[APWG] Weeds may be due to soil nutrient levels, not invasive themselves

[Craig Dremann - Redwood City Seed Company]

Dear All,

Tests done last year on solid Italian thistle and medsuahead 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 commly used by farmers, plus some local
native seeds.

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 in 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 invasive, but when we test the soil, might just be
indicators that our cows and sheep ran away with too much of a key
nutrient, and we need to make a deposit in the soil nutrient bank instead
of fighting the weed.

Sincerely,  Craig Dremann (650) 325-7333