Adding bones or shells to our compost pile is fine – if we have good rodent control in place – but we will notice that these ingredients will still be present when the compost is finished, pretty much intact, just stripped of any meat and residue.
Bones and shells are actually high in nitrogen, with collagen making up much of their structure, but these proteins are encased in protective calcium and phosphorus layers that make it very hard for compost bacteria to break them down or plant roots to access the nutrients.
Calcium and phosphorus are both nutrients that we want in our garden and are often lacking from our poorer central Victorian soils, but even in hot compost piles the chemical bonds of the bones and shells won’t break down. So, what should we do with these useful, but nutritionally unavailable materials?
We can fast-track the break-down of these structures by burning bones and shells in a small fire, using heat to chemically break the bonds and release those nutrients.
Any bones or shells I fish out of a finished compost are stock-piled in a dedicated bin. Then, a couple of times a year I will build a little fire, stacking up alternating layers of wood and bones and shells, till I have a nice little ‘camp fire’.
I keep a little stack of extra twigs and branches to add to the fire to make sure the pile burns nice and hot, with minimal smoke and right through. I use long-handled barbeque tongs to move any bones or shells that fall out, back to the hot centre of the fire. The bones can smell a little ‘proteiny’ when they burn, but it is not an awful smell.
Always check and adhere to fire regulations, even with a small fire.
Once cooled, the residual bones and shells can be collected up, and the wood ash sieved out. If the burn has been successful, they will have changed colour to chalky white and be very brittle, and can then easily be pounded into a bone-meal powder. A big mortar and pestle is ideal, but a sledge hammer or mallet on a concrete block does the job pretty well.
Our bone-meal powder can then be added straight to the garden, but I prefer to dust it into the layer of my compost piles, adding this nutrient back to the garden with the next dressing of compost.
Bone meal is also the secret ingredient in bone china and some pottery glazes.
Alex Perry of Bar Midland in Castlemaine is a keen hot composter who uses the YIMBY continuous hot compost system to process the food scraps that come out of his kitchen garden and from the restaurant, including lots of bones from stock and gelatine production. Bones coming out of Alex’s compost pile are being heated and powdered to go into the bone glazes that Bar Midland co-owner Lowden Cooper is turning into beautiful bowls, plates and serving vessels for the restaurant.
Another great use for these valuable resources.
– Joel Meadows works with *Yes In My Back Yard, (YIMBY), a community-scale composting initiative in Castlemaine and surrounds. Send questions or comments to hello@yimbycompost.com, or to book in for a compost workshop.
