i recently had a problem with rushing my "regular" compost from the tumbler, resulting in phototoxic compost which robbed my seedlings of nutrients. (they recovered quite nicely once i figured out the compost was the trouble.)
so i wondered if the vermicompost needs to rest or mature before being used? i mean the poo itself, and not the bundles of kitchen refuse in the bin.
agreed that worms have been poopin' in the ground for years, but it can be an issue of proportion, can't it?
for example, i have been throwing my immature "regular" compost on my garden, which has, at my *most* aggressive application, a ratio of 1:10 in the top 6 inches. but when i used immature compost in a 1:1 ratio with potting soil, i nearly killed my tomatoes seedlings, and stunted many others.
without a test, i will probably let my vermicompost age before using in such high ratios.
The proportions likely had a much greater impact on things than how "aged" any of it was.
If healthy soil is thought of as "food" for the plant, the worm castings can be considered a vitamin supplement. Vitamins are good. They can help give us some of what we're missing in our diet. Worm castings similarly for plant.
I know I'm sort of over-simplifying it, but if half of your diet consisted of food and the other half were vitamins, you might not do too well, either ;)
At most, I'd shoot for a proportion of 40-60% castings mixed with healthy (nutrient-rich) soil.
I have no idea how anyone can quantify vermicompost using any method or media. I have used the simplistic method of wooden bins originally and later plastic tubs when they came on the market. I use peat moss as my media of choice and water blend my kitchen or garden scraps before trench feeding to the worms. I remove a half inch or so of dried media from the tops of my bins twice weekly before feeding, and replace the removed media with soaked and drained peat moss. I can't say the removed surface media is all castings, so I just call it 'spent media'. I simply grate this media through a quarter inch screen and use it directly for a germination mix, or as part of my potting up mixes. I have never had a problem using vermicompost in this fashion other than there is never enough. I typically go though more than sixty gallons of this media each year.
For me this is an issue of efficiency. The worms eat the 'food' and leave the compost behind, but it is mixed in with food that they didn't eat. Also you don't want to throw away your precious worms...
So even when my worm bin seems jammed full of compost with very little food and bedding visible, when harvesting, I leave the 'harvest' in large sack for several months so that the remaining worms can eat what is left of the food.
Then I put a pint of so of bran porridge or ordinary oat porridge (made with water) plunged into the sack to attract the remaining worms, which I harvest and return to the main wormery.
Harvesting the worms for garden purposes doesn't seem to affect the population in my bins. Actually it keeps them in a growth phase which I think is healthy for the population. As for uneaten food in the vermicompost I use for my germination and potting mix, it is so insignificant I can't see any problems there. It's simply more compost material.