Dark Arts: How to create hot compost
With a bit of planning and effort, in just18 days you will have a rich, crumbly, sweet-smelling pile full of beneficial biota and organic matter to add to your soil.
HERE’S the real dirt on hot composts: they take relatively little time to make, you reap almost 100% of the volume of material you put in and it’s glorious for your soil. They take a bit of planning to gather the material and they need to be turned every two days, but in just 18 days you will have a cubic metre of rich, fragrant, crumbly compost to add to your garden.
The Berkely Method of creating hot compost works. It’s been tested hundreds of times around Australia by us and by others and it’s easy to construct. The beauty of this method is its simplicity: anything that was once alive can go into the compost heap.
Your ingredients fall into three equal piles of:
Brown (dried grass/garden clippings/chipped wood etc)
Green (organic kitchen scraps/lawn clippings/fresh garden clippings etc)
Black (manure such as cow, horse, sheep or a mix of these)
The hot compost doesn’t really work under 1m3 and you will need twice this area so that it can be turned. We found using open three-sided corrals helpful because the pile can be mounded high whereas it’s hard to get the pile high out in the open, but it all works. Regular turning exposes all surfaces to the air allowing breakdown by a range of aerobic bacteria. The pile needs to be kept moist (squeezing a handful should yield a drop of water). Try to get all the plant and wood material chopped up small (2.5cm pieces). Adding woody material is particularly beneficial because it is broken down by fungi – you will see white cobwebby strands of hyphae in the compost pile. In the soil these will create extensive underground networks and form associations with plant roots exchanging nutrients for carbohydrates so that plants remain healthy and resilient.
Activators such as Nettle or Yarrow are great for putting in the middle of your pile to kick start the process but If you leave them out the process will still work just fine. Permaculturalist Geoff Lawton, from Zaytuna Farm in NSW, Australia, was in the US giving workshops and added a whole deer that had been left as roadkill to a compost pile as an activator. After 18 days there was no identifiable material left: Nature at her best.
Pros and Cons
Now let’s compare Hot Compost to traditional Cold Compost. The Cold Composting method can take anything from six months to a year, depending on the weather, to yield only a small amount of admittedly nice compost – the final result of breakdown of organic material by anaerobic bacteria, particularly if the pile is not turned regularly. The good thing about Cold Compost is that it is usually tucked away discretely in the garden – often in a large plastic bin or piled up in corrals and even fenced with chicken wire – and can be fed regular amounts of kitchen scraps as they are generated.
The Berkely Method of Hot Composting, on the the other hand, uses a lot of material and space in the garden and takes effort, but in return it yields a lot of compost in a relatively small amount of time – 18 days.
We like to do a Hot Compost per garden each year, have some Cold Compost bins on the go with a worm farm and a Bokashi bin as well. They all work in different ways and all help to turn waste into garden gold.
Some Benefits of Using Hot Compost
Increases soil permeability and structure, helping plants to grow extensive roots and reduce the amount of watering needed.
Supplies a huge diversity of plant nutrients.
Encourages a range of microorganisms to flourish that supports healthy soil life and plant growth.
Helps control plant diseases and pests.
The 18-day Berkely Hot Compost MethoD
Ingredients
1/3 part “Brown” (Carbon): hay, shredded wood, sawdust, dry leaves, straw, shredded paper.
1/3 part “Manure”: or other high-nitrogen material such as fruit and veg scraps.
1/3 part “Green”: fresh green garden waste, veggie scraps and lawn clippings.
(Optional to jump start the process) Activators: comfrey, nettle, yarrow, worm casting tea, urine, animal/fish carasses.
Method
The compost pile needs to be at least 1m3 in order to get the temperature high enough.
Shred or cut Brown material in small pieces (about 2.5cm). Wet Greens need not be shredded.
Start with a layer of Brown on the bottom and build the pile like a lasagna. End with a layer of Brown.
Optional: Add a layer of Activator in the middle or sprinkle it in small amounts throughout the layers.
Water each layer as you build and when you finish until the water runs out the bottom of the pile and a squeezed handful yields one drop (one drop is good; two drops is too much).
Loosely cover the pile with a tarp to maintain moisture and heat (generated by the bacteria, even in the coolest of temperatures).
Turning the Pile
Turn the pile with a garden fork on Day 4, then every 2 days after that to Day 18.
The top layer of the old pile should become the bottom layer of the new pile; turn so that the outside layers become inside layers and vice versa. This allows a mix up of microorganisms, carbon and oxygen.
Check the temperature in the centre of the pile before you turn and add water after turning. You’ll see the pile quickly starts heating up. The second and third turns are the hottest (min 50C; max 70C) after which the temperatures will come back down. If you don’t have an old roast thermometer you can dedicate to composting, you can put your (gloved) hand into the pile to check the temperature. As a rough guide, 40C is like a hot day and 70C is too hot to bear for more than a second or two.
Troubleshooting
If the pile goes above 70C or smells bad, it’s likely you have too much nitrogen and it’s getting too hot. Turn the pile on to a bed of sticks for aeration, add sawdust (Brown) to take the temperature down, make a hole (like a chimney) down the middle of the whole pile to release the heat and remove the tarp while continuing to monitor.
If the pile is not heating up or starts to cool down too fast, it’s likely you have too much carbon. Add blood & bone to the layers to jump start the composting process.
Check the water at each turn using the squeeze test. Add water if it’s dry or create a chimney in the middle if it’s too wet.
Getting the hang of it
You’ll know your compost is working when by Day 10 your pile is warm, brown, smells good and starts developing a nice texture. By Day 18, the temperature should drop, it should be sweet smelling with a fine, rich chocolate texture with no identifiable material. We’ve had only an occasional pile that needed one or two more turns after Day 18, which we judged as slightly undercooked using the texture and temperature as guides. Earthworms love these hot compost piles but won’t move in until the temperature cools down and can often indicate when a pile is done. Just one aside: turning the compost pile usually takes about 20 minutes and is easier the lighter and more composted the pile gets. We think of it as a workout.
The more you do, the more you’ll get the hang of it. You’ll get to know what a great finished pile should look like, what the temperature curve looks like over the 18 days and how moist to make your pile. Use whatever materials you have to hand such as autumn leaves from street trees, free shredded wood mulch from your local council depot and veggie scraps from your local organic grocer (they’ll be happy for you to take them away). One of the best piles we ever made included large amounts of lawn clippings donated by a suburban lawn contractor (believe it or not, a rare commodity in the inner-city). We discovered police horse stables in the city, dressage stables for teenage girls in the suburbs and even stables catering for tourist carriages rides around the CBD that were all only too happy for us to cart their manure away.
Try making a hot compost pile with a friend and split the results – offer to do one in your local community garden and create a roster where everyone can help turn the pile in pairs with someone more experienced pairing up with someone new to the process. Run hands-on workshops like we did with a materials collection run the day before, a rundown on the day of some of the many benefits with everyone joining in to build the compost followed, naturally, by a celebratory sit down lunch after all the hard labour!
