For years I have been reading and watching YouTube videos about the Johnson-Su composting bioreactor.
Last week it was cold, windy and drizzling so I needed an indoor project for Steve, our two-day-a-week handy man and hedge sculptor, and myself. Perfect - let’s build a bioreactor!
The compost it produces provides nutrients, and of more interest to me, gives the soil a microbial diverse and fungal-dominant microbiome. As Dr Johnson says, his compost introduces beneficial microbes to the soil “like a baker introduces yeast to bread dough, the increased presence of fungi appears to be a key indicator for soil quality, both in the terra preta soils of the Amazon and the compost produced in the Johnson-Su bioreactor”. There are many scientific papers out there showing the incredible increases in plant health and growth rates after this compost is added to your soil.
So off we went. Thankfully, the building materials are readily available; a hardwood pallet, wire re-mesh 10 gauge, 5 x 300cm 10ft lengths of 10cm 4inch wide pvc pipes with drilled air holes, weed mat and a rebar jig to hold the pvc pipes in place during filling. Detailed instructions are all over the web just google 'Johnson-Su composting bioreactor'.
When it was assembled, we put it on a flat site adjacent to the current composting area. We were then ready for filling. The material that you choose to use can vary, but as the aim of the game is fungal-dominant compost, I recommend leaning towards carbon sources such as brown leaves, wood chip and straw.
We have a ton of leaves at this time of year, so we ran them through our chipper mixed in with some wood chips and horse manure. After each third of filling we added a layer of grass to push the thermophillic temperature up quickly, to 165F /75C, in those first few days.
All material that goes into the reactor must be pre-wetted thoroughly. It’s is also best to add it in for one day to get compaction and setting before the pvc pipes are pulled out after 24 to 48 hours. All up it holds 800kg or 1800 pounds of wetted materials - that’s 75 large buckets!
Allow 4 or 5 hours to wet, drain and fill. Once full, we placed a dripper on top that turns on for 2min each day. This is important as the material must stay moist at all times. When the pvc pipes are pulled out, 5 air tunnels remain in place and hold their form. Given that no material is more than 30cm or 12inches from an air source, there is no need to turn the compost.
It will take 8 to 12 months until the final product, a fungal-dominant clay-like soil, is ready for use in the garden as either a direct additive or a base for a slurry that can be sprayed or spread on larger orchids, paddocks and gardens.