The Basics

5 Essentials of Composting

Composting and the organisms involved, like all other life forms, need food, air and water to survive and thrive. The five essential conditions for successful composting are:

Green & Brown Materials

Composting organisms thrive on a balanced diet of green (nitrogen rich) and brown (carbon rich) materials. Green materials, such as grass cuttings, provide protein needed for growth and reproduction while browns, such as autumn leaves, supply energy.

Fortunately, most materials from the garden are well balanced enough to be composted all on their own, including old flowers, bush trimmings, old vegetable plants and weeds. The only materials that are too green and wet to be composted on their own are grass cuttings, food scraps and animal manure. On their own they will create a mucky smelly mess. If you want to compost these, they need to be well mixed with materials that are high in carbon such as leaves, straw, bush trimmings, sawdust, wood shavings or shredded paper. Although paper breaks down slowly, it can be used if other materials are not readily available.


All life needs moisture to survive including the different bugs and organisms in your compost. It is important to remember that the main composting organisms live in the film of moisture that surrounds each particle. Too little moisture and the composting organisms die off or go dormant. Too much moisture and they drown, creating a perfect environment for anaerobic bacteria that thrive without air creating nasty smells. Ideally, materials should be wet to the touch, as wet as a wrung out sponge but not soaking wet.

After getting the mix right, maintaining the proper moisture level is the key to successful composting, So:

• If your compost heap dries out, spray it with water when you are turning it.

• Keep your composter in a shady spot so it will not dry out.

• Always cover compost heaps with plastic, old carpet or some plywood. In most countries, this is to keep moisture in, but in Ireland, this is to keep the heap from getting too wet from all the rain in the winter months!

• It’s always best to mix and moisten materials before you add them so any excess moisture can drain off before going into the compost pile.

Size of Heap

While the size of the heap will be determined by the amount of material you have to compost and the system you chose to use, the ideal size is at least one cubic metre. A heap of this size can be made with materials accumulated over time (cool composting) or made all at once (hot composting).

When a large heap is made all at once with the optimal conditions for composting – the proper balance of nutrients, air and water – the breakdown of materials is so rapid, that the compost generates heat and can get as hot as 60-70°C. Heaps of one cubic metre in size or greater also have an ability to hold heat better because they self insulate.

Smaller heaps aren’t as good at holding heat and tend to dry out quickly, though bins with solid sides and a lid help keep smaller heaps warm and moist (like the compost bins provided by your local authority).

Just remember, larger compost heaps may require a little more work with turning to introduce air into the middle.


Just as with water, all composting organisms need oxygen. To promote good aeration and therefore good composting:

• Create lots of tiny air pockets by adding stems, stalks, wood chips and other rigid materials.With a good blend of materials and adequate moisture, the heat produced from composting creates a chimney effect, drawing air into the composting materials and promoting air flow up through them.

• Put a few inches of coarse materials at the bottom of your composter. This raises it slightly above the ground and helps air to flow underneath and up through the compost. This also improves drainage from the heap if it gets too wet.

• Don’t build the heap too big as larger piles can become compacted and this can squeeze the air pockets from the heap.While smaller heaps will get more air than larger ones, they do not heat up as much.

• Turning your compost regularly helps fluff up and aerate the materials. This helps restore the air spaces needed for the compost to “breathe”. Depending on your energy level and your need for compost, your compost can be turned weekly, monthly, annually or not at all.

Particle Size

When it comes to composting, the smaller the particle, the faster it will break down.This is because composting works from the surface of materials inwards. So to speed up composting:

• Chop woody materials up with a sharp spade or shears.

• As you garden, use your pruning shears to cut materials into pieces no longer than 10 cm.

• Run over leaves or weeds with a lawn mower.

• Put woody trimmings through a shredder.

Chopping materials up helps make a better mix when forming your compost heap. Keeping materials smaller also makes it easier to turn the heap later on for faster composting. Ideally, you want a mix of fine and coarse materials in your heap, for example small green grass clippings with chopped up brown hedge trimmings.

Remember that variety is the spice of the compost pile’s life! So mix it up and add as much variety as you can. Check out our Blending Materials Poster for more information on this topic.

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