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  • From: Ted Patterson <patters AT erols.com>
  • To: "Market Farming" <market-farming AT franklin.oit.unc.edu>
  • Subject: Re: Problems starting plants & herbicide persistence
  • Date: Wed, 21 Mar 2001 09:38:33 -0400


At 12:23 PM -0500 3/15/01, Alliums wrote:
>It's the potting soil -- it's too dense and the seedlings can't form roots.

Okay, Alliums..... I hesitate to offer advice to a woman who carries home
blue ribbons from the Pennsylvania Horticultural Society harvest show, and
especially to a friend and neighbor, but here are a couple of points to add
to the discussion on potting mixes and herbicide persistence.

We've already talked about wetting agents in nearly all the consumer bagged
potting mixes. And it's no small point for the organic growers I know who
go to great lengths and often expense to get acceptable mixes. I'd just
add that it's a positive reason for being hooked up with an organic
certifying agency, where they can help direct a grower to suppliers and
where you can join in quantity deals with other growers.
But, Dorene, with the resources you have and with all due respect to the
Scotts empire, you can definitely lay off the ProMix and roll your own
potting mix--because you've admitted having the magic ingredient, worm
compost. You already have leaf compost, vermicompost, rock powder, a
little topsoil, and all you need to buy is vermiculite or perlite for the
all-important aeration. You said:
>I germinate in a plug tray of 100% ProMix, then
>put in newspaper pots with 50% ProMix and 50% worm castings.

You don't need to go so heavy on your precious worm castings. Kelly
Slocum, the Washington state worm guru, has often said that if you're using
vermicompost then it should comprise no more than 1/3 and typically about a
1/4 of the total growing medium. She points to research by Washington
State University and Dr. Scott Subler which I think was written up in Worm
Digest. This was their recipe for a general purpose potting soil:
5-17% worm castings
30% clean top soil
10% perlite or vermiculite
25% organic matter
18% coir fibre (replaces peat moss)

And here's an old quote from Kelly: [[Now, if you're actually using
vermicompost and not pure castings then you'll use 25% vermicompost in
place of the castings and reduce the amount of organic matter
correspondingly.....
There is no single definitive recipe for potting soil as different plants
will have different ideals. What Scott's research shows, however, is that,
if you're using pure castings as a portion of your growing medium then it
should comprise between 5 and 17% of the total, regardless of the plant
being grown. With castings as more than 17% of the total plant growth and
vitality showed decline (though flowering and fruiting increased, if only
slightly). What to use for the remaining 83-95% of the mix can be whatever
you like.]]

Finally, on herbicide persistence in compost, you said:
>If you hot-compost, then most of the pesticides/herbicides will break down.
>If you let it cold compost for a looooooooooong period of time, most of the
>stuff is supposed to go down, too.

That's a general statement, and I like to believe it because I've carried
away a lot of township compost in my pickup, but unfortunately we're
probably being too optimistic and maybe whistling past some persistent
chemicals.

At this winter's PASA conference, in a talk on Penn State's high tunnel
research, there was a sidebar discussion on a problem they had in the
compost they got from their own campus composting facility. They describe
the compost as MSW but my understanding is that it is composted leaf and
lawn clippings from the campus, and they found tangible levels of
clopyralid. You can get a summary from Eric Burkhart at Penn State
[epb6 AT psu.edu], and I hope he won't mind if I quote his concluding
paragraph:
[[In a recent paper by Rynk (2000), it was reported that similar symptoms
and problems have been documented in Washington State, where a University
MSW composting operation had been receiving complaints associated with the
use of their product. At this facility, subsequent testing (by the same
laboratory as was used for the Penn State samples) found that clopyralid
residues as low as 0.03 ppm were likely responsible for an epidemic of
widespread phyto-toxicity. Similarly, research at Michigan State
University in the mid 1990s found that this particular compound is quite
persistent throughout the composting process. For example, in an
experiment conducted using grass clippings as the primary composting
medium, it was found that clopyralid levels decreased from a high of 32,000
ppb to a low of 100 ppb over a period of 365 days (Vandervoort et. al.,
1997). This corresponds to 32 and 0.1 ppm, respectively. Considering that
levels as low as 0.03 ppm may be phyto-toxic, this research suggests that
significant residual levels may persist after even a year of composting.
These findings corroborate the hypothesis that the bell pepper and cut
flower deformities noted here at Penn State are likely the result of
residual clopyralid activity associated with the use of MSW compost.]]

The two papers he cites are--
Rynk, R. 2000. Dealing with herbicide residues in compost. BioCycle.
Sept.: 42-47
Vandervoort, C., M.J. Zabik, B. Branham, and D.W. Lickfeldt. 1997. Fate
of selected pesticides applied to turfgrass: effect of composting on
residues. Bull. Environ. Contam. Toxicol. 58: 38-45

I apologize for the length here. But this herbicide persistence is a drag.
Many of the veg growers and CSA's in our area face encroaching housing
development, and one unusual benefit they can derive is being able to take
in carbon--leaves and grass clippings--from landscapers and nearby
municipalities. All the more reason for us to encourage suburban
homeowners to get their lawns off drugs.
-Ted Patterson Wayne, PA





  • Re: Problems starting plants & herbicide persistence, Ted Patterson, 03/21/2001

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