[RWG] Some weeds may just be there, because of low potassium

[Holly Sletteland]

I read a book quite some time ago called "Weeds - Controlling without
Poisons" because I was all organic at the time (and still am in my gardens)
and was searching for alternatives to chemical herbicides. That was
basically the whole premise of the book.  I think there is certainly some
truth to it, as obviously weeds, like any other plant have soil conditions
that they are best adapted to, but my experiments didn't yield particularly
satisfying results. It also seems that at least Italian thistle does very
well invading oak woodland understory that is relatively intact. But I would
be interested in seeing more information on your methodology. 

-----Original Message-----
From: rwg-bounces at lists.plantconservation.org
[mailto:rwg-bounces at lists.plantconservation.org] On Behalf Of Craig Dremann
- Redwood City Seed Company
Sent: Thursday, November 10, 2011 5:13 PM
To: rwg at lists.plantconservation.org
Subject: [RWG] Some weeds may just be there, because of low potassium

Dear All,

Tests done in California this year on solid Italian thistle and Medusahead
grass infested area, point to their infestations are largely due to lack
of potassium in the soil.

When California's understory was converted from a perennial bunchgrass
community to annual exotic weeds 100+ years ago, these exotic plants are
very efficient soil nutrient scavengers.

A lot of work has been done to manage two weeds in our State, the
Medusahead grass and Italian thistle, without much luck, because the
causes of the infestations were unknown until now.

Using a $5 soil test kit that you can buy for your garden at most hardware
store, you can test the top inch of soil in a Italian thistle or a
medsuahead grass area, and see that it the potassium has been removed by
decades of grazing, and might be bouncing right around zero.

In the experiments I did this last year, I used cheap and easily available
bulk Potassium sulfate that is commonly used by farmers, plus some local
native seeds.  This may be an easy solution for annual and biennial weeds
that seem to resist other methods, like cheatgrass, yellow star thistle,
etc.

By adding local native seeds at the correct pounds per acre, and adding
the right amount of potassium, you can get a nice stand of natives in the
place of either of these two weeds within six month.

So instead of these two plants being considered bad weeds, we should now
look at them as soil potassium indicators, and that they are trying to
tell us that our potassium soil level is on empty, in the areas that they
colonize.

I hope that this information is useful to others working on weeds that
look like they are invasives--but when we test the soil, these plants
might just be indicators that our cows and sheep ran away with too much of
a key nutrient--and we now need to make a deposit in the soil nutrient
bank, instead of fighting the weed.

Sincerely,  Craig Dremann (650) 325-7333




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