waste such as dog and cat poo is also a green material.
  • Brown materials are fibre rich such as shredded cardboard and paper, sawdust, leaf mould, shredded straw, hay etc.
  • Animal bedding or biodegradable cat litter will contribute to your brown materials also.


  • Spread a generous layer of brown material on the floor of the tray.
  • Chop any food waste into smaller pieces, if possible.
  • Some tougher items such as avocado skin and seeds simply will not compost for a very long time, and you can choose to leave these out if you wish.
  • Add the green material to the tray, spreading it out if there is a large amount of it.
  • Add more brown material on top.
  • Ensure at least 50% brown materials at all times – that means, if you put in a tub full of kitchen waste, you should make sure that there is at least a tub full of brown material added before and after the kitchen waste.
  • Sprinkle the mix with water using a watering can, and replace the lid.
  • Continue these steps until the tray is 3/4 full.
  • If you are going to fill a tray in less than a couple of weeks or so, you will need more than 2 boxes to make this system work properly.
  • When the tray is 3/4 full, you can place a sheet of damp newspaper on top of the material if you like, just to create a barrier against smells and flies, and leave the lid on it.
  • Then spread a layer of brown material on the floor of the next tray, and start filling that in the same way.
  • If you are using 2 boxes, continue until the second tray is 3/4 full.
  • Then lift out the first (older) tray and tip its contents into the box.
An empty box (alternative design with interlocking sides, not screws)
  • Set the empty tray aside, and tip the contents of the second tray on top of the first.
  • Then replace the 2 empty trays, and repeat the whole process of filling with browns and greens.
  • If you are using more than 2 boxes, the same method applies – simply fill all the trays to around 3/4 ways, then tip them all into the first box, in the order that you filled them.
  • If you have chopped up all food waste and mixed in enough brown material, there should be little or no sludgy texture or unpleasant smells.
  • If you think it is too wet, you can add less water in future.
  • If you think it is too dry, or is slow in starting to decompose, you can sprinkle more water to the material that you have placed in the box.

What you have done is to allow the initial stage of the composting process to take place in the trays. The green material should be beginning to break down nicely through bacterial action, while the brown material provides physical structure, fibre, and carbon to help the process. When the material is placed in the box it can enter a more mature stage of composting, and be ready for use when you need to remove it.

  •  Next, start the whole process again with your empty trays back in place.
  • When you remove the trays, you will find that the older material in the box has greatly reduced in volume from the composting process.
  • When the trays have filled this time, you can either add them to the first box again (if you think that there is room enough) or start to add them to the second box.
  • Do not fill a box too much – remember to leave enough room in the box that the tray can sit down into it and rest on the sides of the box.

Harvesting the compost:

  • When all your boxes have been filled, you can empty the box that you filled first, or you can fill up the trays again if you want to allow the compost more time to mature.
  • When you are ready to empty a box, simply lift the whole box off and set it aside.
  • Your compost should be ready for harvesting and using. Shovel it into a bucket or bags, and replace the empty box back into position.
  • Using this method, you should always have space for new material, assuming that you are using enough boxes and trays for your needs.

Date: June 12, 2019

Biodegradable and compostable packaging – rot or not?

I recently got a query from Plastic Free Kinsale, a wonderful community initiative that supports local people to reduce plastic consumption and increase recycling (check out their Facebook page).

The query was as follows:

Hi Donal, hope you are well. There was a great article in the telegraph newspaper about biodegradable plastic and composting recently. Tons of people messaged us about it – in the article it said that even compostable material in a brown bin isn’t ideal as mixing food waste and compostable material can be bad…I’m sure it’s not once heading to industrial composting but can you confirm or clear this up for me so that I can reply to her? Attached is a screen shot of her message to us on our PFK page

The article referenced is this one which sets out the issues and confusions, but unfortunately does not distinguish very well the terms involved. There is a vagueness and perceived interchangeability between the technical terms “biodegradable” and “compostable”, but they do not necessarily mean the same.

So hopefully this article will help to clarify the issue.

Wikipedia states that
“Many people confuse “biodegradable” with “compostable”. “Biodegradable” broadly means that an object can be biologically broken down, while “compostable” typically specifies that such a process will result in compost, or humus.

So “biodegradable” can mean many things, including but not limited to compostable. Non-compostable biodegradable materials can be made from plastic derived from crude oil, which has been treated to render it biodegradable.

