Can spent potting mix be used in compost?

[clydefrancis]

when repotting can the spent potting mix be recycled into a cold composting bin as a layer between each layer of organic material?

[MitchellMc]

Welcome to the Bunnings Workshop community @clydefrancis. It's fabulous to have you join us and many thanks for your question.

Since you are specifying that the potting mix is "spent" I don't see any reason why it couldn't be substituted as a brown layer in a green/brown composting sandwich. I guess my only question would be if it is completely spent is it actually adding anything beneficial to the compost? It might not need to if it is balancing out a green layer.

Let me mention the very knowledgable @Noelle and @Adam_W to see if they can shed some light on the mystical science behind cold composting. I'll certainly be looking forward to hearing the answer.

Mitchell

[bergs]

Hi @clydefrancis 

If and when I'm repotting plants the old material goes into my compost bins. With all the other nutrients like grass clippings, kitchen scraps etc. it helps to bulk the mix up. I use it to cover the veggie scraps or the clippings. When I replace any soil from the beds it goes into the compost as eventually it will be rejuvenated and is able to be reused full of goodness again. If you compost correctly you put a layer of wet followed by the same layer of dry and then manure and stir it up every couple of weeks. I even shred up all my paper and put in as the dry layer as well. Seems to work for me as the worms do the job. 

🍻Cheers 

[clydefrancis]

Hi Bergs,

Thank you for your input to my post. It helps. My composting practice is a layer of organic material, dusting of lime followed by a dusting of blood and bone . I had not considered a dry layer but it sounds like the  way to go. Dusting is a couple of hands full.

[Adam_W]

Hi @clydefrancis no worries at all putting old potting mix into compost, as @bergs said it's great for bulking the mix out & as a 'dry' component.
The [very] rough rule of thumb is 50/50 wet and dry or brown and green in a compost system. So think dry leaves as your dry/brown and grass clippings as your wet/green.
You'll find all sorts of other 'recipes' but this is a good starting point.
Blood & bone or seaweed weed solution or GoGo Juice or similar are good to add to a heap as they are biological activators. It's bacteria etc. that power the composting process so adding those products keeps the population topped-up.
I'm not quite sure why you are regularly adding lime. Normally lime is only added when a heap gets too wet and starts to go 'sour' (acidic) and the lime reverses that.
It can help with calcium levels but a better way to add organic calcium is through crushing up eggshells and adding them.