If there is one thing our Horticulture students want to know when they start a course with us it’s “will we be making compost?”. The answer to that is of course, YES!
Good compost is the cornerstone of a productive and healthy garden and it’s easy to produce your own on a small or large scale.
Lets start with some basic rules of composting.
What to put into compost?
Things that are good for your compost include basically anything that was once alive. But balance is the key! A compost bin full of weeds or packed with grass clippings wont give you everything you need. So, it’s about the balance between Carbon and Nitrogen. This balance can also be described as “Brown to Green” ratio.
A good ratio of brown to green is 2 or 3 parts brown to 1 part green.
Greens are things like grass clippings, vegetable waste, fruit peel (not citrus), annual weeds before they have set seed.
Browns are things like straw, wood chips, leaves, shredded brown cardboard, bedding from herbivorous pets like guinea pigs and rabbits.
What else does a compost heap need?
Every compost system needs air. A good airflow is needed to circulate through the pile to keep oxygen available to the microbes and microorganisms doing all the hard work breaking down the raw materials. This stops the compost becoming “anaerobic” and smelling acrid.
The other thing your compost pile needs is water. Remember, essentially the compost heap is a huge colony of living organisms. They need water to be able to do their job transforming the raw materials into nutrients that can be used by your plants. A good rule for water in compost heaps is “moist but not wet.”
What size should a compost pile be?
The short answer to this is “as big as you find manageable”. That said, staying above a 1 cubic meter is a good starting point.
Compost bins vs bays, vs piles.
There are lots of different composting systems available to buy or build. The system you choose will largely be determined by how much room you have available and how able you are to maintain the system.
Plastic compost bins are available from almost all hardware stores. They are typically round and have an open bottom and a tight fitting lid. They are great for those that don’t have a lot of room but there are a few things to look out for.
Firstly, be aware of the limited capacity of the bin. Always maintain the “brown to green” ratio. Don’t pile in lots of grass clippings at once. They will restrict airflow and form a dense slimy mat which will stop bacteria and microorganisms from doing their work. Also, make sure you put some aviary wire across the bottom to stop vermin getting in.
Compost in plastic bins will need turning over about once a month.
For those with a bit more room, try constructing a series of 3 bays that are 1 cubic meter each. The walls can be made of anything, sleepers, pallets, roofing iron etc.
The idea is that you fill the first bay with raw materials, following the green to brown ratio. As this starts to break down, bacteria will get the process moving and create a cool temperature system. After about 6 to 8 weeks, transfer the contents into the second bay and re-fill the first.
The compost in the second bay will continue to break down and get warmer as it does. Repeat the process by moving bay 2 into 3 after another 6-8 weeks. Keep an eye on the temperature by sticking your hand into the second bay. It should be nice and warm but not hot. The third bay will be the hot bay. The bacteria here will really work hard breaking down the last of the mix. This bay will reach about 60 degrees C. After a month or so, it will be ready to use.
You will know your compost is ready when it’s light and fluffy with a soil like texture. It should smell almost sweet, not acrid or sour.
Save a bit from the third bay and put it back into the first and second bays. This helps maintain bacteria numbers in the first two bays and gives those bays a kick start.
A system used in the no-dig areas at the Royal Tasmanian Botanical Gardens is to make a layered pile. The advantage of this system is that it does not require turning.
Firstly wet a couple of bales of hay. Spreading them out and soaking them in a wheel barrow is a good way to do this. Lay down a 150mm layer of wet hay in a fluffy 1 meter square. Put in two star pickets to support the following layers. Add chicken manure at 150g per m2 to the layer of wet hay. Add 150g per m2 of rock dust or zeolites. Next add 150mm of chopped greens spread right to the edge. Repeat hose layers until the stack reaches 1m high.
Leave the stack for a few months and then dig in from the top down.
Some “do’s and don’t’s ” of composting.
Follow the Green to Brown ratio.
Add water to keep the compost hydrated but not wet.
Monitor the temperature to make sure it’s working.
Keep vermin out by excluding them with wire.
Add a catalyst (available at your hardware store) if there is no existing compost in the system or the system is not in contact with the ground.
Add dog or cat manures.
Use weeds that have already gone to seed.
Use citrus peels, detergents or fats and oils.
Over load the system.
Compact the layers.
Having a good supply of healthy compost to use in your garden is a very valuable resource. It will help in every aspect of your gardening and add beneficial microorganisms, invertebrates and bacteria to your soils. It will also aid in water retention.
If you want to know more, have a look at our Horticulture short courses, community courses and certificate courses . Good luck!