“Compostable” materials are always made from plant-derived materials. Compostable materials when used commercially (as packaging, coffee cups, for catering purposes etc.) may be certified as compostable, and might carry a logo (e.g. the “seedling” logo which I will not reproduce here).

Okay, let’s simplify it. What does this mean for you, if you have these materials that you want to dispose of?

Compostable materials can be put in your brown bin, and your waste collector should not have a problem with this. They will compost under the high-temperature composting conditions that brown bin waste is subjected to. All brown bin waste is composted quickly, in a managed high-temperature environment, to kill off pathogens and render the finished compost safe for use.

However, you may find that compostable items such as coffee cups, disposable cutlery etc. will not decompose in your home composting system. This is because they are made to be durable for use, and the lower temperatures in your home compost pile simply will not break down the materials, at least for a very long time.

You can also of course use compostable bags and bin liners for your organic waste. The same applies – they’re fine in the brown bin, but slow to decompose in your home compost.


Biodegradable materials should not be put in the brown bin, as they may not be compostable. They should not be put with your recycling, as they may not be recyclable. So they should be added to your general waste for landfill, unless you want to try composting them at home – bear in mind that the news article linked above relates the story of a recent study by the University of Plymouth which found that biodegradable plastic bags were still capable of being used as bags three years after being buried underground because they had degraded so little.

Best option?

Avoid disposable containers where possible, whether they are compostable, biodegradable or whatever. Every disposable item takes unnecessary amounts of land, water, and energy to produce. It’s easy to keep a reusable coffee cup and washable cutlery in your car if you sometimes need to drink or eat on the go. We as consumers, and the relevant authorities, should also encourage vendors to facilitate customers bringing their own reusable containers and cutlery whenever possible.

Date: March 6, 2019

Leaf Mould – it never gets old!

Leaf mould is such wonderful stuff. Friable, crumbly, smelling of the forest floor.

It is great for adding to garden soil or raised beds, where it helps to loosen the soil and to retain moisture while also aiding drainage – how cool is that?

Leaf mould also works brilliantly as a seed or potting compost because of its texture and its low macronutrient content – composts high in macronutrients will most likely result in unhealthy growth in seedlings. I recently had the pleasure of supplying leaf mould for a “Forest in a Box” project This is a way for schools to propagate native trees in a 1×1 metre wooden box, protected from rodent predation with wire mesh above and underneath. Forest in A Box
Forest in a Box

The page linked above says that this space can produce 200 healthy trees for planting out every 2 years, so what a great use of a small space!

The beauty of leaf mould in this setting is that it provides the same fungi and microorganisms as the forest floor, so the tree seedlings feel right at home. The walls of the box encourage the trees to reach for the light, just like in the forest where competition for resources makes trees work harder and become stronger, though trees also help each other in surprising ways – plants are very altruistic creatures!

The mycorrhizal fungi that help plants such as trees to take up nutrients in a mutualist, symbiotic relationship between plant and fungus, also allow trees and other plants to pass on nutrients and even water to their neighbouring plants that need them.

And of course, these mycorrhizal fungi are present in the leaf mould. Leaf mould also contains valuable minerals – trees uptake minerals from deep in the subsoil using their roots, and when they shed their leaves they release some of these minerals. So whoever collects the leaves and makes leaf mould is also collecting the minerals that they contain!

Bagged leaf mould ready to go! – these leaves were dropped in 2016 so they are now fully composted, with no leaf structure left – see top image of leaf mould in hand.
leaf mould pile
A pile of sieved 2 year old leaf mould

Date: February 16, 2019

Wormery revisited

I reconfigured my big wormery in early December – cleared one end out and piled all of the finished compost plus uneaten food and bedding, and of course all of the worms, in the other end.

I did this mainly because there was some material that had become compacted, especially some shredded paper and cardboard that I had added as bedding. I figured that by turning and loosening all of the material, and leaving it a while, I should take care of that issue.

So today was my first time in about 2 months looking into the wormery. During the colder weather I didn’t want to feed them much anyway, reckoning that they had plenty to sustain them during their slowed-down winter activity. But wow! They have been busy.

Valentine’s Day must have come early for the worms (are they romantic or just eager?) because there are thousands, perhaps many thousands, of worm eggs in the compost now. These will all hatch in the next couple of weeks, and there will be many many new mouths to feed, so I’d better get cracking on collecting waste fruit and veg, chopping it up, mixing it with bedding and lime, and feeding the herd.