Wow, this is so crazy frustrating. Ever since I posted that video, I
am getting swamped by folks that refuse to believe what is right in
front of their eyes. And then they contact me to try to help me
understand why I am wrong.
I really don't think I can be more clear. All I can do is repeat myself.
Here, I will try to say it a different way:
A bioassay can indicate certain levels of persistent herbicides. So
if you do 100 bioassays with one type of compost, and then you do 100
bioassays with virgin topsoil with IDENTICAL FERTILITY, and you have a
50% death rate in the first set compared to the second set, then YES,
you most likely have a persistent herbicide problem.
If you have 0% death rate, then you need to grow it out to adulthood.
If the samples in the first set are the same size, then your compost
Here is the problem: nearly every bioassay I have ever seen done was flawed:
A) There was no control at all. If some peas germinate and grow,
this could indicate that there are persistent herbicides, but not
enough to kill the peas. Just enough to stunt their growth - but you
have no control to compare to, so you don't know if the growth is
B) The control also has persitent herbicides, or the control is
crappy dirt. The control must have soil that is equal in every way
with the exception that you KNOW for absolute fact that it contains no
persistent herbicides. Getting this control soil can be very
challenging. And I have yet to see ANYBODY doing a bioassay do this
THEREFORE: every bioassay I have ever seen first hand was useless.
Every single one.
Look at the raspberries in the video. Note how the raspberries on the
left are NOT DEAD! They are stunted. Granted, there are far too many
variables here to qualify as a proper bio assay - but that is not what
she was attempting to do. She ran out of contaminated material and
finshed the job with non-contaminated material. She probably applied
the exact same amount both sides. So this video shows typical
stunting of growth: a level of persistent herbicide that doesn't
KILL, but stunts.
Summary: nearly all commercial compost contains persistent herbicide.
If you can get peas to grow in it, then you have demonstrated that
the level of persistent herbicide is not high enough to kill your
plants, but I would say that there is a 98% chance that it is in there
and WILL stunt your plants. Plus there is a 98% chance that food you
eat from it WILL contain herbicides. Rather than bother with a
bioassay, I recommend that you not use commercial compost.
A bioassay that would be worthwhile: test 20 different commercial
composts and 20 different home made composts. I think those results
will be fascinating. In theory, a "professional" compost should
greatly outperform an "amateur" compost (I could fill a book talking
about this space). But I suspect that the #15 home compost will come
out way ahead of the #1 commercial compost.