“I would like to know your thoughts on tree stump grind as a source of worm bedding. I know it does not have much nutrients. My neighbor has a tree trimming business and offered it to me. Should I check it for toxins? Thanks” ~ Susan
The long story short – wood chips, sawdust, and any related materials (such as stump grind) are not ideal for use as worm bedding.
They are highly resistant to decomposition, but probably even more importantly, they do not hold water very well at all.
This is a really important consideration for any bedding material, since you not only want to avoid having moisture pool in the bottom of your system (or pass right through in the case of a bin/bed with drainage), but you also want to be able to retain enough moisture in the composting mass to keep the worms well hydrated.
Other wood-based products like cardboard/paper/newsprint are all much better choices. They all have really high carbon-to-nitrogen ratios and can take some time to break down (although nothing like actual woody wastes), but they are very absorbent, thus providing the worms with a nice habitat.
Another thing to consider – as you pointed out – is potential toxins in the wood. Conifer woods in particular can contain oils that can irritate or harm worms. Cedar is a prime example – and in fact, I’d recommend that you don’t even build a worm bed using this wood, since the harmful compounds can leach out into the bedding, resulting in worm mortalities.
All that being said…
I should point out that all hope is not lost.
If you have access to a lot of ground wood waste, I would recommend leaving it to sit and rot outdoors for a few months. If you also have access to manure, you could probably even enhance the process by mixing them together. Once these ground up woody wastes start to rot, they will be much more absorbent and will also provide more food value for the worms.