Here is an interesting email from Crissy:
Quick question about the use of vermicompost – does it go
bad, and if so, how do I know not to use it?
I harvested my worm bin for the first time back in October, which was
just before the rain started here. The compost was pretty wet, but
for the most part smelled like rich soil. I’d planned to let it dry
outside a bit, then store it in bags or jars and give it to my
gardening friends, but I misjudged the weather. It’s been sitting
outside in a big, fairly shallow plastic flower pot, loosely covered
with a tarp ever since.
I’ve decided that I want to give container gardening a shot this
year, and want to amend some old potting soil with the vermicompost.
I just want to make sure that it’s still okay to use before I get
Hi Crissy – that’s actually a great question!
I’ll start by saying “it depends”. What it depends on is how stabilized your vermicompost is. By definition, vermicompost is a ‘humus-like’ end product that results from the stabilization of organic wastes (thanks to the joint effort of worms and microbes). Humus is a highly stable material – very resistant to further breakdown. As an analogy, consider peat moss – or potting soil (which usually contains a lot of peat moss). If you soak brand new peat moss and let it sit indefinitely, it will never go ‘bad’ or decompose much further than it already has. This is the same idea with really good quality composts.
If there is still a fair amount of partially decomposed waste materials left in your vermicompost, there is a decent chance that these could rot further – and if this occurs under anaerobic conditions, you could end up with a material that is considered ‘bad’. In other words, it is basically the anaerobic breakdown of unstabilized organic wastes that results in nasty smells and the foul nature of ‘rotten’ materials. Believe it or not, if you ground up fresh chicken meat (an example of a material that would be really nasty if rotten) and mixed it with a LOT of peat moss or some other bedding material (along with some mature compost for good measure) and provided the mixture with a LOT of oxygen, it would compost just like anything else.
Farm animal mortality composting is actually quite common. It is next to impossible to eliminate ALL anaerobic microsites in a mixture, so there could still be some odors – but its amazing what you can do when you add enough bedding and provide enough oxygen.
Anyway – I’m getting sidetracked here.
Good vermicompost should keep for quite some time (sometimes years) – and it really only loses its potency, rather than going ‘bad’. If it is sitting outside, exposed to the elements, the quality can degrade quite quickly – but if covered up, it should be totally fine for at least multiple months.
It certainly won’t hurt to use it, either way (again assuming it is good quality stuff to begin with). Just mix it up and take a whiff. If it smells rotten, mix it some more then put it somewhere dry to sit (on top of multiple layers of corrugated cardboard might help to draw out excess moisture). It should eventually become aerobic (with the rich, earthy smell of good humus), and useful as a soil amendment.
Hope this helps!